Superlattice structure and preparation method thereof
By growing a transition layer between GaAs and GaSb and utilizing the thickness design of the InAs/AlSb layer, through-hole dislocations are interrupted and zero mismatch is achieved, thus solving the quality problem of GaSb epitaxial layers and improving device performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- WUHAN GAOXIN TECH
- Filing Date
- 2025-12-25
- Publication Date
- 2026-04-21
AI Technical Summary
In existing technologies, large lattice mismatch between GaSb and GaAs leads to a large number of dislocations, affecting device performance and making it difficult to achieve high-quality GaSb epitaxial layer growth.
A transition layer is grown between the GaAs structural layer and the GaSb buffer layer, including a first transition structure and a second transition structure. The first transition structure breaks through the penetrating dislocations of the GaAs structural layer, and the second transition structure achieves zero mismatch. The thickness design of the InAs/AlSb layer is used to control stress release and mismatch.
This improved the growth quality of the GaSb buffer layer, reduced the sensitivity to process parameters and thermal stability, and solved the device failure problem caused by mismatch dislocations and through dislocations.
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Figure CN121896731A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor technology, specifically to a superlattice structure and its fabrication method. Background Technology
[0002] Antimonides possess advantages such as a wide bandgap coverage, tunable bandgap shift, and high electron mobility, making them widely used in various high-performance optoelectronic devices, including semiconductor lasers, infrared detectors, solar cells, and transistors. However, due to the free carrier absorption effect, undoped GaSb substrates exhibit strong absorption in specific infrared bands, which can affect device performance, and this free carrier absorption effect is difficult to eliminate. Furthermore, GaSb-based devices are difficult to integrate with readout circuits in monolithic technology. Therefore, lattice-mismatch epitaxy of Sb-based materials on GaAs and Si substrates has attracted considerable attention. However, with the introduction of mismatch, the epitaxial layer is limited to a critical thickness. Beyond this thickness, the material releases strain energy through mismatch dislocations and through-dislocations. Vertically propagating through-dislocations are particularly detrimental to device performance, and excessive carriers can significantly impact device performance, increasing nonradiative recombination.
[0003] In recent years, to overcome the problem of a large number of dislocations caused by the large lattice mismatch (~7.8%) between GaSb and GaAs, various methods have been used to improve the quality of GaSb epitaxial layers, such as interface mismatch arrays, compositional gradients, and low-temperature buffer layers. Interface mismatch arrays introduce an ordered array of dislocations (90° mismatch dislocations) at the GaAs / GaSb interface to confine stress within the first few atomic layers, but the process is complex and difficult to fully reproduce. Low-temperature buffer layers involve growing thin GaSb buffer layers on GaAs substrates at low temperatures. While this method is simple and easy to control, the dislocation density remains high. Compositional gradients involve growing GaAsSb compositionally graded layers on GaAs substrates. Although this method results in a smoother stress release, it is not effective against penetrating dislocations. AlSb transition layers directly interrupt penetrating dislocations through a larger mismatch, reducing the mismatch with the upper material. However, AlSb has poor thermal stability and is itself prone to introducing penetrating dislocations. Summary of the Invention
[0004] The purpose of this invention is to provide a superlattice structure and its preparation method, which can at least solve some of the defects in the prior art.
[0005] To achieve the above objectives, embodiments of the present invention provide the following technical solution: a superlattice structure, comprising a GaAs structure layer, and further comprising a transition layer and a GaSb buffer layer sequentially grown on the GaAs structure layer.
[0006] The transition layer includes at least a first transition structure for breaking through dislocations in the GaAs structure layer and a second transition structure that can be zero-mismatched with the GaSb buffer layer.
[0007] The GaAs structure layer, the first transition structure, the second transition structure, and the GaSb buffer layer are grown sequentially.
[0008] Furthermore, the first transition structure includes at least one first InAs / AlSb layer, and in the first InAs / AlSb layer close to the GaAs structure layer, the thickness of the AlSb layer is 5 to 10 times the thickness of the InAs layer.
[0009] Furthermore, the first transition structure includes multiple layers of first InAs / AlSb layers, each of which grows sequentially along the direction from the GaAs structure layer to the GaSb buffer layer, and the thickness of the AlSb layer in each of the first InAs / AlSb layers gradually decreases along the growth direction, while the thickness of the InAs in each of the first InAs / AlSb layers is equal or gradually increases.
[0010] Furthermore, the second transition structure includes a second InAs / AlSb layer, wherein the thickness of the InAs layer is equal to the thickness of the AlSb layer.
[0011] Furthermore, in the second InAs / AlSb layer, the thickness of the InAs layer and the thickness of the AlSb layer are less than 5 mL.
[0012] This invention provides another technical solution: a method for preparing a superlattice structure, comprising the following steps:
[0013] Growth of GaAs structural layers;
[0014] A first transition structure and a second transition structure are grown sequentially on the GaAs structure layer. The first transition structure is used to break the penetrating dislocations of the GaAs structure, and the second transition structure is made to have zero mismatch with the GaSb buffer layer to be grown.
[0015] Continue growing the GaSb buffer layer on the second transition structure.
[0016] Furthermore, during the growth of the first transition structure and the second transition structure:
[0017] The surface of the GaAs structure layer is wetted in a Sb-rich atmosphere.
[0018] First, an AlSb layer is grown, and then an InAs layer is grown on the AlSb layer. The AlSb layer and the InAs layer constitute one cycle of growth. Then, multiple cycles of growth are repeated to obtain the first InAs / AlSb layer of the first transition structure.
[0019] The second transition structure is grown according to the growth process of the first InAs / AlSb layer to obtain the InAs / AlSb layer of the second transition structure, and the thickness of the InAs layer in the InAs / AlSb layer of the second transition structure is controlled to be equal to the thickness of the AlSb layer.
[0020] Furthermore, during the growth of the first transition structure:
[0021] After the first InAs / AlSb layer is grown, the growth process of the first InAs / AlSb layer is repeated to complete the growth of the remaining InAs / AlSb layers of the first transition structure. During the sequential growth of each InAs / AlSb layer, the thickness of the AlSb layer in each InAs / AlSb layer decreases layer by layer, and the thickness of the InAs layer in each InAs / AlSb layer is equal or increases layer by layer.
[0022] Furthermore, during the growth of the GaAs structure layer:
[0023] First, the GaAs single crystal substrate is pre-degassed and then placed in the growth chamber for thermal deoxidation to obtain the GaAs substrate.
[0024] A GaAs buffer layer is then grown on the thermally deoxidized GaAs substrate.
[0025] Furthermore, after the As beam protection is cooled to a suitable growth temperature for the antimonide, the first transition structure and the second transition structure are then grown.
[0026] Compared with the prior art, the beneficial effects of the present invention are:
[0027] 1. By growing a transition layer between the GaAs structural layer and the GaSb buffer layer, the through dislocations in the GaAs structural layer are first interrupted by the first transition structure to release stress, and then the zero mismatch between the GaAs structural layer and the GaSb buffer layer is achieved by growing a second transition structure on the first transition structure, thereby improving the growth quality of the GaSb buffer layer.
[0028] 2. By controlling the thickness of the InAs and AlSb layers during the growth process, the thickness of the AlSb layer gradually decreases in each of the sequentially grown InAs / AlSb layers. This reduces the sensitivity of the process parameters, results in a smoother stress release, and improves thermal stability. In the last InAs / AlSb layer, the thickness of the InAs layer is equal to the thickness of the AlSb layer, achieving zero mismatch between the InAs / AlSb layer and the subsequently grown GaSb buffer layer. This solves the problem of mismatch dislocations and through dislocations that easily occur during the growth of large-mismatch heteroepitaxial material on GaAs substrates, leading to device failure. Attached Figure Description
[0029] Figure 1 This is a schematic diagram of the materials of each layer of a superlattice structure provided in an embodiment of the present invention;
[0030] Figure 2 for Figure 1 A schematic diagram of the materials in one embodiment;
[0031] Figure 3 This is a schematic diagram of xrd fitting of a superlattice structure provided in an embodiment of the present invention. Detailed Implementation
[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0033] Please see Figure 1This invention provides a superlattice structure including a GaAs structural layer, a transition layer and a GaSb buffer layer grown sequentially on the GaAs structural layer. The transition layer includes at least a first transition structure for breaking through dislocations in the GaAs structural layer and a second transition structure that has zero mismatch with the GaSb buffer layer. The GaAs structural layer, the first transition structure, the second transition structure, and the GaSb buffer layer are grown sequentially. In this embodiment, by growing a transition layer between the GaAs structural layer and the GaSb buffer layer, the first transition structure breaks through dislocations in the GaAs structural layer, releasing stress. Then, the second transition structure grown on the first transition structure achieves zero mismatch between the GaAs structural layer and the GaSb buffer layer, improving the growth quality of the GaSb buffer layer. Specifically, by designing the material of the first transition structure, through-dislocation defects in the GaAs structural layer with large negative mismatch can be broken, releasing stress in the GaAs structural layer and preventing vertical propagation of strain energy. Furthermore, by designing the material of the second transition structure, zero mismatch is achieved between the second transition structure and the GaSb buffer layer, resulting in better growth quality of the subsequently grown GaSb buffer layer.
[0034] Please see Figure 1The first transition structure is refined, comprising at least one first InAs / AlSb layer. When there is only one first InAs / AlSb layer, the thickness of the AlSb layer is designed to be 5 to 10 times the thickness of the InAs layer. This allows for the use of more and larger AlSb layers in the first InAs / AlSb layer to compensate for defects in the GaAs structure layer by employing positive mismatch (e.g., the thickness of the AlSb layer is 5 to 10 times the thickness of the InAs layer), thus avoiding the adverse effects of strain energy. Examples of the choices for the AlSb and InAs layers include: 10 mL of AlSb layer and 2 mL of InAs layer, or 20 mL of AlSb layer and 2 mL of InAs layer. The thickness of the AlSb layer does not exceed 20 mL but is not less than 2 mL, where ML stands for Monolayer, meaning a thin film composed of a single layer of atoms or molecules. Preferably, the second transition structure includes a second InAs / AlSb layer, in which the thickness of the InAs layer is equal to the thickness of the AlSb layer. This equal thickness of the InAs layer in the second InAs / AlSb layer achieves zero mismatch between the InAs / AlSb layer and the subsequently grown GaSb buffer layer, solving the problem of mismatch dislocations and through-dislocations that easily occur during the growth of large-mismatch heteroepitaxial material on a GaAs substrate, leading to device failure. Specifically, the AlSb layer in the second transition structure is 2ML, and correspondingly, the thickness of the InAs layer in the second transition structure is also 2ML. However, in the second InAs / AlSb layer, the thickness of both the InAs layer and the AlSb layer is less than 5ML. When they are equal, the thicknesses of both the InAs layer and the AlSb layer should not be too large, which is beneficial to the stability of the superlattice structure. In the first InAs / AlSb layer of the first transition structure close to the second transition structure, the AlSb layer can be 4ML, 3ML, or even 2ML; this embodiment does not limit this.
[0035] Please see Figure 1 Further refining the first transition structure described above, the first transition structure includes multiple layers of first InAs / AlSb layers. Each of the first InAs / AlSb layers grows sequentially along the direction from the GaAs structure layer to the GaSb buffer layer, and the thickness of the AlSb layer in each of the first InAs / AlSb layers gradually decreases along the growth direction, while the thickness of the InAs in each of the first InAs / AlSb layers is equal or gradually increases. This embodiment is... Figure 1 and Figure 2The embodiments shown include cases where the first InAs / AlSb layer has multiple layers. Using more layers of the first InAs / AlSb layer with gradually decreasing AlSb layer thickness reduces the sensitivity to process parameters, provides a smoother stress release, and improves thermal stability. In this embodiment, the InAs thickness in each layer of the first InAs / AlSb layer can be equal, for example... Figure 2 The InAs thickness shown in the embodiments is 2 mL. In other embodiments, the InAs thickness in each of the first InAs / AlSb layers can gradually increase, but ultimately it needs to be equal to the InAs thickness in the second transition structure, and the maximum should not exceed 5 mL. In embodiments where the InAs thickness in each of the first InAs / AlSb layers gradually increases, the mismatch is reduced more quickly because the InAs thickness gradually increases while the AlSb layer thickness gradually decreases, allowing for faster growth of a high-quality transition layer and contributing to the stability of the superlattice structure.
[0036] Please see Figure 1 Further refining the first and second transition structures, the optimal total number of the second InAs / AlSb layer and each of the first InAs / AlSb layers should not exceed five. Fewer structural modifications make it easier to ensure the growth quality of the transition layers.
[0037] As an optimized embodiment of the present invention, both the first InAs / AlSb layer in the first transition structure and the second InAs / AlSb layer in the second transition structure are grown in multiple cycles. The growth cycle of each first InAs / AlSb layer can be two cycles. For example, an InAs layer is grown first, followed by an AlSb layer, which constitutes one cycle. This process is repeated once more, constituting the second cycle. Due to the large positive mismatch in each first InAs / AlSb layer, the growth cycle is designed to be less than or equal to 5, i.e., a, b, c, and d are all greater than or equal to 2 and less than or equal to 5. There is no upper limit to the growth cycle of the second InAs / AlSb layer because the second InAs / AlSb layer and the GaSb buffer have near-zero mismatch. Therefore, more growth cycles result in a thicker layer, which facilitates the masking of defects in the underlying layers and is beneficial for the growth of the upper GaSb buffer. For example, the thickness of the second InAs / AlSb layer can be designed to be 500 nm.
[0038] Please see Figure 1This invention also provides a method for preparing a superlattice structure, comprising the following steps: S1, growing a GaAs structure layer; S2, sequentially growing a first transition structure and a second transition structure on the GaAs structure layer, using the first transition structure to break through dislocations in the GaAs structure, and ensuring zero mismatch between the second transition structure and the GaSb buffer layer to be grown; S3, continuing to grow the GaSb buffer layer on the second transition structure. This preparation method is used to prepare the aforementioned superlattice structure. As in the above superlattice structure embodiment, by growing a first transition structure and a second transition structure between the GaAs structure layer and the GaSb buffer layer, the first transition structure first breaks through dislocations in the GaAs structure layer to release stress, and then the second transition structure grown on the first transition structure achieves zero mismatch between the GaAs structure layer and the GaSb buffer layer, thereby improving the growth quality of the GaSb buffer layer.
[0039] Please see Figure 1 In step S2, the growth of the first transition structure and the second transition structure specifically involves: S20, adjusting the opening of the As source furnace and controlling the pressure value of the As beam, adjusting the opening of the Sb source furnace and controlling the pressure value of the Sb beam, closing the As source furnace, and opening the Sb source furnace to wet the surface of the GaAs structure layer in a Sb-rich atmosphere; S21, opening the Al source furnace and the Sb source furnace, growing an AlSb layer, closing the Al source furnace and the Sb source furnace, pausing for time t1, pre-adjusting the opening of the As source furnace, and opening the In source furnace and the As source furnace, then growing an InAs layer on the AlSb layer. This AlSb layer and the InAs layer constitute one cycle of growth. Closing the In source furnace and the As source furnace, closing the As valve, pausing for time t2, and then repeating multiple cycles of growth to obtain the first InAs / AlSb layer of the first transition structure; S22, growing the second transition structure according to the growth process of the first InAs / AlSb layer to obtain the InAs / AlSb layer of the second transition structure. The AlSb layer is included, and the thickness of the InAs layer in the second transition structure is controlled to be equal to the thickness of the AlSb layer. In this embodiment, the growth methods of the first InAs / AlSb layer in the first transition structure and the second InAs / AlSb layer in the second transition structure are the same, and the control of the number of lattice layers, or the control of the mismatch ratio, can be controlled by the opening degree and pause time of the Al source furnace and the Sb source furnace. As in the above superlattice structure embodiment, during the growth process, by controlling the thickness of the InAs layer and the thickness of the AlSb layer, such as controlling the mismatch between the two to be large, the penetrating dislocations of the GaAs structure layer are interrupted, and the stress is released. Then, by controlling the mismatch between the two to be zero, the growth quality of the GaSb buffer layer can be improved.
[0040] Please see Figure 1 During the growth of the first transition structure: after the first InAs / AlSb layer is grown, the growth process of the first InAs / AlSb layer in step S21 is repeated to complete the growth of the remaining multiple InAs / AlSb layers of the first transition structure. During the sequential growth of each InAs / AlSb layer, the thickness of the AlSb layer in each InAs / AlSb layer decreases layer by layer, and the thickness of the InAs layer in each InAs / AlSb layer is equal or increases layer by layer. In this embodiment, by controlling the thickness of the AlSb layer in each first InAs / AlSb layer of the first transition structure to gradually decrease (along the growth direction from the GaAs substrate to the GaSb buffer layer), the parameter sensitivity of the process can be reduced, stress release can be smoother, and thermal stability can be improved. The thickness of InAs in each first InAs / AlSb layer can be equal, for example... Figure 2 The InAs thickness shown in the embodiments is 2 mL. In other embodiments, the InAs thickness in each of the first InAs / AlSb layers can gradually increase, but ultimately it needs to be equal to the InAs thickness in the second transition structure, and the maximum should not exceed 5 mL. In embodiments where the InAs thickness in each of the first InAs / AlSb layers gradually increases, the mismatch is reduced more quickly because the InAs thickness gradually increases while the AlSb layer thickness gradually decreases, allowing for faster growth of a high-quality transition layer and contributing to the stability of the superlattice structure.
[0041] Please see Figure 1 The GaAs structure layer is grown as follows: First, the GaAs single-crystal substrate is pre-degassed and then placed in a growth chamber for thermal deoxidation to obtain the GaAs substrate; then, a GaAs buffer layer is grown on the thermally deoxidized GaAs substrate. In this embodiment, the GaAs structure layer comprises two parts: a GaAs substrate and a GaAs buffer layer, with the aforementioned transition layer grown on the GaAs buffer layer. During growth, the GaAs single-crystal substrate is first pre-degassed and then placed in a growth chamber for thermal deoxidation to obtain the GaAs substrate, and then the GaAs buffer layer is grown on the thermally deoxidized GaAs substrate. When subsequently growing the transition layer, the temperature is first lowered to a suitable growth temperature for antimonide under As beam protection before growing the transition layer. After the transition layer growth is complete, a GaSb buffer layer is grown under Sb beam protection.
[0042] The following are specific examples:
[0043] Figure 2 One specific implementation is shown, in which the superlattice structure is fitted with xrd as follows: Figure 3As shown in the figure, it can be seen that the final layer of the InAs / AlSb transition layer can be achieved with zero mismatch between the subsequent GaSb epitaxial layer.
[0044] Figure 2 The specific production method is as follows:
[0045] (1) Place the GaAs single crystal substrate in the buffer chamber for pre-degassing. The pre-degassing temperature of the GaAs single crystal substrate is 400℃ and the degassing time is 30min. After the pre-degassing is completed, place it in the growth chamber and perform thermal deoxidation under the protection of the As beam. The As beam is about 1E-5Torr, the thermal deoxidation temperature is 770℃, and the thermal deoxidation time is 20min.
[0046] (2) Grow a GaAs buffer layer at a growth temperature of 750℃. The growth rate of Ga is about 0.5ML / s and the As beam current is about 1E-5Torr.
[0047] (3) The substrate heater is cooled to 545°C. The As source furnace valve is adjusted to 10%, and the As beam current is about 1E-6 Torr. The Sb source furnace valve is adjusted to 40%, and the Sb beam current is about 8E-7 Torr. The As source furnace shutter is closed and the Sb source furnace shutter is opened, so that the surface of the GaAs buffer layer is immersed in the Sb-rich atmosphere for 1 min.
[0048] (4) Open the Al and Sb source furnace shutters. After the AlSb layer growth is completed, close the Al and Sb source furnace shutters, pause for 2 seconds, pre-open the As valve to 10%, then open the In and As source furnace shutters. After the InAs layer growth is completed, close the In and As source furnace shutters, close the As valve, pause for 2 seconds, and grow two cycles of 2ML InAs / 10ML AlSb layers according to the above growth method.
[0049] (5) Continue to grow according to the above growth method. Figure 2 The structure shown keeps the InAs layer thickness constant while gradually decreasing the AlSb layer thickness until the thickness of the fifth InAs layer is equal to the thickness of the AlSb layer, achieving near-zero mismatch with the subsequently grown GaSb layer.
[0050] (6) Under Sb beam protection, the substrate heater is heated to 660°C. After the temperature stabilizes for 2 minutes, GaSb buffer layer is grown, where the Ga growth rate is about 0.5ML / s and the Sb beam current is about 4E-6Torr.
[0051] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A superlattice structure comprising a GaAs structure layer, characterized in that: It also includes a transition layer and a GaSb buffer layer grown sequentially on the GaAs structure layer. The transition layer includes at least a first transition structure for breaking through dislocations in the GaAs structure layer and a second transition structure that can be zero-mismatched with the GaSb buffer layer. The GaAs structure layer, the first transition structure, the second transition structure, and the GaSb buffer layer are grown sequentially.
2. The superlattice structure as described in claim 1, characterized in that: The first transition structure includes at least one first InAs / AlSb layer, and in the first InAs / AlSb layer close to the GaAs structure layer, the thickness of the AlSb layer is 5 to 10 times the thickness of the InAs layer.
3. The superlattice structure as described in claim 2, characterized in that: The first transition structure includes multiple layers of first InAs / AlSb layers. Each first InAs / AlSb layer grows sequentially along the direction from the GaAs structure layer to the GaSb buffer layer. Along the growth direction, the thickness of the AlSb layer in each first InAs / AlSb layer gradually decreases, and the thickness of the InAs in each first InAs / AlSb layer is equal or gradually increases.
4. The superlattice structure as described in claim 1, characterized in that: The second transition structure includes a second InAs / AlSb layer, wherein the thickness of the InAs layer is equal to the thickness of the AlSb layer.
5. The superlattice structure as described in claim 4, characterized in that: In the second InAs / AlSb layer, the thickness of the InAs layer and the thickness of the AlSb layer are less than 5 mL.
6. A method for preparing a superlattice structure, characterized in that, Includes the following steps: Growth of GaAs structural layers; A first transition structure and a second transition structure are grown sequentially on the GaAs structure layer. The first transition structure is used to break the penetrating dislocations of the GaAs structure, and the second transition structure is made to have zero mismatch with the GaSb buffer layer to be grown. Continue growing the GaSb buffer layer on the second transition structure.
7. The method for preparing the superlattice structure as described in claim 6, characterized in that, When growing the first transition structure and the second transition structure: The surface of the GaAs structure layer is wetted in a Sb-rich atmosphere. First, an AlSb layer is grown, and then an InAs layer is grown on the AlSb layer. The AlSb layer and the InAs layer constitute one cycle of growth. Then, multiple cycles of growth are repeated to obtain the first InAs / AlSb layer of the first transition structure. The second transition structure is grown according to the growth process of the first InAs / AlSb layer to obtain the InAs / AlSb layer of the second transition structure, and the thickness of the InAs layer in the InAs / AlSb layer of the second transition structure is controlled to be equal to the thickness of the AlSb layer.
8. The method for preparing the superlattice structure as described in claim 7, characterized in that, When growing the first transition structure: After the first InAs / AlSb layer is grown, the growth process of the first InAs / AlSb layer is repeated to complete the growth of the remaining InAs / AlSb layers of the first transition structure. During the sequential growth of each InAs / AlSb layer, the thickness of the AlSb layer in each InAs / AlSb layer decreases layer by layer, and the thickness of the InAs layer in each InAs / AlSb layer is equal or increases layer by layer.
9. The method for preparing the superlattice structure as described in claim 6, characterized in that: During the growth of the GaAs structural layer: First, the GaAs single crystal substrate is pre-degassed and then placed in the growth chamber for thermal deoxidation to obtain the GaAs substrate. A GaAs buffer layer is then grown on the thermally deoxidized GaAs substrate.
10. The method for preparing the superlattice structure as described in claim 6, characterized in that: After the As beam protection is cooled to a suitable growth temperature for the antimonide, the first transition structure and the second transition structure are then grown.