Physics Chat
Type-II InAs/GaSb Superlattices for Long-Wavelength Infrared Detectors
Speaker: Dominic Kwan (KesariaM)
Date: Friday 25 September 2020
Time: 15:00
Venue: Zoom
The 14 ML InAs/ 7 ML GaSb Type-II Superlattice (T2SL) Long-wavelength infrared (LWIR) detector has gained much interest for their promise of high performances and wavelength tunability. To determine if alternative layer thicknesses offer advantages over the conventional 14/7 SL structure, four InAs/GaSb T2SL reference samples were grown by molecular beam epitaxy. The same growth parameters were then used to grow p-i-n diodes with active regions comprised of the conventional 14/7 SL structure and a novel 12/4 SL structure. Single pixel diodes were then fabricated using a standard photolithography process. Temperature dependent current/voltage measurements indicate that the 12/4 SL structure has a lower diffusion current than conventional SL structure and is thus proposed as a viable alternative for diffusion limited barrier devices.
The high costs and limited size of native GaSb substrates has led researchers to consider cheaper alternatives for T2SLs. Two LWIR T2SLs, with 14/7 and 12/4 structures, were grown by MBE on GaAs substrates. An interfacial misfit array (IMF) was used to prevent threading dislocations from propagating into the active region. Material and device characterisation show similar but reduced structural, optical and electrical properties compared to samples on native GaSb substrates. The I - V data was then fitted to well known dark current equations in order to determine the contributing and dominating dark current mechanisms in each case.
While single pixel devices are informative for researches, linear arrays (LA) and focal plane arrays (FPA) are required for industry applications. These complex devices require advanced fabrication techniques such as a well-controlled dry etch and effective surface passivation. Using inductively coupled plasma (ICP) etching high quality mesas have been formed on InAs, GaSb and InAs/GaSb samples.