Very long wave infrared photon detection using type-II strained layer superlattice structures composed of InAs and GaSb

In this thesis a thorough literature review is taken of infrared type-II superlattice (T2SL) detectors, specifically in the long wave and very long wave bands of the infrared spectrum. Then a mid-wave infrared T2SL detector grown by MBE is fabricated and characterised. A dark current of 1x10-4A/cm2 at 77K is achieved without any surface treatment or passivation. A responsivity of 0.45A/W and detectivity of 1.3x1010cmHz1/2/W is measured at a peak wavelength of 3.7µm and a cut-off wavelength of 4.5µm, at 77K. Following this the device is then modelled using the Schrödinger-Poisson solver Nextnano 3 (Nn3), this is used to confirm the band-gap of the device. A band-gap of 0.353eV equivalent to a 3.5µm cut-off wavelength is simulated. Then the X-ray diffraction (XRD) graph is simulated and compared to experimental data to see the difference between the theoretical structure and that grown by molecular beam epitaxy (MBE). The XRD shows good agreement with the intended structure, with only a 1.5% discrepancy in lattice period. Then the XRD software is used to simulate a Very long-wave infrared (VLWIR) T2SL device grown on an InAs substrate, to lay the foundations for further research into a VLWIR avalanche photodiode (APD). Several strain balanced structures with various interface layers are reviewed.