Mid-wavelength infrared type-II InAs/GaSb superlattice for photodetectors

Abstract

Type-II superlattices (T2SLs) have emerged as a promising technology for infrared detectors compared to the state-of-art mercury cadmium telluride (MCT). T2SLs have shown great potential for mid-wavelength infrared (MWIR) detectors but have yet to attain their theoretically predicted performance. Simulation, fabrication, and characterisation were utilised in this research project to improve the performance levels of MWIR T2SL detectors. Using the molecular beam epitaxy (MBE) reactor, different interfacial growth schemes were used to accommodate internal strain caused by the lattice mismatches in T2SL. The project involves band heterostructure simulations, growth schemes, structural and optical characterisations, and electrical characterisation of fabricated T2SL p-i-n diode. Reference T2SL samples were evaluated by X-ray diffraction (X-RD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). An 8-band k·p approach for band heterostructure simulation explains PL experimental findings. Photoluminescence (PL) measurements probe the band structure and bandgap energy information. T2SL p-i-n diodes fabrication process was optimised using standard photolithography. The diode electrical performance of the T2SLs was examined by current-voltage (I-V) measurements using a cryogenic probe station. Investigation of structural and optical properties of the grown T2SL samples with interfacial growth schemes, namely incorporating an InSb compensation interface (IF) layer, was carried out to improve the material quality. AFM and TEM measurements revealed structural degradation due to the additional strain and lattice mismatch introduced by the InSb IF layers. However, including the InSb IF layer has improved the optical property of the T2SL. Band heterostructure simulation was performed to understand the possibility of atomic intermixing and segregation at the T2SL interfaces. Fabrication processes of T2SL single-pixel diodes were performed by wet etch, dry etch, and a combination of both approaches. The I-V characteristics revealed that the current density of the wet-etched devices is improved by approximately four orders of magnitude at low temperatures in comparison with the dry-etched devices, but they are comparable at high operating temperatures (HOT). Lastly, developments of wet etching processes were investigated using inorganic solutions, such as hydrochloric and phosphoric acids and organic solutions, including citric acid