Photodiodes operating in the short wavelength range of 1 - 3 µm are essential in many applications with significant societal benefits. Example applications include short wavelength infrared imaging, remote gas detection, and non-invasive optical blood glucose monitoring. Hence, development of SWIR photodetectors with good performance has been an area of active research in the past few decades. This thesis presents experimental investigations on two detector materials suitable for this wavelength range, which are InGaAs/GaAsSb type-II superlattice (lattice matched to InP substrates) and Al0.1In0.9As0.83Sb0.17 (lattice-matched to GaSb substrates).
Two MBE grown InGaAs/GaAsSb type-II superlattice p-i-n wafers contained strained and lattice matched GaAs1-xSbx (x = 0.49 and 0.40) are reported. Optical and electrical characterisations of the devices are performed. Both devices exhibited room temperature cutoff wavelength of ~ 2 µm. Temperature dependence of cut-off wavelength was extracted from photoresponse data between 200 K and room temperature. These results along with literature were then used to validate a nextnano model for temperature dependent cutoff wavelength of T2SL. Good agreement across the temperature range was demonstrated for both lattice matched and strained T2SL after correcting the GaAsSb valance band offset bowing parameter from 0 to -1.06 eV. Nevertheless, these low type-II superlattice photodiodes exhibit relatively low quantum efficiency, leading to an experimental investigation on Al0.1In0.9As0.83Sb0.17, so that the photodiode uses a bulk material for photon absorption.
The work Al0.1In0.9As0.83Sb0.17 was carried out to establish the relationship between the impact ionisation coefficients, since it has been used as the absorber material in Separate-Absorption-Multiplication Avalanche Photodiodes (SAM APD) competitive avalanche material in an APD. The work used homojunction diodes with 2 and 4 µm nominal intrinsic region widths. Dark current, capacitance, and avalanche gain versus reverse bias as functions of temperatures for Al0.1In0.9As0.83Sb0.17 were measured. Using three laser wavelengths to produce three carrier injection profiles, extensive avalanche gain data were obtained at three temperatures. The data show that electron ionisation coefficient, a, is larger than hole ionisation coefficient, b. Hence, when Al0.1In0.9As0.83Sb0.17 is used as the absorber material in SAM APD, the avalanche material used should also have a>b, in order to avoid degradation in the SAM APD excess noise performance.
