CA2360441A1 - Semiconductor laser device - Google Patents
Semiconductor laser device Download PDFInfo
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- CA2360441A1 CA2360441A1 CA002360441A CA2360441A CA2360441A1 CA 2360441 A1 CA2360441 A1 CA 2360441A1 CA 002360441 A CA002360441 A CA 002360441A CA 2360441 A CA2360441 A CA 2360441A CA 2360441 A1 CA2360441 A1 CA 2360441A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
- H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/0206—Substrates, e.g. growth, shape, material, removal or bonding
- H01S5/0211—Substrates made of ternary or quaternary compounds
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/0206—Substrates, e.g. growth, shape, material, removal or bonding
- H01S5/0211—Substrates made of ternary or quaternary compounds
- H01S5/0212—Substrates made of ternary or quaternary compounds with a graded composition
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
- H01S5/042—Electrical excitation ; Circuits therefor
- H01S5/0421—Electrical excitation ; Circuits therefor characterised by the semiconducting contacting layers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
- H01S5/042—Electrical excitation ; Circuits therefor
- H01S5/0425—Electrodes, e.g. characterised by the structure
- H01S5/04252—Electrodes, e.g. characterised by the structure characterised by the material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
- H01S5/2004—Confining in the direction perpendicular to the layer structure
- H01S5/2018—Optical confinement, e.g. absorbing-, reflecting- or waveguide-layers
- H01S5/2022—Absorbing region or layer parallel to the active layer, e.g. to influence transverse modes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
- H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
- H01S5/2205—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers
- H01S5/2214—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers based on oxides or nitrides
- H01S5/2216—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers based on oxides or nitrides nitrides
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
- H01S5/343—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
- H01S5/34313—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser with a well layer having only As as V-compound, e.g. AlGaAs, InGaAs
Abstract
A semiconductor laser element (30) comprises an n-type GaAs substrate (32) having a band gap energy of Eg1, on which are epitaxially grown an n-type AlGaAs cladding layer (34), an active layer (36) formed as a 2-layer quantum-well structure of InGaAs and GaAs and having a band gap energy of Eg2 smaller than Eg1, a p-type AlGaAs cladding layer (38), and a p-type GaAs cap layer (40). The cap layer and the p-type cladding layer have stripe mesa structures.
Passivation film (42) of SiN is formed in the areas except on the cap layer, and a p-side electrode (44) is formed on exposed part of the cap layer and the passivation film. An n-side electrode (46) consisting of a metal laminate of In/AuGe/Ni/Au is formed on the back of the substrate, and an InGaAs layer (48) lies as an absorber medium between the GaAs substrate and the n-type electrode.
Passivation film (42) of SiN is formed in the areas except on the cap layer, and a p-side electrode (44) is formed on exposed part of the cap layer and the passivation film. An n-side electrode (46) consisting of a metal laminate of In/AuGe/Ni/Au is formed on the back of the substrate, and an InGaAs layer (48) lies as an absorber medium between the GaAs substrate and the n-type electrode.
Description
0~1- 7-12;16:21 ;[,,FAX03-6286-0863 ;0362860863 # 3/ 32 SEMICONDUCTOR LASER DEVICE
FIELD OF THE INVENTION' s Tile present i~ivel~t.ion relates to a semiconductor laser device, and more particularly to a semiconductor Iaser device which has a linear ch2racteristic between injected current and oplic;al output and achieves a stable oscillating spectrum, and which is particularly suitable for applications in optical communications.
io BACKGROUND UF' THE 1NV~.N'1'.IUN
Semiec~nductor laser devic;GS are commonly used for applications in. optical communications. In particular, InGaAs 980nm-band semiconductor laser devices axe frequently used as the s pumping light source for optical amplifiexs in optical fiber communication systems.
The setuicouductor laser device for use as the pumping light source for the optical amplifier, for example, is required to have a stable optical outPnt and emission spec.~trum with rCSpec:l to the Z o inj ccted current.
Specifically, the current versus light output characteristic is IC(~uICCCl to be linear iu older to iiicr case the reliability of the optical amplification operation, for example. It is also preferable that the emission spectrum is in the stable longitudinal multimode lacing 'for as suppressing the influence of returned li,~ht.
,01- 7-12;16:21 ;~ FAX03-5296-0963 ;0362960863 # 4/ 32 Referring to Fig. 4, the structure of a conventional InGaAs 980nm-band semiconductor laser device will be described. Fig. 4 is a sectional vices sliowi~xg tlxc structure of the conventional InGaAs ~SOnm-band senuiconductor laser device.
s As shown in Fig. 4, the conventional TnCTa,A.s 9ROnm-hand semiconductor laser device 10 has a layered structure including an n-type GaAs substrate 12 having a thickness of 100E.irn. On the substrate, an n-type AIGaAs cladding layer 14 having a 2Nan film thickness, an active layer 16 hawing a quantum-well structure with a io pair of InGaAs/GaAs, a p-type AlGaAs cladding layer 1 R having a 2N,n~ut files tlxiclulcss, and a p-typo GaAs cap layer 20 having a 0.3~.m film thickness are consecutivexy grown epitaxially O.f this layered structure, the p-type cap layor 20 and the upper portion of p-type cladding layer 18 are formed as a stripe-rs shaped mesa stn~cture having a 4y.m width.
Except for the top of p-type cap layer 2U, a passivation film ZZ inxplemented by an SiN elm is formed on the side walls of the mesa structurE and on the p-type cladding layer 18'.
On top of the exposed p-type cap layer 20 and passivation zo film 22, d p-S7.(1C ClC4lIU(1G 24 iucludiug layered uxetal films of Ti/Pt/Au is formed. On the bottom surface of UaAs substrate 12 is formed an n-side electrode 26 including layered metal fi.lxns cf AuGc/Ni/Au.
.Referring to k'~igs. S,A. to SL, the process of manufacturing the z5 SbUVC-IIICnI,lUIICtI vunveulioual sen~icouductor laser device 10 will ,01- 7-12;16:21 ;~FAX03-6295-0863 ;0362960863 # 6/ 32 be described. Figs. SA to SC arc sectional views of the substrate during the respective steps of the fabrication of the conventional InC~raAs 9SOnm-baud semiconductor laser d~cvicc.
First, on the n-type GaAs substrate 12 are epitaxially formed, s by MOCVD, the z~-type ,~AlGaAs cladding layer 14 hawing 2~,m film thickness, the active layer 1G with the quantum»well structure of the ln(iaAs/(~aA,s pair, the p-type ,AlGaAs cladding layer 18 having 2~.m film thickness, and the p-type GaAs cap layer 2(.1 having 0.3E~,m fi~na. th~ic~css, in the recited order. Thus, the layered structure xs o formed as shown in~ Fig. S,A~.
Then, the p-type cap layer 20 and the upper porkion of p-type cladding layer 18 are etched to form the stripe-shaped mesa structure which is 4~,m in width, a,~ shown in Fib. 5B.
After forming the SiN blm 22 as the passivation film on the i.s entire t~P snrPace of the wafer, the SiN film 22 is rtched tU CxpuSC
the cap layer 20 as shown in Fig. 5C.
The entire top surface of the wafer is then covered with the TiIT~IAu layered metal films by evaporation, thereby forming the p-side electrode 24. The top surface of GaAs substrate 12 is zo pol3sk~ec,1 to have a. thickness of 1 (.1(l~.~m, and thereafter IayerCd mCCdl films of .tluGe/Ni/l1u are evaporated on the entire top surface of the substrate. Thus, the semiconductor laser device 10 can be fabxxcated as shown inn Fig. 4.
In the above-described conventional semiconductor laser z5 IIGVl(;C 10, I,hc band-gap CnCrgy Eg1 of n-type CiraAs substrate 12 is 01- 7-12; 1 6:21 ;~[*F/1X03-6296-0863 ; 0362960863 ~ 6/ 32 1.41 eV and the band-gap energy Eg2 of active layer 16 is 1.27 eV
The relationship EgI>Eg2 enables the light emitted from the active layer to propagate through the substrate.
If the polished bottom surface of Ga,A~s substrate 12 of s semiconductor laser device 14 is nainror-finished, the light that propagated through GaAs substrate 12 is reflected by the bottom surface of the substrate and recombined as reflected light with the light from Lhe ac;live layer, as shov~ru ui Fig. G.
When the reflected light from the bottom surface of the io. substrate combine..s with the light from the active layer, therr arise the following two problems.
The first problem is that a ltink phenomenon appears in the current versus light output characteristic which, as shown in r'ig. 7, adversely affects the linearity of the optical output with respect to is lhc injGClcd currCnl. Such d kink pheuoiueuou makes it ilnpossible to maintain a stable APC (automatic power control) operation.
The seGOnd prohlern is that the influence of the returned light becomes large. As the reflected light ~rorn the bottom surface of the substrate combines with the light from the active layer, ripples zo appear Li the c~nission spect~ru,m at about 3nm intervals, as shown in Fig. g. This is a phenomenon due to the formation of a hybrid resonator formed by an ordinary Fahry-P~rct rescnatcr and 22a and the substrate.
In such a case, a longitudinal mode is selected at a Sam z 5 spaciu~g. As the iu j acted current is varied, the selected wavelength 01- 7-12;16:21 ;;~':FAX03-6296-0863 ;0362960863 # 7/ 32 shifts mainly by the thermal effect while maintaining the 3nm node spacing, thereby varying the output and resulting in a mode hopping noise which is observed as an rxcrssivG noise. The lasiuntg mode becomes a single longitudinal node due to the ripples, so that the s tolerance against the returned light deteriorates_ SUMMARY OF THE INVENTiUhI
Accordingly, it is an object of the invention tc~ pruvidG a~
semiconductor laser device in which the optical output and emission is spectrum are stable with respect to the injected current_ The seittie;ocxductvx laser device according to the present invention is directed to a semiconductor laser device in which an sctive layer having a band-gap CnCrgy Eg2 is epita~ially ,grown on a semiconductor substrate having a band-gap energy Egl, where zs Eg~~Eg2, the device being characterised in that an absorption medium layer for absorbing Iascr light lased by the active layer is formed on the bottom surface of the semiconductor substrate.
The absorption medium layer may be formed nn any manner;
however, it is preferably formed by an alloying reaction between a 2o metal electrode layer fcrn~ed on the bc~ttum surface ur the scmiconduetor substrate and the semiconductor substrate because of the easiness of the process. More specifically, if the semiconductor substrate is a ClaAs substrate, the absorption medium layer formed on the bottom surface of the semiconductor substrate is an lnGaAs 25 layer, wb~~:h is formed by an alloying rGacliun bCLWGCn Iu and C3~aA,s.
O1- 7-12;16:21 ;~'*F~X03-6296-0863 ;03b29608b3 ~ 8/ 32 Namely, the metal electrode layer formed on the bottom surface of the GaA.s substrate includes an xn layer adjacent to the bottom surface of the suhrtrate, and 1hC absorption mcdiu~n layer is an InGaAs layer obtained, after the formation of the metal electrode s layer on the bottom surface of the substrate, by effecting a thermal procxssing Lo alloy the In of the metal electrode layer with the GaA,s of the substrate.
Thus, the semiconductor laser devicx ac;wrding to the present invention has an absorption medium layer formed on the bottom ~o surface of the substrate that absorbs the laser light laced by the active layer. As a result, although the laser light laced by the active layer passes through the semiconductor substrate from the active layer Fide of the substrate surrdce to the bottom surface of the substrate due to the band-gap energy Eg2 of the active Iayer being is smaller than the band-gap enexgy F.g1 of the semic;c~nduclur substrate, the laser light can be absorbed by the absorption medium layer.
Because the amount of laser light reflected by the bottom surface of the semiconductor substrate can thus be reduced in the zo semiconductor laser device according to 1hC iuveuliot~, tl~e linearity of the optical output with respect to the inj ected current can be maintained, the emission spectrum can be stabilized, and the l.a.~ing mode is u~alikely to assume a single longitudinal mode.
2 5 BRIEF DF.SCRTP'TTnN nF THE DRA~V1NGS
01- 7-12;16:21 ;;'(>FAX03-6296-0863 ;0362960863 # 9/ 32 Fig. l is a sectional view showing the structure of a semiconductor laser device according to an embodiment of the invention.
Fig. 2 is a graph showing the injected current versus optienl s output characteristic of the semiconductor device according to the e~nhodi ment_ Fig. 3 is a chart showing the emission spectmxn of the semiconductor laser device according to the embodiment.
Fig. 4 is a sectional view showing a structuxc of a o conventional InGaAs 980nm-band semiconductor lasex device.
Pigs. SA to SC are sectional mews of the substrate during the respective process steps in the manufacture of the conventional InGaAs 980nxn-hand semiconductor laser (ICVl(:C.
Fib. 6 is a schematic view for illustrating laser light ~ s propagating through the substrate and being xef I ected by the bUCLUm suzfacc of the substrate to xccombinc with the laser light from the active layer.
Fig. 7 is a graph showing the injected current vErsus optical output characteristic of the conventional semiconductor laser device.
zo Pig_ 8 is a chart showing the emission spectrum ur the semiconductor laser device according to the embodiment.
PREFERRED EMBODIMENT OF TIC INYENTrON
Specaifically, an embodiment of the present invention wyll be z5 hereunder described ~tx~ detail with referencx to 1hC accUmp~ulyulg 01- 7-12;16:21 ;~ FAX03-5295-0853 ;0352950853 ~V 10/ 32 ' CA 02360441 2001-07-13 a drawings by way of an embodiment thereof.
Referring tc~ Fig. 1, a semiconductor laser device 3f1 according to the present embodiment includes an n-type GaAs substrate 32 having a thickness of about 100,um and a bandgap energy Eg1 of 1.41e'V', a~~d a layer structure includuig: au c~-type AlGaAs cladding layer 34 having a 2~am film thickness; an active layer 3f~ having a qnanfimt-well structure including two l.ayexs of InGaAs/GaAs and having a bandgap energy Eg2 of l.ZtxV, which is smaller than that of n-type GaAs substrate 32; a p-type AIGaAs .
io cladding layer 38 having a 2~n~. fiLux thiclwess; a~xd a p-type Ga,As cap layer 40 having a U.3,unz film thicl~ness, which axe wnsecutively epitaxially-grown on the substrate.
The p-type cap layer 40 and an upper portion of p-type cladding layer 38 are formed as a stripe-shaped mesa stn~cture 15 having a width of 4,um.
A passivation elm 42 made of SiN is formed on the sides of the mesa structure and on the p-type cXaddiu~g layer 38 except fox the top surface of the p-type cap layer 4U. A p-side electrode 44 including layered metal films of 'I~/Pt/Au is formed nn the exposed ao p-type cap layer 40 and the passivation Xay~x 42.
On the bottom surface of n-type GaAs substrate 32 is formed an n-side electrode 4G includW g layored metaX filc~~s of ln/AuGe/Ni/Au. An InGaAs layer X1.13 is interposed between the re-type CTa,A,.s substrate 3~ and the n-side electrode 46 as the absorption a3 medium layer for absorbing the laser light with the emission 01- 7-12;16:21 ;;~>FAX03-6296-0863 ;0362960863 # 11/ 32 wavElcagth of the active layer 36.
'x'he semiconductor laser device 30 according to the present CmbodimGnt eau be mauufacturcd, siunilarly to the conventional process, by using a MOCVD technique, for example, to form: the n-s type AIGaAs cladding layer 44 having a 2,um ~1m thicl~nesc; the active layer 3G with the two-layer quantum well structure of lnC~aAs/(SraAs; the p-type AIGaAs cladding layer 38 having a 2,um elm thickne~.~; and the p-type C'taA~~ cap layer 40 having a O.3,utll film thickness, which arc consecutively grown on the n-type C~aAs io substrate 32 to form tl~e layered strucri~re.
Thereafter, the p-type cap layer 40 and the upper portion of p-type cladding layer 38 are etched to form the 4 ,um-wide stripe-shapcd mrsa slructu.ie. 'The SiN fil~x~ 42 as the passivation ~lxn is then formed on the entire upper su~xface of the substrate, and the SiN
a. s filtx~ 42 is etched to expose the p-typC c;rdp ldyGr 40.
Then, the layered metal. films of TilPt/Au are evaporated on the entire upper surface of the substrate, thereby foxaning the r-side electrode 24. The bottom surface of GaAs substrate 32 is polished to have a thickness of 100,ccm.
~o SubsequGnlly, in lhG mauurac;lure of the sc~tuico~tlductor laser device 30 according to the present embodiment, metal films of In/AuGe/Ni/Au are sequentially evaporated on the hotto~x~. surface of the substxatc, thereby forming the n~sidc electrode 46 composed of the layered metal ~Lms.
25 ThC sub5lrale vn which the u-side elcctxodc 4G is formed is O1- 7-12;16:21 ;;~>FAX03-6296-0863 ;0362960863 t~ 12/ 32 l~
then subjected to a heat processing at a tcnnpcraturc of 350~C in a hydrogen ambient for S minutes. 'This causes an alloying reaction to take Place between In co the layGrCd mGldl filtus forming the n-side electrode 46 and Ga,A,s of the n-type GaAs substrate 32. As a s result, the InGaAs layer 48 having a film thiclcn.ess of about 100nm can be 'rUrmCd bCtWeen the n-side electrode 4G and the n-type GaAs substrate 32.
In the semiconductor laser device 3n according to the present embodiment, the InCaAs layer 48 is formed on the bottom su~ace 0 of ntype GaAs substrate 32 so that the InGaAs layer 48 serves as the avsorpliomuerlituu for the 980mu emission wavelength and has a band-gap energy L~'g3 of about 0.9e V
Although the lasCr light with the cmissiott wavelength 980nm laced by the active layer 36 passes through the n-type CiaAs 15 substrate 32 towards the bottom surface cf the Substrate Prom ihC
active-layer side of the substrate, the passed laser light is absorbed by the InGaAs layer 48 before reaching the bottom surface of the substrate to be reflected, because the bandgap cx~crgy Eg2 of the active layer 36 is smaller than the bandgap energy Egl of the n-type Z o GaAs subsixate 32.
Thus, the amount of laser light reflected by the bottom surface of the n-type GaAs substrate 32 is reduced in the present elubodinaeut. Accordingly, the linearity of the optical output with respect to the injected current can be maintained, the emission zs spectarnm is ctahili~ed, and the lacing modC is unlikely to assut~ie a 01- 7-12;16:21 ;;~'7FAX03-5295-0853 ;0352950853 ~ 13/ 32 single longitudinal anode.
A,n actual sample of the semiconductor laser devicx 3(I
according to the present embodiment was fabricated and subjected to the measurement of current versus optical output characteristic.
s The measurement of the dCVI~:C CXhI~ILCd ~la~ curretlt versus optical output charactcr~istic was linear without kinks up to an injected current of 300mA, as shown in Fi~g_ 2_ T1,'~e cniission spectrum of the sample was observed to have no ripples as shown in F'ig. 3, thereby confirming a longitudinal ~.c~ multimode lacing operation.
Although the present embodiment was described for the 980nm-band laser, similar advantageo~tys effects can he expec,-ted fmrn lasers including active layers having band-gap wavelengths ranging from 1-3~Cm bands (such as those with an active layer i5 ituplou~entcd by rnC~aNAs).
FIELD OF THE INVENTION' s Tile present i~ivel~t.ion relates to a semiconductor laser device, and more particularly to a semiconductor Iaser device which has a linear ch2racteristic between injected current and oplic;al output and achieves a stable oscillating spectrum, and which is particularly suitable for applications in optical communications.
io BACKGROUND UF' THE 1NV~.N'1'.IUN
Semiec~nductor laser devic;GS are commonly used for applications in. optical communications. In particular, InGaAs 980nm-band semiconductor laser devices axe frequently used as the s pumping light source for optical amplifiexs in optical fiber communication systems.
The setuicouductor laser device for use as the pumping light source for the optical amplifier, for example, is required to have a stable optical outPnt and emission spec.~trum with rCSpec:l to the Z o inj ccted current.
Specifically, the current versus light output characteristic is IC(~uICCCl to be linear iu older to iiicr case the reliability of the optical amplification operation, for example. It is also preferable that the emission spectrum is in the stable longitudinal multimode lacing 'for as suppressing the influence of returned li,~ht.
,01- 7-12;16:21 ;~ FAX03-5296-0963 ;0362960863 # 4/ 32 Referring to Fig. 4, the structure of a conventional InGaAs 980nm-band semiconductor laser device will be described. Fig. 4 is a sectional vices sliowi~xg tlxc structure of the conventional InGaAs ~SOnm-band senuiconductor laser device.
s As shown in Fig. 4, the conventional TnCTa,A.s 9ROnm-hand semiconductor laser device 10 has a layered structure including an n-type GaAs substrate 12 having a thickness of 100E.irn. On the substrate, an n-type AIGaAs cladding layer 14 having a 2Nan film thickness, an active layer 16 hawing a quantum-well structure with a io pair of InGaAs/GaAs, a p-type AlGaAs cladding layer 1 R having a 2N,n~ut files tlxiclulcss, and a p-typo GaAs cap layer 20 having a 0.3~.m film thickness are consecutivexy grown epitaxially O.f this layered structure, the p-type cap layor 20 and the upper portion of p-type cladding layer 18 are formed as a stripe-rs shaped mesa stn~cture having a 4y.m width.
Except for the top of p-type cap layer 2U, a passivation film ZZ inxplemented by an SiN elm is formed on the side walls of the mesa structurE and on the p-type cladding layer 18'.
On top of the exposed p-type cap layer 20 and passivation zo film 22, d p-S7.(1C ClC4lIU(1G 24 iucludiug layered uxetal films of Ti/Pt/Au is formed. On the bottom surface of UaAs substrate 12 is formed an n-side electrode 26 including layered metal fi.lxns cf AuGc/Ni/Au.
.Referring to k'~igs. S,A. to SL, the process of manufacturing the z5 SbUVC-IIICnI,lUIICtI vunveulioual sen~icouductor laser device 10 will ,01- 7-12;16:21 ;~FAX03-6295-0863 ;0362960863 # 6/ 32 be described. Figs. SA to SC arc sectional views of the substrate during the respective steps of the fabrication of the conventional InC~raAs 9SOnm-baud semiconductor laser d~cvicc.
First, on the n-type GaAs substrate 12 are epitaxially formed, s by MOCVD, the z~-type ,~AlGaAs cladding layer 14 hawing 2~,m film thickness, the active layer 1G with the quantum»well structure of the ln(iaAs/(~aA,s pair, the p-type ,AlGaAs cladding layer 18 having 2~.m film thickness, and the p-type GaAs cap layer 2(.1 having 0.3E~,m fi~na. th~ic~css, in the recited order. Thus, the layered structure xs o formed as shown in~ Fig. S,A~.
Then, the p-type cap layer 20 and the upper porkion of p-type cladding layer 18 are etched to form the stripe-shaped mesa structure which is 4~,m in width, a,~ shown in Fib. 5B.
After forming the SiN blm 22 as the passivation film on the i.s entire t~P snrPace of the wafer, the SiN film 22 is rtched tU CxpuSC
the cap layer 20 as shown in Fig. 5C.
The entire top surface of the wafer is then covered with the TiIT~IAu layered metal films by evaporation, thereby forming the p-side electrode 24. The top surface of GaAs substrate 12 is zo pol3sk~ec,1 to have a. thickness of 1 (.1(l~.~m, and thereafter IayerCd mCCdl films of .tluGe/Ni/l1u are evaporated on the entire top surface of the substrate. Thus, the semiconductor laser device 10 can be fabxxcated as shown inn Fig. 4.
In the above-described conventional semiconductor laser z5 IIGVl(;C 10, I,hc band-gap CnCrgy Eg1 of n-type CiraAs substrate 12 is 01- 7-12; 1 6:21 ;~[*F/1X03-6296-0863 ; 0362960863 ~ 6/ 32 1.41 eV and the band-gap energy Eg2 of active layer 16 is 1.27 eV
The relationship EgI>Eg2 enables the light emitted from the active layer to propagate through the substrate.
If the polished bottom surface of Ga,A~s substrate 12 of s semiconductor laser device 14 is nainror-finished, the light that propagated through GaAs substrate 12 is reflected by the bottom surface of the substrate and recombined as reflected light with the light from Lhe ac;live layer, as shov~ru ui Fig. G.
When the reflected light from the bottom surface of the io. substrate combine..s with the light from the active layer, therr arise the following two problems.
The first problem is that a ltink phenomenon appears in the current versus light output characteristic which, as shown in r'ig. 7, adversely affects the linearity of the optical output with respect to is lhc injGClcd currCnl. Such d kink pheuoiueuou makes it ilnpossible to maintain a stable APC (automatic power control) operation.
The seGOnd prohlern is that the influence of the returned light becomes large. As the reflected light ~rorn the bottom surface of the substrate combines with the light from the active layer, ripples zo appear Li the c~nission spect~ru,m at about 3nm intervals, as shown in Fig. g. This is a phenomenon due to the formation of a hybrid resonator formed by an ordinary Fahry-P~rct rescnatcr and 22a and the substrate.
In such a case, a longitudinal mode is selected at a Sam z 5 spaciu~g. As the iu j acted current is varied, the selected wavelength 01- 7-12;16:21 ;;~':FAX03-6296-0863 ;0362960863 # 7/ 32 shifts mainly by the thermal effect while maintaining the 3nm node spacing, thereby varying the output and resulting in a mode hopping noise which is observed as an rxcrssivG noise. The lasiuntg mode becomes a single longitudinal node due to the ripples, so that the s tolerance against the returned light deteriorates_ SUMMARY OF THE INVENTiUhI
Accordingly, it is an object of the invention tc~ pruvidG a~
semiconductor laser device in which the optical output and emission is spectrum are stable with respect to the injected current_ The seittie;ocxductvx laser device according to the present invention is directed to a semiconductor laser device in which an sctive layer having a band-gap CnCrgy Eg2 is epita~ially ,grown on a semiconductor substrate having a band-gap energy Egl, where zs Eg~~Eg2, the device being characterised in that an absorption medium layer for absorbing Iascr light lased by the active layer is formed on the bottom surface of the semiconductor substrate.
The absorption medium layer may be formed nn any manner;
however, it is preferably formed by an alloying reaction between a 2o metal electrode layer fcrn~ed on the bc~ttum surface ur the scmiconduetor substrate and the semiconductor substrate because of the easiness of the process. More specifically, if the semiconductor substrate is a ClaAs substrate, the absorption medium layer formed on the bottom surface of the semiconductor substrate is an lnGaAs 25 layer, wb~~:h is formed by an alloying rGacliun bCLWGCn Iu and C3~aA,s.
O1- 7-12;16:21 ;~'*F~X03-6296-0863 ;03b29608b3 ~ 8/ 32 Namely, the metal electrode layer formed on the bottom surface of the GaA.s substrate includes an xn layer adjacent to the bottom surface of the suhrtrate, and 1hC absorption mcdiu~n layer is an InGaAs layer obtained, after the formation of the metal electrode s layer on the bottom surface of the substrate, by effecting a thermal procxssing Lo alloy the In of the metal electrode layer with the GaA,s of the substrate.
Thus, the semiconductor laser devicx ac;wrding to the present invention has an absorption medium layer formed on the bottom ~o surface of the substrate that absorbs the laser light laced by the active layer. As a result, although the laser light laced by the active layer passes through the semiconductor substrate from the active layer Fide of the substrate surrdce to the bottom surface of the substrate due to the band-gap energy Eg2 of the active Iayer being is smaller than the band-gap enexgy F.g1 of the semic;c~nduclur substrate, the laser light can be absorbed by the absorption medium layer.
Because the amount of laser light reflected by the bottom surface of the semiconductor substrate can thus be reduced in the zo semiconductor laser device according to 1hC iuveuliot~, tl~e linearity of the optical output with respect to the inj ected current can be maintained, the emission spectrum can be stabilized, and the l.a.~ing mode is u~alikely to assume a single longitudinal mode.
2 5 BRIEF DF.SCRTP'TTnN nF THE DRA~V1NGS
01- 7-12;16:21 ;;'(>FAX03-6296-0863 ;0362960863 # 9/ 32 Fig. l is a sectional view showing the structure of a semiconductor laser device according to an embodiment of the invention.
Fig. 2 is a graph showing the injected current versus optienl s output characteristic of the semiconductor device according to the e~nhodi ment_ Fig. 3 is a chart showing the emission spectmxn of the semiconductor laser device according to the embodiment.
Fig. 4 is a sectional view showing a structuxc of a o conventional InGaAs 980nm-band semiconductor lasex device.
Pigs. SA to SC are sectional mews of the substrate during the respective process steps in the manufacture of the conventional InGaAs 980nxn-hand semiconductor laser (ICVl(:C.
Fib. 6 is a schematic view for illustrating laser light ~ s propagating through the substrate and being xef I ected by the bUCLUm suzfacc of the substrate to xccombinc with the laser light from the active layer.
Fig. 7 is a graph showing the injected current vErsus optical output characteristic of the conventional semiconductor laser device.
zo Pig_ 8 is a chart showing the emission spectrum ur the semiconductor laser device according to the embodiment.
PREFERRED EMBODIMENT OF TIC INYENTrON
Specaifically, an embodiment of the present invention wyll be z5 hereunder described ~tx~ detail with referencx to 1hC accUmp~ulyulg 01- 7-12;16:21 ;~ FAX03-5295-0853 ;0352950853 ~V 10/ 32 ' CA 02360441 2001-07-13 a drawings by way of an embodiment thereof.
Referring tc~ Fig. 1, a semiconductor laser device 3f1 according to the present embodiment includes an n-type GaAs substrate 32 having a thickness of about 100,um and a bandgap energy Eg1 of 1.41e'V', a~~d a layer structure includuig: au c~-type AlGaAs cladding layer 34 having a 2~am film thickness; an active layer 3f~ having a qnanfimt-well structure including two l.ayexs of InGaAs/GaAs and having a bandgap energy Eg2 of l.ZtxV, which is smaller than that of n-type GaAs substrate 32; a p-type AIGaAs .
io cladding layer 38 having a 2~n~. fiLux thiclwess; a~xd a p-type Ga,As cap layer 40 having a U.3,unz film thicl~ness, which axe wnsecutively epitaxially-grown on the substrate.
The p-type cap layer 40 and an upper portion of p-type cladding layer 38 are formed as a stripe-shaped mesa stn~cture 15 having a width of 4,um.
A passivation elm 42 made of SiN is formed on the sides of the mesa structure and on the p-type cXaddiu~g layer 38 except fox the top surface of the p-type cap layer 4U. A p-side electrode 44 including layered metal films of 'I~/Pt/Au is formed nn the exposed ao p-type cap layer 40 and the passivation Xay~x 42.
On the bottom surface of n-type GaAs substrate 32 is formed an n-side electrode 4G includW g layored metaX filc~~s of ln/AuGe/Ni/Au. An InGaAs layer X1.13 is interposed between the re-type CTa,A,.s substrate 3~ and the n-side electrode 46 as the absorption a3 medium layer for absorbing the laser light with the emission 01- 7-12;16:21 ;;~>FAX03-6296-0863 ;0362960863 # 11/ 32 wavElcagth of the active layer 36.
'x'he semiconductor laser device 30 according to the present CmbodimGnt eau be mauufacturcd, siunilarly to the conventional process, by using a MOCVD technique, for example, to form: the n-s type AIGaAs cladding layer 44 having a 2,um ~1m thicl~nesc; the active layer 3G with the two-layer quantum well structure of lnC~aAs/(SraAs; the p-type AIGaAs cladding layer 38 having a 2,um elm thickne~.~; and the p-type C'taA~~ cap layer 40 having a O.3,utll film thickness, which arc consecutively grown on the n-type C~aAs io substrate 32 to form tl~e layered strucri~re.
Thereafter, the p-type cap layer 40 and the upper portion of p-type cladding layer 38 are etched to form the 4 ,um-wide stripe-shapcd mrsa slructu.ie. 'The SiN fil~x~ 42 as the passivation ~lxn is then formed on the entire upper su~xface of the substrate, and the SiN
a. s filtx~ 42 is etched to expose the p-typC c;rdp ldyGr 40.
Then, the layered metal. films of TilPt/Au are evaporated on the entire upper surface of the substrate, thereby foxaning the r-side electrode 24. The bottom surface of GaAs substrate 32 is polished to have a thickness of 100,ccm.
~o SubsequGnlly, in lhG mauurac;lure of the sc~tuico~tlductor laser device 30 according to the present embodiment, metal films of In/AuGe/Ni/Au are sequentially evaporated on the hotto~x~. surface of the substxatc, thereby forming the n~sidc electrode 46 composed of the layered metal ~Lms.
25 ThC sub5lrale vn which the u-side elcctxodc 4G is formed is O1- 7-12;16:21 ;;~>FAX03-6296-0863 ;0362960863 t~ 12/ 32 l~
then subjected to a heat processing at a tcnnpcraturc of 350~C in a hydrogen ambient for S minutes. 'This causes an alloying reaction to take Place between In co the layGrCd mGldl filtus forming the n-side electrode 46 and Ga,A,s of the n-type GaAs substrate 32. As a s result, the InGaAs layer 48 having a film thiclcn.ess of about 100nm can be 'rUrmCd bCtWeen the n-side electrode 4G and the n-type GaAs substrate 32.
In the semiconductor laser device 3n according to the present embodiment, the InCaAs layer 48 is formed on the bottom su~ace 0 of ntype GaAs substrate 32 so that the InGaAs layer 48 serves as the avsorpliomuerlituu for the 980mu emission wavelength and has a band-gap energy L~'g3 of about 0.9e V
Although the lasCr light with the cmissiott wavelength 980nm laced by the active layer 36 passes through the n-type CiaAs 15 substrate 32 towards the bottom surface cf the Substrate Prom ihC
active-layer side of the substrate, the passed laser light is absorbed by the InGaAs layer 48 before reaching the bottom surface of the substrate to be reflected, because the bandgap cx~crgy Eg2 of the active layer 36 is smaller than the bandgap energy Egl of the n-type Z o GaAs subsixate 32.
Thus, the amount of laser light reflected by the bottom surface of the n-type GaAs substrate 32 is reduced in the present elubodinaeut. Accordingly, the linearity of the optical output with respect to the injected current can be maintained, the emission zs spectarnm is ctahili~ed, and the lacing modC is unlikely to assut~ie a 01- 7-12;16:21 ;;~'7FAX03-5295-0853 ;0352950853 ~ 13/ 32 single longitudinal anode.
A,n actual sample of the semiconductor laser devicx 3(I
according to the present embodiment was fabricated and subjected to the measurement of current versus optical output characteristic.
s The measurement of the dCVI~:C CXhI~ILCd ~la~ curretlt versus optical output charactcr~istic was linear without kinks up to an injected current of 300mA, as shown in Fi~g_ 2_ T1,'~e cniission spectrum of the sample was observed to have no ripples as shown in F'ig. 3, thereby confirming a longitudinal ~.c~ multimode lacing operation.
Although the present embodiment was described for the 980nm-band laser, similar advantageo~tys effects can he expec,-ted fmrn lasers including active layers having band-gap wavelengths ranging from 1-3~Cm bands (such as those with an active layer i5 ituplou~entcd by rnC~aNAs).
Claims (4)
1. A semiconductor laser device comprising an active layer having a bandgap energy Eg2 and epitaxially grown on a semiconductor substrate having a bandgap energy Eg1, wherein Eg1 > Eg2, characterized in that an absorption medium layer for absorbing laser light emitted by the active layer is formed on a bottom surface of the semiconductor substrate.
2. The semiconductor laser device according to claim 1, wherein the absorption medium layer is formed by an alloying reaction between a metal electrode layer formed on the bottom surface of the substrate and the semiconductor substrate.
3. The semiconductor laser device according to claim 1 or 2, wherein the semiconductor substrate is a GaAs substrate and the absorption medium layer is an InGaAs layer.
4. The semiconductor laser device according to claim 3, wherein the metal electrode layer formed on the bottom surface of the GaAs substrate includes an In layer in contact with the bottom surface of the substrate, and wherein the absorption medium layer is an InGaAs layer formed by a heat processing for alloying the In of the metal electrode layer with the GaAs of the GaAs substrate after forming the metal electrode layer un the bottom surface of the substrate.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP11-325223 | 1999-11-16 | ||
| JP32522399A JP4043672B2 (en) | 1999-11-16 | 1999-11-16 | Semiconductor laser element |
| PCT/JP2000/008067 WO2001037387A1 (en) | 1999-11-16 | 2000-11-16 | Semiconductor laser |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2360441A1 true CA2360441A1 (en) | 2001-05-25 |
Family
ID=18174408
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002360441A Abandoned CA2360441A1 (en) | 1999-11-16 | 2000-11-16 | Semiconductor laser device |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US6738405B1 (en) |
| EP (1) | EP1152505A4 (en) |
| JP (1) | JP4043672B2 (en) |
| CA (1) | CA2360441A1 (en) |
| WO (1) | WO2001037387A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2009182145A (en) | 2008-01-30 | 2009-08-13 | Sumitomo Electric Ind Ltd | Semiconductor optical element |
| JP2010021430A (en) | 2008-07-11 | 2010-01-28 | Sumitomo Electric Ind Ltd | Semiconductor photonic element |
| US20190229496A1 (en) * | 2016-07-27 | 2019-07-25 | Sony Corporation | Nitride semiconductor laser and electronic apparatus |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3984261A (en) * | 1974-06-10 | 1976-10-05 | Rca Corporation | Ohmic contact |
| DE3280183D1 (en) * | 1981-11-30 | 1990-06-28 | Fujitsu Ltd | OPTICAL SEMICONDUCTOR ARRANGEMENT. |
| JPS60241283A (en) * | 1984-05-16 | 1985-11-30 | Toshiba Corp | Integrated chemical semiconductor element |
| JPH07240561A (en) * | 1994-02-23 | 1995-09-12 | Hewlett Packard Co <Hp> | Ii-vi family system semiconductor laser and its preparation |
| US5606572A (en) * | 1994-03-24 | 1997-02-25 | Vixel Corporation | Integration of laser with photodiode for feedback control |
| US5491712A (en) * | 1994-10-31 | 1996-02-13 | Lin; Hong | Integration of surface emitting laser and photodiode for monitoring power output of surface emitting laser |
| JPH08279650A (en) * | 1995-04-06 | 1996-10-22 | Mitsubishi Electric Corp | Semiconductor laser and manufacture thereof |
| JPH10321945A (en) * | 1997-05-19 | 1998-12-04 | Mitsubishi Electric Corp | Semiconductor laser device and its manufacture |
| US5943357A (en) * | 1997-08-18 | 1999-08-24 | Motorola, Inc. | Long wavelength vertical cavity surface emitting laser with photodetector for automatic power control and method of fabrication |
| JP4196439B2 (en) * | 1998-08-27 | 2008-12-17 | ソニー株式会社 | Semiconductor light emitting device and manufacturing method thereof |
-
1999
- 1999-11-16 JP JP32522399A patent/JP4043672B2/en not_active Expired - Fee Related
-
2000
- 2000-11-16 EP EP00976276A patent/EP1152505A4/en not_active Withdrawn
- 2000-11-16 WO PCT/JP2000/008067 patent/WO2001037387A1/en not_active Application Discontinuation
- 2000-11-16 US US09/889,596 patent/US6738405B1/en not_active Expired - Fee Related
- 2000-11-16 CA CA002360441A patent/CA2360441A1/en not_active Abandoned
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| Publication number | Publication date |
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| JP4043672B2 (en) | 2008-02-06 |
| EP1152505A1 (en) | 2001-11-07 |
| US6738405B1 (en) | 2004-05-18 |
| JP2001144371A (en) | 2001-05-25 |
| WO2001037387A1 (en) | 2001-05-25 |
| EP1152505A4 (en) | 2005-11-23 |
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