Epitaxial structure, preparation method thereof and photoelectric device

Abstract

The invention discloses an epitaxial structure, a preparation method thereof and a photoelectric device. The epitaxial structure sequentially comprises an InP substrate, a linear gradual change buffer layer, an n-level Al < 1-y > InyAs / Al < 1-z > InzAs reverse gradual change type superlattice buffer layer, an m-level Al < 1-c > IncAs / Al < 1-d > IndAs strain superlattice buffer layer, an Al < 1-t > IntAs transition layer, an N-type InhAl < 1-h > As, a Ga < 1-f > InfAs absorption layer and a P-type IneAl < 1-eAs > depletion layer from bottom to top. According to the epitaxial structure, the linear gradual change buffer layer, the n-level reverse gradual change type superlattice buffer layer and the m-level strain superlattice buffer layer are sequentially arranged on the surface of the InP substrate, so that stress release can be effectively realized, the defect density of the high-mismatch InGaAs epitaxial surface is reduced, and efficient controllability of process parameters is realized, so that the dark current of the detector is improved, and the performance of the detector is improved. The output power of the device is improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to an epitaxial structure, its fabrication method, and an optoelectronic device. Background Technology

[0002] InGaAs is an important group III-V optoelectronic material, dominating applications in the short-wave infrared (1–3 μm) range and widely used in fiber optic communication, space remote sensing, environmental monitoring, missile early warning and guidance, and other fields. It is well known that InGaAs epitaxial layers and InP substrates can achieve perfect lattice matching in the 1–1.7 μm wavelength range. However, when the wavelength is greater than 1.7 μm, the In composition exceeds 53%, and InGaAs and the substrate are no longer matched, with the lattice mismatch increasing with wavelength. At this point, the epitaxial growth of high-quality InGaAs materials becomes extremely difficult. For the epitaxial growth of mismatched heterostructures InxGaAs (x>0.53) / InP, a compositionally graded buffer layer (such as InGaAs, InAsP, or InAIAs) is needed to alleviate lattice strain and suppress dislocation climb. To extend the cutoff wavelength to longer wavelengths and fabricate so-called wavelength-extended InGaAs detectors, the In composition needs to be increased to reduce the material's bandgap. For example, to extend the cutoff wavelength from 1.7 μm to 2.4 μm, the In composition x needs to be increased from 0.53 to about 0.8, which will result in a lattice mismatch of about +1.85% between the InGaAs and InP substrates.

[0003] The high defect density generated during the growth of polar materials (epitaxial layers) on nonpolar substrates, coupled with the heteroepitaxial growth of highly lattice-mismatched materials (e.g., InAs and Si with a lattice mismatch rate of 11.6%), leads to poor performance of III-V devices on Si substrates. In the heteroepitaxial growth of highly lattice-mismatched materials, ternary compounds such as AlnAs and GalnAs have been shown to be used as buffer layers. In these compounds, crystallographic defects (such as dislocations) caused by stacking faults can be confined to the lower part of the buffer layer, resulting in a nearly defect-free top layer. However, for applications using discrete devices with longer wavelengths (even longer), especially at low temperatures, the large lattice mismatch, due to trap states caused by defects associated with large lattice mismatches, further accelerates the degradation of detector performance despite the lower energy gap of the material. Therefore, further extending the cutoff wavelength of InGaAs detectors remains a challenge.

[0004] To address these technical issues, a novel low-defect superlattice infrared detector epitaxial structure needs to be designed. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, the first aspect of this invention proposes an epitaxial structure that can effectively improve the lattice mismatch problem of high-mismatch short-wave infrared extended wavelength infrared detectors; reduce the defect density in the InGaAs absorption layer, and improve device performance.

[0006] A second aspect of the present invention also provides a method for preparing an epitaxial structure.

[0007] A third aspect of the present invention also provides an optoelectronic device.

[0008] According to a first aspect of the present invention, the epitaxial structure comprises, from bottom to top, an InP substrate, a linearly graded buffer layer, and an n-level Al layer. 1-y In y As / Al 1-z In z As reverse gradient superlattice buffer layer, m-level Al 1- c In c As / Al 1-d In d As strain superlattice buffer layer, Al 1-t In t As transition layer, N-type Al 1-h In h As layer, Ga 1-f In f As absorption layer and P-type In e Al 1-e As exhaustion layer;

[0009] The content of c is 0.74–0.82; the content of d is 0.78–0.84; the content of t is 0.83–0.90; the content of h is 0.82–0.84; the content of f is 0.82–0.84; the content of e is 0.82–0.84; n≥30; m≥15;

[0010] The material of the linear gradient buffer layer is Al. 1-x In x As, where the content of x gradually changes from 0.52 to 0.66;

[0011] Each superlattice layer of the reverse gradient superlattice buffer layer includes Al layers grown sequentially from bottom to top. 1- y In y As layer and Al 1-z In z As layer; as the order of the superlattice layer increases; the Al 1-y In yThe y content in the As layer gradually decreases from 0.8; Al 1-y In y The thickness of the As layer first increases and then decreases; the Al 1-z In z The z content of the As layer gradually increases from 0.66; Al 1-z In z The thickness of the As layer first decreases and then increases;

[0012] The strain superlattice buffer layer, Al 1-c In c As / Al 1-d In d As is a first-order superlattice, and it is repeatedly grown from bottom to top for m orders.

[0013] The extensional structure according to embodiments of the present invention has at least the following beneficial effects:

[0014] This invention involves sequentially depositing a linearly graded buffer layer, an n-level reverse-graded superlattice buffer layer, and an m-level Al layer on the surface of an InP substrate. 1-c In c As / Al 1-d In d The epitaxial structure of the As strained superlattice buffer layer can effectively achieve stress release, reduce the defect density of high mismatch InGaAs epitaxial surface, and achieve efficient controllability of process parameters, thereby improving the dark current of the detector and increasing the output power of the device.

[0015] Furthermore, the linear gradient buffer layer of the present invention achieves the first step of stress release through the linear gradient of the In component.

[0016] Furthermore, the reverse gradient superlattice buffer layer of the present invention further achieves stress release through the reverse gradient of In composition and growth thickness.

[0017] Furthermore, the Al of the present invention 1-c In c As / Al 1-d In d As strained superlattice buffer layers can further reduce residual stress.

[0018] According to a preferred embodiment of the present invention, as the order of the superlattice layer increases, the Al 1-y In y The y content in the As layer gradually decreases from 0.8 to 0.66.

[0019] According to a preferred embodiment of the present invention, as the order of the superlattice layer increases, the Al 1-z In zThe z content of the As layer gradually increased from 0.66 to 0.8.

[0020] According to a preferred embodiment of the present invention, as the order of the superlattice layer increases, the Al 1-y In y The thickness of the As layer was first increased from 2nm to 25nm and then decreased back to 2nm.

[0021] According to a preferred embodiment of the present invention, as the order of the superlattice layer increases, the Al 1-z In z The thickness of the As layer was first reduced from 48nm to 25nm and then increased back to 48nm.

[0022] According to a preferred embodiment of the present invention, the range of n is 30 to 150.

[0023] According to a preferred embodiment of the present invention, the range of m is 15 to 60.

[0024] According to a preferred embodiment of the present invention, the Al 1-c In c As / Al 1-d In d The As superlattice buffer layer consists of 15–60 Al pairs 1-c In c As / Al 1-d In d As is composed of a two-layer cyclic structure.

[0025] According to a preferred embodiment of the present invention, the Al 1-t In t The thickness of the As transition layer is 300–1500 nm.

[0026] According to a preferred embodiment of the present invention, each pair of Al 1-c In c As / Al 1-d In d In the As superlattice buffer layer, Al 1-c In c The thickness of As is 5–20 nm.

[0027] According to a preferred embodiment of the present invention, each pair of Al 1-c In c As / Al 1-d In d In the As superlattice buffer layer, Al 1-d In d The thickness of As is 5–20 nm.

[0028] A method for preparing an epitaxial structure according to a second aspect of the present invention includes the following steps:

[0029] S1. Epitaxially grow a linear gradient buffer layer on an InP substrate;

[0030] S2. An n-level reverse gradient superlattice buffer layer is grown on the surface of a linear gradient buffer layer.

[0031] S3. Epitaxial growth of m-scale Al on the surface of a superlattice layer. 1-c In c As / Al 1-d In d As strain superlattice buffer layer;

[0032] S4, in Al 1-c In c As / Al 1-d In d Surface epitaxial growth of As strained superlattice buffer layer Al 1-t In t As the transition layer;

[0033] S5, in Al 1-t In t N-type Al is epitaxially grown sequentially on the surface of the As transition layer. 1-h In h As layer, Ga 1-f In f As absorption layer and P-type In e Al 1-e As is the depleted layer.

[0034] According to a preferred embodiment of the present invention, the growth method described herein is a metal-organic chemical vapor deposition (MOCVD) method.

[0035] A third aspect of the present invention provides an optoelectronic device comprising the epitaxial structure described in the first aspect of the present invention.

[0036] According to a preferred embodiment of the present invention, the optoelectronic device includes at least one of an infrared detector, an APD photodetector, and a single-photon detector.

[0037] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0038] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0039] Figure 1 This is a schematic diagram of the extensional structure of Embodiment 1 of the present invention;

[0040] Figure 2 This is an IV curve diagram of an embodiment of the present invention;

[0041] Figure 3 This is the TEM image of Comparative Example 2;

[0042] Figure 4 This is a TEM image of Comparative Example 3. Detailed Implementation

[0043] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0044] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0045] Example 1

[0046] This example provides an epitaxial structure, which, from bottom to top, includes an InP substrate, a linearly graded buffer layer, an n-level inversely graded superlattice buffer layer, and an m-level Al layer. 0.25 In 0.75 As / Al 0.18 In 0.82 As strain superlattice buffer layer, Al 0.16 In 0.84 As transition layer, N-type In 0.18 Al 0.82 As, Ga 0.18 In 0.82 As absorption layer and P-type In 0.18 Al 0.82 As depletion layer; structural schematic diagram of epitaxial structure as shown in Figure Figure 1 As shown.

[0047] The material of the linear gradient buffer layer is Al 1-x In x As, where the content of x gradually changes from 0.52 to 0.66;

[0048] Each superlattice layer consists of Al layers grown sequentially from bottom to top. 1-y In y As layer and Al 1-z In z As layer;

[0049] As the order of the superlattice layer increases; Al 1-y In y The y content in the As layer gradually decreases from 0.8; Al1-y In y The thickness of the As layer first increases and then decreases; Al 1-z In z The z content of the As layer gradually increases from 0.66; Al 1-z In z The thickness of the As layer first decreases and then increases.

[0050] The preparation method is as follows:

[0051] S1. Using InP single crystal material with

[100] crystal orientation as the substrate, a linear gradient buffer layer is grown on the substrate by metal-organic chemical vapor deposition (MOCVD); specifically as follows:

[0052] AlIn with a thickness of approximately 1000 nm was grown. 0.52 As is used as a matching buffer layer to obtain a relatively smooth and glossy surface; subsequently, AlIn 0.52 As a match for the positive gradient change in the composition of the buffer layer material during growth, this material is 0.8 μm AlIn 0.52 ~ 0.66 The As and In components have a progressive relationship of 2%.

[0053] S2. An n-order reverse-gradient superlattice buffer layer is grown on the surface of the linearly graded buffer layer; specifically as follows:

[0054] Al 0.18 In 0.80 As / Al 0.34 In 0.66 As is a pair of superlattices, where AlIn 0.80 As decreases in the opposite direction, AlIn 0.66 As increases in a positive direction, growing 75 superlattice pairs until Al... 0.18 In 0.80 As / Al 0.34 In 0.66 As gradually transitions to Al 0.34 In 0.66 As / Al 0.18 In 0.80 As, complete Al 0.48 In 0.52 As to Al 0.20 In 0.80 As lattice transition.

[0055] S3. Epitaxial growth of Al on the surface of a reverse gradient superlattice buffer layer. 0.25 In 0.75 As / Al 0.18 In 0.82 As a strained superlattice buffer layer; the specific steps are as follows:

[0056] Al 0.25 In 0.75 As / Al 0.18 In 0.82 As is a pair of superlattices, 30 pairs of Al are grown. 0.25 In 0.75 As / Al 0.18 In 0.82 As superlattice buffer layers, each layer is 10nm thick.

[0057] S4, sequentially regrowing 800nm ​​AlIn 0.85 As transition layer, 1000nm n-AlIn 0.82 As, 2μm Ga 0.18 In 0.82 As absorption layer and 600nm p-AlIn 0.82 As is the depleted layer.

[0058] Comparative Example 1

[0059] Comparative Example 1 provides an epitaxial structure with the same structure and preparation method as Example 1, except that it lacks the reverse gradient superlattice buffer layer and Al. 0.25 In 0.75 As / Al 0.18 In 0.82 As strain superlattice buffer layer;

[0060] That is, based on S1, in AlIn 0.52 As the composition of the buffer layer material changes positively with the growth of the matching buffer layer, this material is 3μm AlIn 0.52 ~ 0.82 The As and In compositional progression is 2%. Subsequently, 800 nm AlIn was grown. 0.85 As transition layer, 1000nm n-AlIn 0.82 As, 2μm Ga 0.18 In 0.82 As absorption layer and 600nm p-AlIn 0.82 As is the depleted layer.

[0061] Comparative Example 2

[0062] Comparative Example 2 provides an epitaxial structure with the same structure and preparation method as Example 1, except that it lacks Al. 0.25 In 0.75 As / Al 0.18 In 0.82 As strain superlattice buffer layer.

[0063] That is, based on S2, Al 0.16In 0.82 As / Al 0.34 In 0.66 As is a pair of superlattices, where AlIn 0.82 As decreases in the opposite direction, AlIn 0.66 As increases in a positive direction, growing 100 superlattice pairs until Al... 0.16 In 0.82 As / Al 0.34 In 0.66 As gradually transitions to Al 0.34 In 0.66 As / Al 0.16 In 0.82 As, complete Al 0.48 In 0.52 As to Al 0.16 In 0.82 As lattice transition. Subsequently, 800nm ​​AlIn was grown. 0.85 As transition layer, 1000nm n-AlIn 0.82 As, 2μm Ga 0.18 In 0.82 As absorption layer and 600nm p-AlIn 0.82 As is the depleted layer.

[0064] Comparative Example 3

[0065] Comparative Example 3 provides an epitaxial structure, referring to the literature (Ji L, Lu SL, Zhao YM, et al. Compositionally undulating step-graded InAs y P 1-y Buffer layer growth by metal-organic chemical vapor deposition[J].Journal of Crystal Growth, 2013, 363: 44-48) was prepared.

[0066] Performance testing

[0067] The epitaxial structures of Embodiment 1 and Comparative Examples 1-3 of the present invention were fabricated into detectors and then fabricated using conventional processes. The fabrication steps are as follows:

[0068] A. A dielectric film is grown on a wafer with an epitaxial structure using PECVD. Diffusion holes are prepared by semiconductor processes such as photolithography, etching, and cleaning to remove resist. Then, the wafer is put into an MOCVD machine for Zn doping.

[0069] B. After completing Zn doping, remove the mask layer for Zn diffusion, grow another dielectric film as a surface passivation layer, and then open the P contact layer and N contact layer regions through semiconductor processes such as photolithography, etching, cleaning and resist removal.

[0070] C. P is then grown using methods such as magnetron sputtering;

[0071] D. Finally, IV testing is performed using a B1500 semiconductor test analyzer, followed by calculation using the formula (Jsc = I). d / S)

[0072] The dark current density was obtained. The data for the dark current density are shown in Table 1.

[0073] Table 1

[0074]

[0075]

[0076] As can be seen from Table 1, under the same fabrication process, the dark current density of Comparative Example 2 is reduced compared to Comparative Example 1, by a factor of 2, and the leakage current of the device shows a decreasing trend. This is further supported by the differences in the epitaxial structures of the two examples and their corresponding TEM characterization images. Figure 3 The TEM image is for Comparative Example 1; Figure 4 (TEM image of Comparative Example 2) This illustrates that the defects in the epitaxial structure of Comparative Example 2 are reduced. Similarly, the epitaxial structure of Example 1 is further optimized compared to Comparative Example 2, and the defects are further reduced. Test results show that the dark current density of Example 1 is reduced by 3 times compared to Comparative Example 2, indicating that the optimization of the epitaxial structure is effective and the epitaxial structure of the example is further improved. Under the same test conditions, the dark current density of Example 1 is significantly reduced compared to Comparative Example 3. Compared with the epitaxial structures in the literature, the epitaxial structure of the present invention has superior electrical performance.

[0077] The IV curves of the detectors prepared by the epitaxial mechanisms provided in the embodiments of the present invention and Comparative Examples 1 to 3 are as follows: Figure 2 As shown, the increase in current density with increasing reverse bias voltage gradually decreases, indicating that the embodiments of the present invention have an improvement effect on the defects of the high mismatch structure layer. The flat region of the dark current of the structure layer under high bias voltage is significantly lengthened, indicating that the tunneling leakage current caused by defects is reduced.

[0078] The present invention has been described in detail above with reference to the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. An epitaxial structure, characterized in that, The epitaxial structure, from bottom to top, includes an InP substrate, a linear gradient buffer layer, and an n-level Al layer. 1-y In y As / Al 1-z In z As reverse gradient superlattice buffer layer, m-level Al 1-c In c As / Al 1-d In d As strain superlattice buffer layer, Al 1-t In t As transition layer, N-type Al 1-h In h As layer, Ga 1-f In f As absorption layer and P-type In e Al 1-e As exhaustion layer; The content of c is 0.74–0.82; the content of d is 0.78–0.84; the content of t is 0.83–0.90; the content of h is 0.82–0.84; the content of f is 0.82–0.84; the content of e is 0.82–0.84; n≥30; m≥15; The material of the linear gradient buffer layer is Al. 1-x In x As, where the content of x gradually changes from 0.52 to 0.66; Each superlattice layer of the reverse gradient superlattice buffer layer includes Al layers grown sequentially from bottom to top. 1-y In y As layer and Al 1-z In z As layer; as the order of the superlattice layer increases; the Al 1-y In y The y content in the As layer gradually decreases from 0.8; Al 1-y In y The thickness of the As layer first increases and then decreases; the Al 1-z In z The z content of the As layer gradually increases from 0.66; Al 1- z In z The thickness of the As layer first decreases and then increases; The strain superlattice buffer layer, Al 1-c In c As / Al 1-d In d As is a first-order superlattice, and it is repeatedly grown from bottom to top for m orders.

2. The epitaxial structure according to claim 1, characterized in that, As the order of the superlattice layer increases, the Al 1- y In y The y content in the As layer gradually decreases from 0.8 to 0.

66.

3. The epitaxial structure according to claim 1, characterized in that, As the order of the superlattice layer increases, the Al 1- z In z The z content of the As layer gradually increased from 0.66 to 0.

8.

4. The epitaxial structure according to claim 1, characterized in that, As the order of the superlattice layer increases, the Al 1- y In y The thickness of the As layer was first increased from 2nm to 25nm and then decreased back to 2nm.

5. The epitaxial structure according to claim 1, characterized in that, As the order of the superlattice layer increases, the Al 1- z In z The thickness of the As layer was first reduced from 48nm to 25nm and then increased back to 48nm.

6. The epitaxial structure according to claim 1, characterized in that, The range of n is 30 to 150.

7. The epitaxial structure according to claim 1, characterized in that, The Al 1-c In c As / Al 1-d In d The As superlattice buffer layer consists of 15–60 Al pairs 1-c In c As / Al 1-d In d As is composed of a two-layer cyclic structure.

8. The epitaxial structure according to claim 1, characterized in that, The Al 1-t In t The thickness of the As transition layer is 300–1500 nm.

9. A method for preparing an epitaxial structure as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Epitaxially grow a linear gradient buffer layer on an InP substrate; S2. An n-level reverse gradient superlattice buffer layer is grown on the surface of a linear gradient buffer layer. S3. Epitaxial growth of m-scale Al on the surface of a superlattice layer. 1-c In c As / Al 1-d In d As strain superlattice buffer layer; S4, in Al 1-c In c As / Al 1-d In d Surface epitaxial growth of As strained superlattice buffer layer Al 1-t In t As the transition layer; S5, in Al 1-t In t N-type Al is epitaxially grown sequentially on the surface of the As transition layer. 1-h In h As layer, Ga 1-f In f As absorption layer and P-type In e Al 1-e As is the depleted layer.

10. An optoelectronic device, characterized in that, Includes the epitaxial structure described in any one of claims 1 to 8.

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