In this work, we report a separate absorption and multiplication avalanche photodiode (SAM-APD) with 100% cut-off wavelength of ~2.1 μm at 300 K grown by molecular beam epitaxy. The electron-dominated avalanche mechanism multiplication region was designed as a multi-quantum well structure consisting of AlAsSb/GaSb H-structure superlattice and Al0.3In0.7AsSb digital alloy. At room temperature, the device exhibits a maximum multiplication gain of 79 under -13.3 bias voltage.
Sb segregation is the main contributor to the interfacial asymmetry of the InAs/GaSb superlattices. We reconstructed and quantified the Sb segregation profile in the InAs/Ga(In)Sb superlattice by a one-dimensional model using the postprocessing technique on cross-sectional STM images. The model shows a totally different profile between InAs-on-Ga(In)Sb interface and Ga(In)Sb-on-InAs interface. The asymmetric compositional profile is then added to the 8-band k.p model to investigate its effects on the band structures of the superlattice. With the Sb segregation, the effective band gap of the InAs/GaSb superlattice shifts towards a shorter wavelength. We hope that our work would provide a way to accurately predict the band structures of the InAs/GaSb superlattices by considering the nonideal interfaces.
The band structures of the InAs/GaSb type-Ⅱ superlattice are investigated using the 8-band k.p method. The finite difference method (FDE) is used for solving the Schrödinger equation. It is found that a small variation in the valence band offset (VBO, one of the input parameters) could cause a great change in cut-off wavelength, especially at the long-wavelength range. We also developed a GUI application based on this method. Users could quickly get band structure details, such as bandgap energy, miniband energy, and wavefunctions with this GUI. The program and its code are available at https://github.com/STONEDIY/K.p-Mehtod-for-InAs-GaSb-Superlattice-Band-Structure-Calculation.
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