Semiconductor epitaxial structure, manufacturing method thereof and semiconductor laser

Abstract

The invention discloses a semiconductor epitaxial structure, a manufacturing method thereof and a semiconductor laser. The semiconductor epitaxial structure comprises a substrate, a buffer layer, a transition layer and an epitaxial layer which are arranged in sequence. The transition layer is a first InGaN material layer (In (y) Ga (1-y) N); the epitaxial layer is a second InGaN material layer (In (x) Ga (1-x) N), the epitaxial layer has a material characteristic that changes periodically along the growth direction of the epitaxial layer, and the characteristic is formed by periodically changing the flow ratio of the first carrier gas to the second carrier gas in the mixed carrier gas in the growth process of the epitaxial layer. By arranging the transition layer and combining a special growth mode of the epitaxial layer, InN phase separation caused by lattice mismatch and thermodynamic instability during growth of the InGaN material with a high In component can be synergistically inhibited, so that the crystal quality and the component uniformity of the material are remarkably improved, and the preparation method is suitable for preparing a high-performance long-wavelength photoelectric device.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically, to a group III nitride semiconductor epitaxial structure, a method for manufacturing the same, and semiconductor optoelectronic devices, particularly semiconductor lasers, incorporating the structure. Background Technology

[0002] Group III nitride semiconductor materials, especially indium gallium nitride (InGaN) alloys, have become key materials for manufacturing blue and green light-emitting diodes (LEDs) and laser diodes (LDs) due to their direct and tunable bandgap, covering the spectral range from near ultraviolet to near infrared. To obtain longer wavelength light output, such as green, yellow, or even red light, it is necessary to grow InGaN epitaxial layers with higher indium (In) content.

[0003] However, a key technical challenge in the epitaxial growth of high-In-content InGaN materials is InN phase separation. This phenomenon stems from the significant lattice mismatch (approximately 11%) between indium nitride (InN) and gallium nitride (GaN) and the thermodynamic immiscibility of the solid phases at typical growth temperatures. When the In content in the InGaN alloy exceeds a certain threshold (e.g., 20%), the system energy tends to decrease through phase separation, leading to the spontaneous decomposition of the alloy into In-rich InN clusters and Ga-rich GaN matrix.

[0004] InN phase separation causes a series of serious problems, hindering the realization of high-performance long-wavelength optoelectronic devices: 1. Deterioration of crystal quality: The formation of InN clusters disrupts the periodicity of the crystal lattice, introducing a large number of crystal defects such as dislocations and stacking faults. These defects, acting as nonradiative recombination centers, severely trap charge carriers, thereby significantly reducing the internal quantum efficiency of the material; 2. Composition inhomogeneity: The drastic fluctuations in the In composition inside the material lead to spatial inhomogeneity of the band structure, which will cause severe broadening of the emission spectrum of the device, making it difficult to accurately control the emission wavelength, and reducing the performance consistency and yield of the device. 3. Surface morphology degradation: Phase separation regions often induce the formation of surface defects such as V-pits. Excessive defect density will affect the growth quality of subsequent epitaxial layers and may lead to device leakage, affecting its reliability.

[0005] Existing technologies have proposed several solutions to suppress InN phase separation, such as controlling the stress state of InGaN quantum wells by growing strain-compensating layers or employing low-temperature growth techniques. However, strain-compensating layers have limited effectiveness in suppressing thermodynamically driven phase separation, especially when pursuing extremely high In content. While low-temperature growth can kinetically limit atomic migration and thus suppress phase separation, it typically sacrifices the crystallinity of the material and introduces other types of defects.

[0006] Therefore, there is an urgent need in this field for a new technical solution that can effectively suppress InN phase separation during the growth of high In composition InGaN materials, thereby obtaining an epitaxial layer with high crystal quality and uniform composition, laying the foundation for the development of high-performance long-wavelength nitride optoelectronic devices. Summary of the Invention

[0007] The present invention aims to solve the technical problem that InN phase separation easily occurs during the growth of high In composition InGaN materials in the prior art, which leads to poor crystal quality of epitaxial layer, uneven composition and low luminous efficiency of device.

[0008] To address the aforementioned technical problems, the first aspect of the present invention provides a semiconductor epitaxial structure, comprising: ... Substrate; A buffer layer disposed on the substrate; A transition layer is disposed on the buffer layer, wherein the transition layer is a first InGaN material layer with the chemical formula In （y） Ga （1-y） N, where 0 < y < 1; And an epitaxial layer disposed on the transition layer, the epitaxial layer being a second InGaN material layer with the chemical formula In （x） Ga （1-x） N, where 0 < x < 1; The epitaxial layer has periodically changing material properties along its growth direction. These periodically changing material properties are formed by periodically changing the flow ratio of the first carrier gas to the second carrier gas in the mixed carrier gas supplied to the growth reaction chamber during the growth process of the epitaxial layer.

[0009] In a preferred embodiment, the indium composition y in the first InGaN material layer and the average indium composition x in the second InGaN material layer satisfy the condition: y > x.

[0010] In a preferred embodiment, the substrate is selected from sapphire substrate, silicon carbide substrate, gallium nitride substrate, or silicon substrate.

[0011] In a preferred embodiment, the thickness of the transition layer is 5 nm to 100 nm, and the indium composition y in the first InGaN material layer is 0.15 to 0.40.

[0012] In a preferred embodiment, the epitaxial layer comprises a multi-quantum-well structure, which includes at least one quantum well sublayer and at least one quantum barrier sublayer grown alternately; the quantum well sublayer is composed of the second InGaN material layer. The quantum barrier sublayer may be a GaN material layer or an InGaN material layer. （z） Ga （1-z） N material layers, where z < x.

[0013] In a preferred embodiment, the periodically changing material properties include an indium composition that varies periodically along the growth direction or a crystal defect density that varies periodically.

[0014] A second aspect of the present invention provides a method for manufacturing the above-described semiconductor epitaxial structure, comprising the following steps: A substrate is provided, and a buffer layer is grown on the substrate; A transition layer serving as the first InGaN material layer is grown on the buffer layer; On the transition layer, an epitaxial layer serving as a second InGaN material layer is grown, wherein the step of growing the epitaxial layer includes periodically modulating the flow ratio of a first carrier gas to a second carrier gas in a mixed carrier gas supplied to the growth reaction chamber during the growth process.

[0015] In a preferred embodiment, the first carrier gas is nitrogen and the second carrier gas is hydrogen; the step of periodically modulating the flow ratio includes periodically switching between a first growth stage with a high hydrogen to nitrogen flow ratio and a second growth stage with a low hydrogen to nitrogen flow ratio.

[0016] In a preferred embodiment, the periodic switching period is 5s to 60s; in the first growth stage, the flow ratio of hydrogen to nitrogen is greater than 0.5; in the second growth stage, the flow ratio of hydrogen to nitrogen is less than 0.2, or the flow rate of hydrogen is zero.

[0017] A third aspect of the present invention provides a semiconductor laser comprising a semiconductor epitaxial structure as described in any of the preceding claims.

[0018] Compared with the prior art, the technical solution provided by the present invention has one or more of the following beneficial effects: 1. Effective Suppression of InN Phase Separation: This invention provides a growth template with a more suitable lattice constant and surface energy for subsequent epitaxial layers by setting a transition layer with a high In content, thus initially suppressing phase separation from a strain perspective. Simultaneously, by employing a dynamic control method of periodically modulating the carrier gas flow ratio during the epitaxial layer growth process, growth kinetics are controlled at the atomic scale, further preventing the nucleation and growth of InN clusters. The synergistic effect of these two methods ensures high material homogeneity even at high In content levels.

[0019] 2. Improved crystal quality and surface morphology: Due to the effective suppression of InN phase separation, the density of crystal defects such as dislocations and stacking faults induced by it is significantly reduced, and the crystal integrity of the epitaxial layer is improved. This is usually manifested as a decrease in the full width at half maximum (FWHM) of the X-ray diffraction rocking curve, a smoother surface, and a reduced root mean square roughness.

[0020] 3. Improved device luminescence performance: Increased crystal quality means fewer non-radiative recombination centers, thereby improving the material's internal quantum efficiency. When this structure is applied to optoelectronic devices such as semiconductor lasers, lower operating thresholds, higher slope efficiency, and higher output power can be achieved.

[0021] Enhanced accuracy and stability of wavelength control: The uniformity of material composition ensures a narrower emission spectrum band, making the emission wavelength of the device more precise and controllable, thereby improving the yield of device manufacturing and the reliability of operation. Attached Figure Description

[0022] none. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. It should be noted that the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0024] Example 1 This embodiment provides a semiconductor epitaxial structure for manufacturing a green semiconductor laser and a method for manufacturing the same. The structure is grown in a metal-organic chemical vapor deposition (MOCVD) apparatus, and its structure, from bottom to top, comprises: Substrate: Sapphire (Al2O3) substrate with c-plane (0001) orientation.

[0025] Buffer layer: On the substrate, a 25 nm thick GaN nucleation layer is first grown at a low temperature of 550°C, followed by growing a 2 μm thick high-temperature GaN buffer layer at 1050°C. This buffer layer is designed to improve the crystal quality of subsequent epitaxial layers.

[0026] n-type semiconductor layer: An n-type cladding layer and an n-type waveguide layer are sequentially grown on the buffer layer. The n-type cladding layer is Si-doped n-type Al. 0.08 Ga 0.92 N-layer, 1.2 μm thick, doping concentration 5 × 10⁻⁶ 18 cm -3 The n-type waveguide layer is a Si-doped n-type GaN layer with a thickness of 100 nm.

[0027] Transition layer: Grown on an n-type waveguide layer. The growth temperature was lowered to 780°C, and trimethylgallium (TMGa), trimethylindium (TMIn), and ammonia (NH3) were introduced as source gases. A 20 nm thick In layer was grown in a mixed carrier gas atmosphere of H2 and N2. （y） Ga （1-y） The N-material layer has an indium composition y set to 0.18. The In composition of this transition layer is higher than the average In composition of the subsequent quantum well.

[0028] Epitaxial layer (active region): In this embodiment, it is a multiple quantum well (MQW) structure, disposed on the transition layer, consisting of 3 periods of In （x） Ga （1-x） It consists of N / GaN quantum well / quantum barrier pairs.

[0029] Quantum well sublayer (second InGaN material layer): Target average In composition x = 0.28, thickness 3 nm. Its growth process employs a periodic modulated carrier gas method. At a growth temperature of 740°C, the flow rates of TMGa and TMIn are kept constant, while the total flow rate of the mixed carrier gas (H2 and N2) is kept constant (e.g., 5000 sccm), but the flow ratio of H2 to N2 is periodically modulated. This modulation process comprises two stages: First growth stage: lasts 10 seconds. The H2 flow rate is set to 1500 sccm and the N2 flow rate to 3500 sccm, at which point the H2 / N2 flow rate ratio is approximately 0.43.

[0030] Second growth stage: lasts 15 seconds. Reduce the H2 flow rate to 500 sccm and increase the N2 flow rate to 4500 sccm. At this point, the H2 / N2 flow rate ratio is approximately 0.11.

[0031] The first and second growth stages are treated as one cycle (25 s), and this cycle is repeated until a 3 nm thick quantum well sublayer is grown.

[0032] Quantum barrier sublayer: Interrupting the TMIn flow and raising the temperature to 850°C to grow a 12nm thick GaN barrier layer.

[0033] p-type semiconductor layer: A p-type electron blocking layer, a p-type waveguide layer, a p-type cladding layer, and a p-type semiconductor layer are sequentially grown on top of the epitaxial layer. + Contact layer. The p-type electron blocking layer is Mg-doped p-type Al. 0.15 Ga 0.85 The N-layer is 20 nm thick. The p-type waveguide layer is a Mg-doped p-type GaN layer with a thickness of 100 nm. The p-type cladding is a Mg-doped p-type Al. 0.08 Ga 0.92 N-layer, 0.6 μm thick. p + The contact layer is a heavily Mg-doped p + A GaN layer with a thickness of 20nm.

[0034] After epitaxial growth is completed, the semiconductor laser chip is finally fabricated through standard semiconductor processes, including annealing, photolithography, etching, and electrode fabrication.

[0035] The epitaxial structure sample prepared in this embodiment was characterized. Its high-resolution X-ray diffraction (HRXRD) rocking curve for the (002) crystal plane showed a full width at half maximum (FWHM) of 280 arcsec, indicating excellent crystal quality. Atomic force microscopy (AFM) analysis revealed a root mean square (RMS) roughness of 0.4 nm, indicating a smooth surface morphology. Room temperature photoluminescence (PL) analysis showed a peak emission value near 525 nm, with a narrow spectral line and high emission intensity. These results demonstrate that the technical solution of this embodiment can effectively suppress InN phase separation and obtain a high-quality InGaN epitaxial layer with high In composition.

[0036] Example 2 The semiconductor epitaxial structure and manufacturing method in this embodiment are basically similar to those in Embodiment 1, with the main difference being: 1. Substrate: A GaN homogeneous substrate is used to obtain a lower initial dislocation density.

[0037] 2. Transition layer: The In component y is set to 0.25, and the thickness is 15nm.

[0038] 3. Epitaxial layer: The target average In composition x of the quantum well sublayer in the MQW structure is 0.32 in order to obtain longer wavelength yellow-green light.

[0039] 4. When growing the quantum well sublayer, the parameter for periodically modulating the carrier gas flow rate ratio is adjusted as follows: First growth stage: lasts 8 seconds, H2 / N2 flow rate ratio is set to 0.5.

[0040] Second growth stage: lasts 12 seconds, with H2 flow completely shut off and only N2 used as carrier gas (i.e., H2 / N2 flow ratio is 0).

[0041] This modulation method increases the difference in growth environment between the two growth stages, which is more favorable for the stable growth of materials with higher In content. The device fabricated in this embodiment achieved stable laser lasing near a wavelength of 545 nm.

[0042] Example 3 The manufacturing method of this embodiment is basically similar to that of Embodiment 1, except that the combination of mixed carrier gases used when growing the epitaxial layer (the second InGaN material layer) is different.

[0043] In this embodiment, the mixed carrier gas consists of nitrogen (N2) and argon (Ar). N2 serves as part of the reactant gas and the carrier gas, while Ar acts as an inert dilution gas. By periodically modulating the N2 to Ar flow ratio, the partial pressure and concentration of reactive species (such as NH3 cracking products) near the growth surface can be altered, thereby affecting the incorporation kinetics and surface migration process of In atoms, thus achieving the purpose of regulating growth and suppressing phase separation.

[0044] This demonstrates that the core idea of ​​this invention, namely, improving the quality of high-In-content InGaN materials by periodically modulating the growth atmosphere, can be achieved through different carrier gas combinations, and is not limited to the H2 / N2 system.

[0045] In summary, this invention provides an effective technical approach to solving the phase separation problem in the growth of high-In-content InGaN materials by designing a composite structure comprising a specific transition layer and an epitaxial layer prepared using a dynamic growth method. This solution has significant application value for promoting the development of long-wavelength nitride semiconductor optoelectronic devices, especially green and even longer-wavelength lasers.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A semiconductor epitaxial structure, characterized in that, Including the following settings in sequence: Substrate; A buffer layer disposed on the substrate; A transition layer is disposed on the buffer layer, wherein the transition layer is a first InGaN material layer with the chemical formula In （y） Ga （1-y） N, where 0 < y < 1; And an epitaxial layer disposed on the transition layer, the epitaxial layer being a second InGaN material layer with the chemical formula In （x） Ga （1-x） N, where 0 < x < 1; The epitaxial layer has periodically changing material properties along its growth direction. These periodically changing material properties are formed by periodically changing the flow ratio of the first carrier gas to the second carrier gas in the mixed carrier gas supplied to the growth reaction chamber during the growth process of the epitaxial layer.

2. The semiconductor epitaxial structure according to claim 1, characterized in that, The indium composition y in the first InGaN material layer and the average indium composition x in the second InGaN material layer satisfy the condition: y > x.

3. The semiconductor epitaxial structure according to claim 1 or 2, characterized in that, The substrate is selected from sapphire substrate, silicon carbide substrate, gallium nitride substrate or silicon substrate.

4. The semiconductor epitaxial structure according to claim 1, characterized in that, The thickness of the transition layer is 5 nm to 100 nm, and the indium composition y in the first InGaN material layer is 0.15 to 0.

40.

5. The semiconductor epitaxial structure according to claim 1, characterized in that, The epitaxial layer comprises a multi-quantum-well structure, which includes at least one quantum well sublayer and at least one quantum barrier sublayer that are grown alternately; the quantum well sublayer is composed of the second InGaN material layer.

6. The semiconductor epitaxial structure according to claim 5, characterized in that, The quantum barrier sublayer is a GaN material layer or an In （z） Ga （1-z） N material layer, wherein In （z） Ga （1-z） In the N material layer, the indium composition z satisfies z < x.

7. The semiconductor epitaxial structure according to claim 1, characterized in that, The periodically changing material properties include periodically changing indium composition or periodically changing crystal defect density along the growth direction.

8. A method for manufacturing a semiconductor epitaxial structure as described in any one of claims 1 to 7, characterized in that, Includes the following steps: A substrate is provided, and a buffer layer is grown on the substrate; A transition layer serving as the first InGaN material layer is grown on the buffer layer; On the transition layer, an epitaxial layer serving as a second InGaN material layer is grown, wherein the step of growing the epitaxial layer includes periodically modulating the flow ratio of a first carrier gas to a second carrier gas in a mixed carrier gas supplied to the growth reaction chamber during the growth process.

9. The manufacturing method according to claim 8, characterized in that, The first carrier gas is nitrogen, and the second carrier gas is hydrogen; the step of periodically modulating the flow ratio includes periodically switching between a first growth stage with a high hydrogen to nitrogen flow ratio and a second growth stage with a low hydrogen to nitrogen flow ratio.

10. The manufacturing method according to claim 9, characterized in that, The periodic switching period is 5s to 60s; in the first growth stage, the flow ratio of hydrogen to nitrogen is greater than 0.5; in the second growth stage, the flow ratio of hydrogen to nitrogen is less than 0.2, or the flow rate of hydrogen is zero.

11. A semiconductor laser, characterized in that, It includes the semiconductor epitaxial structure as described in any one of claims 1 to 7.

12. The semiconductor laser according to claim 11, characterized in that, Also includes: An n-type semiconductor layer disposed between the buffer layer and the transition layer; and a p-type semiconductor layer disposed on the epitaxial layer; The n-type semiconductor layer, the transition layer, the epitaxial layer, and the p-type semiconductor layer together constitute the active region of the semiconductor laser and the adjacent waveguide and cladding structure.