WO2006030845A1 - Iii族窒化物半導体光素子 - Google Patents
Iii族窒化物半導体光素子 Download PDFInfo
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- WO2006030845A1 WO2006030845A1 PCT/JP2005/017007 JP2005017007W WO2006030845A1 WO 2006030845 A1 WO2006030845 A1 WO 2006030845A1 JP 2005017007 W JP2005017007 W JP 2005017007W WO 2006030845 A1 WO2006030845 A1 WO 2006030845A1
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- nitride semiconductor
- iii nitride
- optical device
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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
- H01S5/32—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures
- H01S5/323—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
- H01S5/32308—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser emitting light at a wavelength less than 900 nm
- H01S5/32341—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser emitting light at a wavelength less than 900 nm blue laser based on GaN or GaP
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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
- H01S5/223—Buried stripe structure
Definitions
- the present invention relates to an in-group nitride semiconductor optical device.
- Group III nitride semiconductors typified by gallium nitride, are highly regarded as materials for light emitting diodes (LEDs) and laser diodes (1 aser diodes, LDs) because of their high-efficiency blue-violet emission. Have been bathed.
- LEDs light emitting diodes
- LDs laser diodes
- LD is expected as a light source for large-capacity optical disk devices, and in recent years, development of high-power LD as a light source for writing has been energetically advanced.
- Fig. 1 shows a typical structure of a nitride blue-violet LD.
- the ridge 101 is formed by dry etching.
- the upper portion of the ridge is covered with an insulating film 102 having a striped opening, and a p-type electrode 103 is provided in the opening.
- Current confinement is done with striped electrodes, and the transverse mode is controlled by adjusting the ridge width and ridge height.
- a ridge type semiconductor laser has the following problems.
- the ridge width needs to be narrowed to about 1.7 / z m for the high output blue LD.
- the electrode area is also narrowed, which increases the contact resistance.
- the operating current density is also high, so the element may deteriorate due to heat generated at the contacts.
- an inner stripe type LD using A1N or (Al) GaN as a current confinement layer as shown in FIG. 2 has been proposed (Japanese Patent Laid-Open No. 2001-15860, Japanese Patent Laid-Open 10-0931 92, JP 2003-78215). Since these inner stripe LDs have a large contact area, a low contact resistance can be realized even in a high output LD with a narrow stripe width. In particular, an inner 1 'stripe using low temperature growth A1N as the current confinement layer The structure (Japanese Patent Laid-Open No. 2001-15860) is expected to be a low-voltage operation and high-power LD because it has the advantage that damage is less affected by impurity contamination during the opening of the current confinement layer.
- the device in an inner 'striped LD using AlGaN or A1N as the current confinement layer, the device may be destroyed in processes such as device separation, wire bonding, and heat fusion. In this respect, there was room for improvement.
- the present invention has been made in view of the above circumstances, and specifically has the following configuration.
- the semiconductor laser according to the first aspect of the present invention includes:
- a current confinement layer provided on the active layer
- a current injection opening provided in the current confinement layer, a clad layer having a superlattice structure provided above the current confinement layer and the current injection opening,
- a contact layer provided on top of the cladding layer
- An electrode provided on the surface of the contact layer
- the dislocation density of the cladding layer in the region immediately above the current confinement layer is greater than the dislocation density of the cladding layer in the region immediately above the opening for current injection;
- the semiconductor optical device of the present invention employs a clad layer having a superlattice structure. Since carriers are induced at the interface of each layer constituting the superlattice structure, the resistance in the layer thickness direction is reduced and the carrier mobility in the layer surface direction is increased. As a result, carriers can be efficiently used for device operation, and the operating voltage can be greatly reduced.
- the dislocation density of the cladding layer has a distribution over the region immediately above the current confinement layer and the region immediately above the current injection opening (current injection region).
- current injection region the region immediately above the current injection opening
- the dislocation density of the cladding layer is increased to reduce carrier mobility and prevent leakage of carriers into this region.
- the current injection efficiency is improved, and for example, the threshold current in the semiconductor laser is reduced.
- a current confinement layer provided on the active layer
- a current injection opening provided in the current confinement layer, a clad layer having a superlattice structure provided above the current confinement layer and the current injection opening,
- a contact layer provided on top of the cladding layer
- An electrode provided on the surface of the contact layer
- the current confinement layer is composed of AlGaIn__N (0.4 ⁇ x ⁇ l, 0 ⁇ y ⁇ 0.6, 0 ⁇ x + y ⁇ l)
- a semiconductor laser according to a third aspect of the present invention includes:
- a current confinement layer provided on the active layer
- a current injection opening provided in the current confinement layer, a clad layer having a superlattice structure provided above the current confinement layer and the current injection opening,
- a contact layer provided on top of the cladding layer
- An electrode provided in contact with the contact layer exposed in the opening
- the current injection opening in the current injection region has a stripe shape
- the current confinement layer is composed of a pair of stripe-shaped current confinement layers provided on both sides of the stripe-shaped current injection opening.
- the current confinement layer uses a material having a composition different from that of the surrounding semiconductor, distortion or stress due to a difference in lattice constant or the like is generated at the interface between the current confinement layer and another semiconductor layer. Therefore, in the present invention, a pair of stripe-shaped current confinement layers provided on both sides of the current injection region (stripe-shaped current injection opening) is solved. According to such a configuration, the coverage of the underlayer by the current confinement layer can be reduced, distortion and stress can be effectively reduced, and good current injection efficiency can be realized.
- the end of the opening of the insulating layer is positioned above the current confinement layer.
- the current confinement layer is desired to have as low a coverage ratio as possible to the underlayer (active layer) within a range that maintains its function.
- leakage of carriers injected from the electrode cap becomes a problem.
- a current confinement layer is provided around the current injection region (stripe-shaped current injection opening) and no current confinement layer is provided in the outer region, the distortion
- carrier leakage (current leakage) in the outer region of the stripe-shaped current confinement layer becomes a problem.
- the insulating layer is disposed above the outer region where the current confinement layer is not provided, and current is injected into the outer region where the current confinement layer is not provided.
- the structure which is not done is realized. As a result, it is possible to suppress the generation of distortion due to the current confinement layer and realize a good current injection efficiency.
- the coverage ratio of the current confinement layer to the underlayer (active layer) is preferably 50% or less, more preferably 20% or less.
- the semiconductor laser according to the first embodiment of the present invention employs a cladding layer having a superlattice structure, and the dislocation density of the superlattice cladding layer in the region immediately above the current confinement layer is Since the structure is higher than the dislocation density of the supers cladding layer in the region immediately above the current injection opening provided in the current confinement layer, good current injection efficiency can be stably obtained.
- the semiconductor laser according to the second embodiment of the present invention uses a clad layer having a superlattice structure and a current confinement layer composed of AlGaInN having a high A1 composition. Therefore, good current injection efficiency can be stably obtained.
- an insulating layer having an opening is provided on the surface of the contact layer, and a pair of current injection regions (stripe-shaped current injection openings) are provided on both sides. Since the stripe-shaped current confinement layer is provided, good current injection efficiency can be realized while suppressing the occurrence of distortion due to the current confinement layer.
- FIG. 1 is a cross-sectional view schematically showing the structure of a conventional semiconductor laser having a ridge-type waveguide structure.
- FIG. 2 is a cross-sectional view schematically showing the structure of a conventional inner'striped semiconductor laser.
- FIG. 3 is a cross-sectional view schematically showing the structure of an inner stripe semiconductor laser according to the first embodiment of the present invention.
- FIG. 4 is a cross-sectional view schematically showing the structure of an inner stripe type semiconductor laser according to a second embodiment of the present invention.
- FIG. 5 is a cross-sectional view schematically showing the structure of an inner stripe semiconductor laser according to a third embodiment of the present invention.
- the semiconductors lasers 1 type 1 0 & ⁇ on the third substrate 301, over-flop 11 Type 0 & ⁇ layer 302 (31 concentration 4 10 17 (-?? 111 _ 3 , Thickness: m), Si-doped n-type AlGaN (Si concentration 4 X 10 cm, thickness 2 m)
- N-type cladding layer 303 Si-doped n-type GaN (Si concentration 4 X 10 17 cm _3 , thickness 0.1 ⁇ m) n-type optical confinement layer 304, InGaN (thickness 3 nm) well layer Si-doped In Ga
- ⁇ -type clad layer 309 with a superlattice structure (total thickness 0.65 m) with a periodic structural force of 309, Mg-doped p-type GaN (Mg concentration 1 X 10 2 ° cm " 3 , thickness 0.02 ⁇ m) force p-type contact layer 3 10 is laminated
- the upper surface of p-type contact layer 310 is a flat surface, and the upper part of this laminated structure (the upper part of P-type contact layer 310)
- a p-type electrode 311 and an n-type electrode 312 are provided below the n-type GaN substrate 301, respectively.
- the current confinement layer 308 serves to prevent current from flowing in the layer thickness direction.
- the current confinement layer 308 can be made of a material having a higher resistance than the p-type cladding layer 309, for example.
- the high resistance material used for the current confinement layer 308 is Al Ga In with a high A1 composition.
- N can be used.
- X is preferably 0.4 or more, especially A1N
- the thickness of the current confinement layer 308 is preferably selected in the range of 50 nm to 200 nm. In this way, for example, a heterojunction having a valence band discontinuity ⁇ ⁇ is formed at each interface of the superlattice p-type cladding layer 309Z current constriction layer 308ZP-type GaN guide layer 307. Therefore, a reliable current blocking effect can be obtained. If Al Ga In N with a high A1 composition is used for the current confinement layer 308, the refractive index of the current confinement layer 308 is that of the p-type GaN guide layer 307 and that of the p-type clad layer 309 of the superlattice structure.
- the refractive index of the active layer is n
- the refractive index of the light guide layer is n
- the refractive index of the cladding layer is n
- the refractive index of the current confinement layer is n
- n> n> n for example, ⁇ — ⁇ 0 ⁇ 06, ⁇ — ⁇ 0
- an insulating material having a refractive index smaller than that of Al Ga In N having a high A1 composition such as silicon oxide and silicon nitride, can also be used as a constituent material of the current confinement layer 308.
- the current confinement layer 308 is made to have a reverse conductivity type (in this embodiment, n-type) with the p-type cladding layer 309 and a pn junction is formed at the interface between them, that is, the p-type GaN guide layer 307Z current
- the constriction layer 308ZP type clad layer 309 may have a pnp structure to prevent current from flowing.
- oxygen, selenium, or sulfur is preferably used as an impurity introduced into the current confinement layer 308.
- the p-type cladding layer 309 is a superlattice structure in which GaN layers and AlGaN layers are alternately stacked.
- the number of periods of the superlattice is at least 50 periods, more preferably 140 periods or more. In this embodiment, it is 130 periods.
- the operating voltage is significantly reduced.
- the superlattice structure layer does not have to be in direct contact with the p-side guide layer 307 and the p-contact layer 310. This is desirable. It is assumed that the p-type cladding layer including the superlattice structure is thicker than the current confinement layer 308.
- the thickness of the superlattice structure layer included in the p-type cladding layer 309 may be larger than the thickness of the current confinement layer 308. It is more desirable in terms of crack suppression and voltage reduction.
- the p-type cladding layer 309 has a portion with a high dislocation density and a portion with a low dislocation density. That is, in the region immediately above the current confinement layer 308, the dislocation density is relatively low in the region immediately above the current injection opening provided in the current confinement layer 308, where the dislocation density is relatively high. Yes. In this embodiment, the dislocation density in the region immediately above the current confinement layer 308 is 100 times or more the dislocation density in the region immediately above the current injection opening provided in the current confinement layer 308.
- Such a structure can be realized by appropriately selecting the composition and deposition conditions of the current confinement layer 308 and the growth conditions (deposition rate, VZIII ratio, etc.) of the p-type cladding layer 309.
- the semiconductor laser according to the present embodiment since the p-type cladding layer 309 has a superlattice structure, resistance in the layer thickness direction is reduced and carrier mobility in the layer surface direction is increased. In other words, in the GaN / AlGaN superlattice structure, holes are induced in the GaN layer, so that the electric resistance in the film thickness direction is reduced, so that the electric resistance when carriers are injected from the p-type electrode 311 is reduced.
- the carrier mobility in the layer surface direction is increased by the superlattice structure, and carriers injected from the P-type electrode positioned just above the opening for current injection are used for efficient current injection. It can be concentrated in the opening and used for LD operation. For this reason, the operating voltage applied when obtaining a desired laser beam output can be greatly reduced.
- the p-type cladding layer 309 has a superlattice structure, dislocations generated at the interface between A1N, which becomes the current confinement layer 308, and the superlattice structure layer are laterally bent, and reaction between dislocations occurs. Disappear more. As a result, the crystal quality of the superlattice structure layer is greatly improved.
- the dislocation density force of the p-type cladding layer 309 is relatively low in the region immediately above the current injection opening provided in the current confinement layer 308 which is relatively high in the region directly above the current confinement layer 308. Therefore, in the region immediately above the current confinement layer 308, a high-resistance semiconductor layer is obtained, and a good current blocking effect is obtained, and in the region immediately above the current injection opening, a low-resistance semiconductor layer is obtained, which is favorable. Current injection is realized.
- a GaNZ AlGaN superlattice structure layer is formed on the p-type GaN guide layer 307, and the number of dislocations generated at the interface is originally low.
- the dislocation density of the p-type cladding layer 309 immediately above the region of the opening ing and 10 8 CM_ less than 2.
- the dislocation density of the p-type cladding layer 309 exceeds 10 9 cm 2 .
- dislocation density force 10 8 CM_ than second p-type cladding layer 309 comprising a superlattice structure layer is a low-resistance semiconductor layer, the dislocation density is more than 10 9 cm 2, a high resistance.
- the composition of Al Ga In N having a high A1 composition used for the current confinement layer 3 08 and the film formation conditions, and the growth conditions of the p-type cladding layer 309 including the GaN / AlGaN superlattice structure layer are appropriately selected.
- the p-type cladding layer 309 itself becomes a high-resistance semiconductor layer immediately above the current confinement layer 308, and a good current blocking effect is obtained. At the same time, in the region immediately above the current injection opening, a low-resistance semiconductor layer is formed, and good current injection is realized.
- the p-type electrode 311 can be formed over the entire surface of the element SiO
- the contact width (electrode width) between the p-type contact layer 310 and the p-type electrode 311 is limited by the opening of the insulating layer, and the end of the opening of the insulating layer is symmetrical with respect to the current injection opening. It is preferable to arrange in.
- the low voltage effect becomes remarkable by setting the opening width (electrode width) of the insulating layer to 10 times or more the opening width of the current injection opening.
- the insulating layer has the effect of reducing the parasitic capacitance of the element, and is advantageous in terms of frequency characteristics.
- a part of the current confinement layer 308 on both sides of the stripe-shaped opening which is a current path may be removed.
- an LD with a current confinement layer formed on the entire surface of the device the process of device isolation, wire 'bonding, heat fusion to the heat sink, etc. due to the large strain caused by the difference in lattice constant between the substrate and the current confinement layer The element is destroyed.
- the coverage of the current confinement layer in the chip area (active layer area) the stress inherent in the entire device is reduced, improving long-term reliability and improving resistance to stress from external forces To do.
- bonding stress can be avoided in the current confinement layer by providing a bonding pad in the dummy opening. Damage can be minimized.
- a pair of stripe-shaped current confinement layers provided on both sides of the stripe-shaped opening is preferable. At that time, since it is necessary to suppress current leakage to the outside of the stripe-shaped current confinement layer and the region from which the current confinement layer has been removed, a structure in which the electrode width is limited by forming an insulating layer is selected.
- each stripe current confinement layer and the electrode width it is necessary to select the width of each stripe current confinement layer and the electrode width so that the total width of the width of each stripe current confinement layer and the opening width of the current injection opening is increased. .
- the width of each strip-like current confinement layer is at least 0.5 times the electrode width, more preferably 0. Select at least 7 times.
- the coverage of the current confinement layer in the chip area (active layer area) can be selected in the range of 50% or less and 2.5% or more.
- the current confinement layer 308 undoped A1N, (Al) GaN, or the like is used.
- An n-type impurity such as silicon or oxygen may be doped.
- Mg which is a p-type impurity, diffuses during the buried growth of the p-type cladding layer, increasing the reactive current, but by doping the current confinement layer with n-type impurities, This can be compensated for and the reactive current can be reduced.
- a depletion layer by a pn junction is formed at the interface between the current confinement layer and the p-type cladding layer, more complete current confinement is performed, and, for example, the threshold current of laser oscillation is reduced.
- an undoped GaN layer can be provided on the surface of the current confinement layer 308 facing the p-type cladding layer.
- the undoped GaN layer provided on the surface of the current confinement layer 308 diffuses Mg, which is a P-type impurity, during the buried growth of the p-type cladding layer, and the portion in contact with the p-type cladding layer exhibits p-type conductivity. Converted to GaN.
- the diffusion of the p-type impurity beyond the undoped GaN layer and reaching the current confinement layer 308 is effectively suppressed.
- the thickness of the undoped GaN layer that fulfills the above function may be about 1/10 to 1Z2 with respect to the thickness of the current confinement layer 308.
- the total thickness of the undoped GaN layer and the current confinement layer 308 is selected to be thinner than the thickness of the p-type cladding layer.
- the total thickness of the undoped GaN layer and the current confinement layer 308 is selected to be thinner than the thickness of the p-type cladding layer.
- by providing an undoped GaN layer formed by high-temperature growth in advance on the surface of the current confinement layer 308 using undoped A1N, (Al) GaN, or the like grown at low temperature it is easy to embed the p-type cladding layer. Become.
- insulating materials such as silicon oxide and silicon nitride can also be used as a constituent material of the current confinement layer 308.
- this insulating material is used, a more complete current confinement is possible.
- polycrystalline growth occurs on the current confinement layer 308 made of an insulating material, and the entire surface of the device is formed. A flat surface cannot be obtained.
- the P-type cladding layer grown on the surface of the stripe-shaped opening has a current that is an insulating material force. When the surface of the constriction layer 308 is reached, lateral growth occurs.
- the thickness of the current confinement layer 308 made of an insulating material is preferably selected in the range of 50 nm or more and lOOnm or less.
- a flat portion wider than the current injection opening is obtained by lateral growth of the p-type cladding layer from the stripe opening to the surface of the current confinement layer 308 also having an insulating material force.
- the p-type impurity doping of the p-type cladding layer 309 may be performed on either or both of the AlGaN layer and the GaN layer constituting the superlattice structure.
- a modulation doped superlattice structure in which only the AlGaN layer is doped with Mg is desirable.
- the modulation-doped superlattice structure in which only the AlGaN layer is doped with Mg has the effect of improving the flatness of the buried growth.
- the LD according to this example has the same basic structure as that shown in the first embodiment (FIG. 3). Hereinafter, the manufacturing method will be described.
- n-type GaN (0001) substrate was used as the substrate.
- a MOVPE device is used to fabricate the device structure.
- a mixed gas of hydrogen and nitrogen is used as a carrier gas, and trimethylgallium (TMG), trimethylaluminum (TMA), trimethylindium (TMI), and silane (SiH) as n-type dopants as Ga, Al, and In sources, respectively.
- TMG trimethylgallium
- TMA trimethylaluminum
- TMI trimethylindium
- SiH silane
- Biscyclopentadiene as p-type dopant
- this process is referred to as an “active layer growth process”.
- the temperature of the substrate is increased while NH is supplied to grow the substrate.
- Three-period multiple quantum well consisting of Ga N (Si concentration l X 10 18 cm _3 , thickness 4 nm) barrier layer (
- MQW MQW
- Mg-doped p-type Al Ga N Mg concentration 2 X 10 19 cm_ 3 , thickness 50 nm
- a cap layer 306 made of Mg and a p-type optical confinement layer (guide layer) 307 made of Mg-doped p-type GaN (Mg concentration 2 ⁇ 10 19 cm _3 , thickness 0 .: L m) are sequentially deposited.
- GaN growth is at substrate temperature 10 80 ° C, TMG supply 58 ⁇ mol / min, NH supply 0.36 mol / min, AlGaN growth
- the substrate temperature is 1080 ° C
- the TMA supply is 36 ⁇ mol / min
- the TMG supply is 58 ⁇ mol / min
- the NH supply is 0.3 molZmin.
- the supply rate is 48 ⁇ mol / min for the well layer and 3 ⁇ molZmin for the barrier layer.
- the substrate temperature was subsequently lowered to 400 ° C, and a low-temperature grown A1N layer (thickness 100 ⁇ m, later becoming the current confinement layer 308) was deposited.
- stripe formation process deposit lOOnm of SiO on the A1N layer and apply resist on the surface
- the selective etching solution a solution in which phosphoric acid and sulfuric acid are mixed at a volume ratio of 1: 1 is used.
- A1N layer in the area not covered with SiO mask is 80 ° C
- Stripped openings were obtained by etching for 10 minutes in the above solution held in the above.
- Sarakuko removes the SiO film used as a mask with noferred hydrofluoric acid, and forms an A1N layer.
- a structure having a 2 ⁇ m wide stripe-like opening is obtained.
- the n-type cladding layer 303, the n-type optical confinement layer 304, and the multiple quantum well for the active layer are identical to the n-type cladding layer 303, the n-type optical confinement layer 304, and the multiple quantum well for the active layer
- An LD wafer including an (MQW) layer 305, a cap layer 306, a p-type optical confinement layer (guide layer) 307, a current confinement layer 308, a p-type cladding layer 309, and a p-type contact layer 310 is obtained.
- a p-type electrode 311 and an n-type electrode 312 are formed for this LD wafer. This process is called an “electrode process”.
- Ti 5nm and Al 20nm are vacuum-deposited in this order on the back surface of the n-type GaN substrate 301, and then Ni 10nm and Au 10nm are vacuum-deposited in this order on the p-type contact layer 310.
- the above sample is put into an RTA apparatus and alloyed at 600 ° C. for 30 seconds to form an ohmic contact.
- Au is vacuum-deposited on the T1A1 film on the back side of the substrate and the NiAu film on the front side to form an n-type electrode 312 and a p-type electrode 311.
- the wafer on which the n-type electrode and the p-type electrode are formed is cleaved into a bar shape in a direction perpendicular to the stripe-shaped current injection opening provided in the current confinement layer, and cleaved.
- a resonator perpendicular to the surface is fabricated. TiO tA ⁇ O on the cavity end face
- the bar is cut in the direction to make a laser element as shown in FIG.
- the resonator length is 600 m and the element width is 400 ⁇ m.
- the dislocation density (8 X 10 10 cm “ 2 ) in the p-type cladding layer of the superlattice structure in the region immediately above the current confinement layer was The dislocation density of the p-type cladding layer in the region directly above the stripe-shaped current injection opening was more than 100 times the dislocation density (6 X 10 7 cm_ 2 ).
- the LD chip obtained by the above process was fused on a heat sink in a P-side 'up arrangement, and each electrode was wire-bonded.
- the obtained semiconductor laser was excellent in current injection efficiency, operated at a low voltage, and was not easily damaged by wire bonding or the like.
- Figure 4 shows the schematic structure of the LD according to this example.
- the area where the p-type electrode 311 and the p-GaN contact layer 310 are in contact with each other is limited by the insulating layer 313, and this point is different from the device of Example 1.
- a method for manufacturing this semiconductor laser will be described.
- a ⁇ m-wide stripe-shaped opening is formed immediately above the stripe-shaped current injection opening provided in the current confinement layer. Thereafter, the same “electrode process” as in the first embodiment is obtained, and the p-type electrode 311 and the n-type electrode 312 are formed.
- the wafer obtained by the above process is cleaved in a bar shape in a direction perpendicular to the stripe-shaped current injection opening provided in the current confinement layer, and a resonator perpendicular to the cleavage plane is produced.
- the resonator length is 600 m and the element width is 400 m.
- the dislocation density (10 9 ⁇ : ⁇ ⁇ ⁇ 2) in the p-type cladding layer of the superlattice structure in the region immediately above the current confinement layer was The transition of the p-type cladding layer in the region directly above the stripe-shaped current injection opening It was more than 100 times the unit density (10 5 to 10 7 cm — 2 ).
- the LD chip obtained by the above process was fused on a heat sink in a P-side 'up arrangement, and each electrode was wire-bonded.
- the width of the stripe-shaped opening of the SiO film was changed to 2, 5, 10, 20, 50, 100 ⁇ m.
- the capacitance of the entire laser element measured at a voltage of 4 V applied to the element increases from 15 pF to 30 pF as the width increases.
- the capacitance of the entire laser element measured at a voltage of 4 V applied to the element is 50 pF.
- the surface of the p-type contact layer 310 is covered with a SiO film having a thickness of 5000 angstroms or more having an opening with a width of 20 ⁇ m, and the element area (element width 400 m)
- the width of the contact portion of the p-type electrode with respect to the p-type contact layer 310 is limited to about 10 times the width of the current injection opening provided in the current confinement layer.
- the obtained semiconductor laser had excellent current injection efficiency, low capacity and low voltage operation, and was hardly damaged by wire bonding or the like.
- the schematic structure of the LD according to this example is shown in FIG.
- a part of the current confinement layer 308 is removed in the regions on both sides of the stripe-shaped opening serving as a current path. This is different from the elements of Examples 1 and 2. The manufacturing method will be described below.
- the method described in the “stripe formation step” is performed on both sides of the 2 m-width stripe-shaped openings serving as current paths.
- the structure has a striped A1N layer with m width.
- the area occupied by the current confinement layer 308 composed of two striped A1N layers is about 20%.
- the n-type cladding layer 303, the n-type guide layer 304, the active layer 305 and the cap layer 306, the p-type guide layer 307, the current An LD wafer having a constriction layer 308, a p-type cladding layer 309, and a p-type contact layer 310 is obtained.
- a SiO film with a film thickness of 7000 angstroms was formed on the p-type contact layer 310 as the insulating layer 313 by the CVD method.
- a 20 m wide stripe-shaped opening is formed by photolithography.
- the stripe-shaped opening is formed to be located immediately above the current injection opening provided in the current confinement layer.
- an “electrode process” similar to that of the first embodiment is obtained, and the p-type electrode 311 and the n-type electrode 312 are formed.
- the wafer obtained by the above steps is cleaved in a bar shape in a direction perpendicular to the stripe-shaped current injection opening provided in the current confinement layer, and a resonator perpendicular to the cleavage plane is produced.
- the resonator length is 600 m and the element width is 400 m.
- the dislocation density (10 9 ⁇ : ⁇ ⁇ ⁇ 2) in the p-type cladding layer of the superlattice structure in the region immediately above the current confinement layer was The dislocation density (10 5 to 10 7 cm — 2 ) of the p-type cladding layer in the region immediately above the stripe-shaped current injection opening was 100 times or more.
- the LD chip obtained by the above steps was fused on a heat sink in a P-side 'up arrangement, and each electrode was wire-bonded.
- the region where the current confinement layer of low-temperature growth A1N is removed, provided at both sides of the 2 ⁇ m-wide stripe current injection opening serving as a current path, is the position of the wire bonding. It has been confirmed that the device reliability is greatly improved by providing in the above.
- a flat buried growth of a p-type cladding layer with a superlattice structure is possible over the entire wafer, and a low-voltage operation LD element with element yield and long-term reliability can be stably obtained over the entire wafer. Came out.
- a semiconductor laser is fabricated in the same manner as in Example 3 except that the current confinement layer 308 is composed of an oxygen-doped GaN layer.
- the capacitance of the entire laser device measured at a voltage of 4V applied to the device is 30 pF.
- the capacitance of the entire laser device measured at a voltage of 4 V applied to the device is 20 pF.
- the obtained semiconductor laser was excellent in current injection efficiency, operated at a low capacity and at a low voltage, and was hardly damaged by wire bonding or the like.
- a flat buried growth of a p-type cladding layer having a superlattice structure is possible over the entire wafer, and it is possible to stably obtain a low-voltage operation LD element having a device yield and long-term reliability over the entire wafer. did it [0078] (Comparative Example 1)
- a semiconductor laser was fabricated and evaluated in the same manner as in Example 1 except that a high-temperature grown GaN layer was used as the current confinement layer 308.
- the growth of the high-temperature GaN layer is performed using the conditions for producing a GaN film exhibiting n-type conductivity having a resistivity of 0.5 ⁇ ⁇ cm.
- the substrate temperature was kept at 1080 ° C, and a current confinement layer having GaN force was grown at this temperature.
- the thickness of the current confinement layer is about 50 nm.
- the GaN current confinement layer was selectively dry etched to provide a 2 m wide stripe-shaped opening.
- the sample having the stripe opening obtained as described above is subjected to the steps after the “p-clad regrowth step” to obtain a semiconductor laser.
- the cross-sectional structure of the obtained LD chip was observed with a transmission electron microscope, the dislocation density in the p-type cladding layer of the superlattice structure was almost uniform, and the dislocation density in the upper part of the current confinement layer (10 5 to 10 7 cm_ 2 ) and the dislocation density (10 5 to 10 7 cm_ 2 ) in the upper part of the opening (current injection region) provided in the current confinement layer, it was confirmed that the distribution of the number of dislocations did not occur.
- the obtained LD chip was fused on the heat sink in a P-side 'up arrangement, and each electrode was wire-bonded, and the emission characteristics were examined.
- the heat sink temperature was 25 ° C.
- the semiconductor laser of Example 1 using a low-temperature grown A1N layer as the current confinement layer 308. Then, the slope efficiency is 1.5WZA around the injection current I 60mA.
Abstract
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