A semiconductor laser

Abstract

The present invention relates to the technical field of semiconductor optoelectronic devices, and in particular to a semiconductor laser having a confinement factor enhancement structure; an upper waveguide layer having at least two layers of In composition gradient layers In from top to bottom; x Ga 1‑x N / In y Ga 1‑y N, the lower waveguide layer has at least two layers of In composition gradient layers In from top to bottom z Ga 1‑z N / In a Ga 1‑a N, the active layer is In b Ga 1‑b N / In c Al d Ga 1‑c‑d N, the In components of the upper waveguide layer, the lower waveguide layer and the active layer form an In component gradient: a<x<y≤z<b; the carrier distribution inversion in the active region is improved, so that the stimulated radiation in the active region is fed back multiple times in the upper waveguide layer and the lower waveguide layer to form oscillation; the In component gradient also enhances the exciton binding energy and the oscillator strength of the active layer, enhances the confinement effect of the carriers in the active layer, and reduces the refractive index dispersion of the upper waveguide layer and the lower waveguide layer.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor optoelectronic devices, and in particular to a semiconductor laser. Background Art

[0002] Laser devices are widely used in display, communication, medical treatment, weapons, guidance, ranging, cutting, welding and other fields. There are many types of lasers, and the classification methods are also diverse, mainly including solid, gas, liquid, semiconductor and dye types of lasers; compared with other types of lasers, semiconductor lasers have the advantages of small size, light weight, long life and simple structure. There are big differences between lasers and nitride semiconductor light-emitting diodes. 1) Lasers are generated by stimulated radiation of carriers, with a small half-width of the spectrum and high brightness. The output power of a single laser can be in the W level, while nitride semiconductor light-emitting diodes are spontaneous radiation, and the output power of a single light-emitting diode is in the mW level; 2) The current density of the laser reaches KA / cm2, which is more than 2 orders of magnitude higher than that of nitride light-emitting diodes, resulting in stronger electron leakage, more serious Auger recombination, stronger polarization effect, more serious electron-hole mismatch, and more serious efficiency attenuation Droop effect; 3) Light-emitting diodes The tube spontaneously radiates, without any external influence, and it is incoherent light that transitions from high energy level to low energy level, while the laser is stimulated transition radiation, and the energy of the induced photon should be equal to the difference in energy levels of the electron transition, producing photons and induced photons that are completely coherent light; 4) Different principles: Under the action of external voltage, the light-emitting diode produces radiation recombination and luminescence when electron holes transition to the quantum well or pn junction, while the laser needs the lasing conditions to be met before it can be lased. The carrier inversion distribution in the active area must be met, and the stimulated radiation light oscillates back and forth in the resonant cavity. The propagation in the gain medium amplifies the light, meets the threshold condition so that the gain is greater than the loss, and finally outputs the laser.Nitride semiconductor lasers have the following problems: 1) Large internal lattice mismatch and strain cause strong polarization effect, and the strong QCSE quantum confinement Stark effect limits the improvement of laser electro-lasing gain; 2) High internal defect density and unsatisfactory crystal quality; 3) The activation energy of Mg acceptors in p-type semiconductors is large, the ionization efficiency is low, the hole concentration is much lower than the electron concentration, and the hole mobility is much lower than the electron mobility, resulting in serious asymmetric mismatch between electrons and holes in quantum wells; 4) Electron leakage; 5) Low hole injection efficiency; 6) Carrier delocalization; 7) Strong Auger recombination; 8) High optical waveguide absorption loss; 9) Low quantum well luminescence efficiency; 10) Poor p-type resistance and ohmic contact, etc. The following difficulties exist in the production of traditional nitride semiconductor lasers: 1) The increase of In component in quantum well will produce In component fluctuation and strain, the gain spectrum of laser will become wider, and the peak gain will decrease; 2) The increase of In component in quantum well will deteriorate the thermal stability; 3) In is easy to produce segregation; 4) The step difference of valence band of laser will increase, the hole transport in quantum well will be more difficult, the carrier injection will be uneven, and the gain will be uneven; 5) The refractive index dispersion of laser will decrease with the increase of wavelength, resulting in the decrease of mode gain of laser; 6) After laser lasing, the carrier concentration in active region of multi-quantum well will be saturated, the bipolar conductivity effect will be weakened, the series resistance of laser will increase, resulting in the increase of laser voltage; 7) High dislocation density will reduce the life of laser; 8) Intrinsic carbon impurities in p-type semiconductor will compensate acceptors and destroy p-type, etc. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a semiconductor laser having a confinement factor enhancement structure, which improves the carrier distribution inversion in the active region, so that the stimulated radiation in the active region is fed back multiple times in the upper waveguide layer and the lower waveguide layer to form oscillations; the In component gradient also improves the exciton binding energy and oscillator strength of the active layer, improves the confinement effect of the carriers in the active layer, and reduces the refractive index dispersion of the upper waveguide layer and the lower waveguide layer.

[0004] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0005] A semiconductor laser comprises, from bottom to top, a substrate, an n-type cladding layer, a lower waveguide layer, an active layer, an upper waveguide layer, an electron blocking layer, a p-type cladding layer, and a p-type semiconductor, wherein the semiconductor laser has a confinement factor enhancement structure; the confinement factor enhancement structure is composed of the following structures: the upper waveguide layer has at least two layers of In composition gradient layers In from top to bottom. x Ga 1- x N / In y Ga 1-y N, the lower waveguide layer has at least two layers of In composition gradient layers In from top to bottom z Ga 1-z N / Ina Ga 1-a N, the active layer is In b Ga 1-b N / In c Al d Ga 1-c-d N quantum well structure, where the well layer is In b Ga 1-b N, the barrier layer is In c Al d Ga 1-c-d N, the In components of the upper waveguide layer, the lower waveguide layer and the active layer form an In component gradient: a<x<y≤z<b.

[0006] In the above technical solution, the In composition gradient layer In of the upper waveguide layer x Ga 1-x N / In y Ga 1-y The In ion intensity gradient of the lower waveguide layer is 100>y / x>2 as measured by SIMS secondary ion mass spectrometry; z Ga 1-z N / In a Ga 1-a The In ion intensity gradient measured by SIMS secondary ion mass spectrometry is 100>z / x>2, 1>a / z≥0.

[0007] In the above technical solution, the In composition gradient layer In of the upper waveguide layer x Ga 1-x N / In y Ga 1-y The In ion intensities of N measured by SIMS secondary ion mass spectrometry are 1.0E20-2.0E20 (au) and 2E20-4E20 (au), respectively; the In composition gradient layer In of the lower waveguide layer z Ga 1-z N / In a Ga 1-a The intensities of N and In ions measured by SIMS secondary ion mass spectrometry were 2E20~4E20 (au) and 0~1E16 (au), respectively.

[0008] The In components of the upper waveguide layer, the lower waveguide layer and the active layer form an In component gradient: a<x<y≤z<b, forming a confinement factor enhancement structure, improving the carrier distribution inversion in the active region, making the stimulated radiation in the active region feedback multiple times in the upper waveguide layer and the lower waveguide layer to form oscillation, and reducing the threshold current of the laser by 15%; the In component gradient also improves the exciton binding energy and oscillator strength of the active layer, improves the confinement effect of the carriers in the active layer, reduces the refractive index dispersion of the upper waveguide layer and the lower waveguide layer, improves the confinement factor of the laser element by about 20%, and improves the mode gain by 28.5%.

[0009] In the above technical solution, the upper waveguide layer, active layer and lower waveguide layer all have the same H, O and C concentration gradients, and the H, O and C concentration gradients of the three layers are H concentration>O concentration>C concentration as tested by SIMS secondary ion mass spectrometry.

[0010] In the above technical scheme, the H, O, and C concentration gradients of the electron blocking layer and the p-type cladding layer are different from those of the active layer, the upper waveguide layer, and the lower waveguide layer, and the H concentration tested by SIMS secondary ion mass spectrometry is greater than the C concentration and the O concentration, and the H, O, and C concentrations of the electron blocking layer and the p-type cladding layer tested by SIMS secondary ion mass spectrometry are greater than those of the active layer, the upper waveguide layer, and the lower waveguide layer.

[0011] The semiconductor laser also has a laser internal loss reduction structure, which consists of the following structures: the electron blocking layer and the p-type cladding layer have H, O, and C concentration gradients, and the H, O, and C concentrations of the electron blocking layer and the p-type cladding layer tested by SIMS secondary ion mass spectrometry are greater than the H, O, and C concentrations of the active layer, the upper waveguide layer, and the lower waveguide layer; the laser internal loss reduction structure causes the light field absorption of the p-type cladding layer region to be reduced, the internal loss of the laser element to be reduced, and the equivalent refractive index of the active region to be increased, thereby reducing the internal loss of the laser element by 40%, and when the injection current density is 5kA / cm2, the output power of the laser is increased by 18.5%.

[0012] In the above technical solution, the active layer is a multi-quantum well structure, and the multi-quantum well is a periodic structure, and the period is greater than or equal to 1.

[0013] In the above technical solution, the n-type cladding layer, the lower waveguide layer, the active layer, the upper waveguide layer, the electron blocking layer, the p-type cladding layer, and the p-type semiconductor include GaN, AlGaN, InGaN, AlInGaN, AlN, InN, AlInN, SiC, Ga 2 O 3 , any one or any combination of BN, GaAs, GaP, InP, AlGaAs, AlInGaAs, AlGaInP, InGaAs, AlInAs, AlInP, AlGaP, InGaP.

[0014] In the above technical solution, the substrate includes sapphire, silicon, Ge, SiC, AlN, GaN, GaAs, InP, sapphire / SiO 2 Composite substrate, sapphire / AlN composite substrate, sapphire / SiNx, magnesium aluminum spinel MgAl 2 O 4 、MgO、ZnO、ZrB 2 、LiAlO 2 and LiGaO 2 Any type of composite substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic structural diagram of a semiconductor laser according to an embodiment of the present invention;

[0016] Figure 2 is a SIMS secondary ion mass spectrum of a semiconductor laser according to an embodiment of the present invention;

[0017] Reference numerals: 100: substrate; 101: n-type cladding layer; 102: lower waveguide layer; 103: active layer; 104: upper waveguide layer, 105: electron blocking layer, 106: p-type cladding layer, 107: p-type semiconductor. DETAILED DESCRIPTION

[0018] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0019] like Figure 1 As shown, a semiconductor laser according to an embodiment of the present invention includes, from bottom to top, a substrate 100, an n-type cladding layer 101, a lower waveguide layer 102, an active layer 103, an upper waveguide layer 104, an electron blocking layer 105, a p-type cladding layer 106 and a p-type semiconductor 107.

[0020] The substrate 100 is a substrate on which nitride semiconductor crystals can be epitaxially grown, and is used to support the epitaxial materials of each layer of the semiconductor laser element. A substrate having a high transmittance (for example, the transmittance of the light is above 50%) in the wavelength range of the light emitted by the semiconductor light-emitting element can be selected. For example, the substrate 100 includes but is not limited to sapphire, silicon, Ge, SiC, AlN, GaN, GaAs, InP, sapphire / SiO 2 Composite substrate, sapphire / AlN composite substrate, sapphire / SiNx, magnesium aluminum spinel MgAl 2 O 4 、MgO、ZnO、ZrB 2 、LiAlO 2 and LiGaO2 Any type of composite substrate.

[0021] The n-type cladding layer 101 is made on the substrate 100, and its lattice constant matches the lattice constant of the substrate 100. The so-called lattice constant matching means that the lattice constant of the epitaxial material is consistent with the lattice constant of the substrate, and there is no stress between the two during epitaxial growth. The n-type cladding layer 101 limits the light emitted by the active area, so that the light emitted by the active area propagates along the axial direction of the waveguide. Preferably, the growth thickness of the n-type cladding layer 101 is 0-3000nm.

[0022] The lower waveguide layer 102 is made on the n-type cladding layer 101, and its lattice constant matches the lattice constant of the substrate 100. It serves as a carrier confinement layer for light conduction, improving the electron-hole recombination efficiency, and increasing the operating temperature of the laser element. Preferably, the lower waveguide layer 102 is grown to a thickness of 30-2000nm.

[0023] The active layer 103 is made on the lower waveguide layer 102 and is the light-emitting area of ​​the device. It can be an active area structure that emits light between various semiconductor bands and sub-bands. Preferably, the active layer 103 is a multi-quantum well structure, and the multi-quantum well is a periodic structure with a period greater than or equal to 1.

[0024] The upper waveguide layer 104 is made on the active layer 103, and its lattice constant matches the lattice constant of the substrate 100. As a carrier confinement layer, the carriers are confined in the active layer 103, thereby improving the electron-hole recombination efficiency and the operating temperature of the laser element; preferably, the growth thickness of the upper waveguide layer 104 is 30-2000nm.

[0025] The upper waveguide layer 104 has at least two In composition gradient layers from top to bottom. x Ga 1-x N / In y Ga 1-y N, the lower waveguide layer 102 has at least two In composition gradient layers In from top to bottom z Ga 1-z N / In a Ga 1-a N, active layer 103 is In b Ga 1-b N / In c Al d Ga 1-c-d N quantum well structure, where the well layer is In b Ga 1-b N, the barrier layer is In c Al d Ga 1-c-dN, the In components of the upper waveguide layer 104, the lower waveguide layer 102 and the active layer 103 form an In component gradient: a<x<y≤z<b; this In component gradient enables the semiconductor laser of the present invention to have a confinement factor enhancement structure, thereby forming a confinement factor enhancement structure, improving the carrier distribution inversion in the active region, and making the stimulated radiation in the active region feedback multiple times in the upper waveguide layer and the lower waveguide layer to form oscillation, thereby reducing the threshold current of the laser by 15%; the In component gradient also helps to improve the exciton binding energy and oscillator strength of the active layer, improve the confinement effect of the carriers in the active layer, reduce the refractive index dispersion of the upper waveguide layer and the lower waveguide layer, improve the confinement factor of the laser element by about 20%, and improve the mode gain by about 28.5%.

[0026] As a preferred technical solution of the present invention, the In composition gradient layer In of the upper waveguide layer 104 x Ga 1-x N / In y Ga 1-y The In ion intensity gradient of N is 100>y / x>2; the In composition gradient layer In of the lower waveguide layer 102 z Ga 1-z N / In a Ga 1-a The In ion intensity gradient measured by SIMS secondary ion mass spectrometry is 100>z / x>2, 1>a / z≥0.

[0027] More preferably, if Figure 2 As shown, the In composition gradient layer In of the upper waveguide layer 104 x Ga 1-x N / In y Ga 1-y The In ion intensities of N measured by SIMS secondary ion mass spectrometry are 1.0E20-2.0E20 (au) and 2E20-4E20 (au) respectively; the In composition gradient layer In of the lower waveguide layer 102 is z Ga 1-z N / In a Ga 1-a The intensities of N and In ions measured by SIMS secondary ion mass spectrometry were 2E20~4E20 (au) and 0~1E16 (au), respectively.

[0028] As a preferred technical solution of the present invention, Figure 2 As shown, the upper waveguide layer 104, the active layer 103 and the lower waveguide layer 102 all have H, O, and C concentration gradients, and the H, O, and C concentration gradients of the three layers are all H concentration>O concentration>C concentration.

[0029] The electron blocking layer 105 is made on the upper waveguide layer 104. Since the effective mass of electrons is small and the movement speed is high under the action of the electric field, they can easily escape from the quantum well area of ​​the luminous active layer 103. Setting up the electron blocking layer 105 near the p-side can effectively prevent the escape of electrons. When the semiconductor element is working, electrons are injected into the n-side and holes are injected into the p-side. The electrons and holes meet and recombine in the quantum well area of ​​the active layer 103 to emit light.

[0030] The p-type cladding layer 106 is formed on the electron blocking layer 105 to limit the light emitted by the active layer 103 so that the light emitted by the active layer 103 propagates along the waveguide axis. Preferably, the p-type cladding layer 106 has a growth thickness of 500-4000 nm.

[0031] As a preferred technical solution of the present invention, the H, O, and C concentration gradients of the electron blocking layer 105 and the p-type cladding layer 106 are different from those of the active layer 103, the upper waveguide layer 104, and the lower waveguide layer 102, and the H, O, and C concentrations of the electron blocking layer 105 and the p-type cladding layer 106 are greater than those of the active layer 103, the upper waveguide layer 104, and the lower waveguide layer 102, forming a laser internal loss reduction structure, thereby causing the light field absorption in the p-type cladding layer 106 region to be reduced, the internal loss of the laser element to be reduced, and the equivalent refractive index of the active layer 103 to be increased, thereby reducing the internal loss of the laser element by about 40%, and when the injection current density is 5kA / cm2, the output power of the laser is increased by 18.5%.

[0032] The p-type semiconductor 107 is made on the p-type cladding layer 106. The n-layer cladding layer 101, the lower waveguide layer 102, the active layer 103, the upper waveguide layer 104, the electron blocking layer 105, the p-type cladding layer 106, and the p-type semiconductor 107 are sequentially stacked on the substrate 100, and the stacked semiconductor layers are stacked by organic metal chemical vapor deposition (MOCVD), organic metal vapor phase epitaxy (MOVPE), molecular beam epitaxy (MBE) and hydride vapor phase epitaxy (HVPE) and other methods; the n-layer cladding layer 101, the lower waveguide layer 102, the active layer 103, the upper waveguide layer 104, the electron blocking layer 105, the p-type cladding layer 106 and the p-type semiconductor 107 include GaN, AlGaN, InGaN, AlInGaN, AlN, InN, AlInN, SiC, Ga 2 O 3 , any one or any combination of BN, GaAs, GaP, InP, AlGaAs, AlInGaAs, AlGaInP, InGaAs, AlInAs, AlInP, AlGaP, InGaP.

[0033] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A semiconductor laser, comprising, from bottom to top, a substrate, an n-type cladding layer, a lower waveguide layer, an active layer, an upper waveguide layer, an electron blocking layer, a p-type cladding layer and a p-type semiconductor, characterized in that: The semiconductor laser has a confinement factor enhancement structure; the confinement factor enhancement structure is composed of the following structure: the upper waveguide layer has at least two layers of In composition gradient layers In from top to bottom. x Ga 1-x N / In y Ga 1-y N, the lower waveguide layer has at least two layers of In composition gradient layers In from top to bottom z Ga 1-z N / In a Ga 1- a N, the active layer is In b Ga 1-b N / In c Al d Ga 1-c-d N quantum well structure, where the well layer is In b Ga 1-b N, the barrier layer is In c Al d Ga 1-c-d N, the In components of the upper waveguide layer, the lower waveguide layer and the active layer form an In component gradient: a<x<y≤z<b.

2. A semiconductor laser as claimed in claim 1, characterized in that: The In composition gradient layer In of the upper waveguide layer x Ga 1-x N / In y Ga 1-y The In ion intensity gradient of N is 100>y / x>2; the In composition gradient layer of the lower waveguide layer In z Ga 1- z N / In a Ga 1-a The In ion intensity gradient of N is 100>z / x>2, 1>a / z≥0.

3. A semiconductor laser as claimed in claim 2, characterized in that: The In composition gradient layer In of the upper waveguide layer x Ga 1-x N / In y Ga 1-y The In ion strength of N is 1.0E20~2.0E20a.u. and 2E20~4E20a.u. respectively; the In composition gradient layer In z Ga 1-z N / In a Ga 1-a The In ion strength of N is 2E20~4E20a.u. and 0~1E16a.u. respectively.

4. A semiconductor laser as claimed in claim 1, characterized in that: The In components of the upper waveguide layer, the lower waveguide layer and the active layer form an In component gradient: a<x<y≤z<b, forming a confinement factor enhancement structure, improving the carrier distribution inversion in the active region, making the stimulated radiation in the active region feedback multiple times in the upper waveguide layer and the lower waveguide layer to form oscillation, and the threshold current of the laser is reduced by 15%; the In component gradient also improves the exciton binding energy and oscillator strength of the active layer, improves the confinement effect of the carriers in the active layer, reduces the refractive index dispersion of the upper waveguide layer and the lower waveguide layer, improves the confinement factor of the laser element by about 20%, and improves the mode gain by 28.5%.

5. A semiconductor laser as claimed in claim 1, characterized in that: The semiconductor laser also has a laser internal loss reduction structure, which consists of the following structure: the electron blocking layer and the p-type cladding layer have H, O, and C concentration gradients, and the H, O, and C concentrations of the electron blocking layer and the p-type cladding layer tested by SIMS secondary ion mass spectrometry are greater than the H, O, and C concentrations of the active layer, the upper waveguide layer, and the lower waveguide layer.

6. A semiconductor laser as claimed in claim 5, characterized in that: The upper waveguide layer, the active layer and the lower waveguide layer have the same H, O and C concentration gradients, and the H concentration of the three layers tested by SIMS secondary ion mass spectrometry is greater than the O concentration and greater than the C concentration.

7. A semiconductor laser according to claim 1 or 6, characterized in that: The H, O, and C concentration gradients of the electron blocking layer and the p-type cladding layer are different from those of the active layer, the upper waveguide layer, and the lower waveguide layer. According to the SIMS secondary ion mass spectrometry test, the H concentration of the electron blocking layer and the p-type cladding layer is greater than the C concentration and the O concentration. Moreover, the H, O, and C concentrations of the electron blocking layer and the p-type cladding layer tested by the SIMS secondary ion mass spectrometry are greater than those of the active layer, the upper waveguide layer, and the lower waveguide layer.

8. A semiconductor laser as claimed in claim 1, characterized in that: The active layer is In b Ga 1-b N / In c Al d Ga 1-c-d N, the active layer is a quantum well structure, and the well layer is In b Ga 1-b N, the barrier layer is In c Al d Ga 1-c-d N; the quantum well is a periodic structure, and the period is greater than or equal to 1.

9. A semiconductor laser as claimed in claim 1, characterized in that: The n-type cladding layer, lower waveguide layer, active layer, upper waveguide layer, electron blocking layer, p-type cladding layer, and p-type semiconductor include any one or any combination of GaN, AlGaN, InGaN, AlInGaN, AlN, InN, AlInN, SiC, Ga2O3, BN, GaAs, GaP, InP, AlGaAs, AlInGaAs, AlGaInP, InGaAs, AlInAs, AlInP, AlGaP, and InGaP.

10. A semiconductor laser as claimed in claim 1, characterized in that: The substrate includes any one of sapphire, silicon, Ge, SiC, AlN, GaN, GaAs, InP, sapphire / SiO2 composite substrate, sapphire / AlN composite substrate, sapphire / SiNx, magnesium aluminum spinel MgAl2O4, MgO, ZnO, ZrB2, LiAlO2 and LiGaO2 composite substrate.

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