InAsSb/InAs Strain Balanced Superlattices for Photodetector Applications

Lately, significant research efforts have been directed towards finding III-V alternatives for HgCdTe infrared detectors for optical gas sensing as well as night and machine vision applications. Despite the advantages of HgCdTe, including a tunable bandgap between 1-- 30 im and a high optical absorption coefficient, difficulties in producing uniform material, which are limiting the size of detector arrays and leading to low yield, combined with challenging epitaxial growth and device processing keeps the technology expensive. Recently InAs/Ga(In)Sb type II short period superlattice detectors with cutoff wavelengths between 3 and 30 im have been reported. However, these devices all rely on molecular beam epitaxy for the epitaxial growth, as InAs/(In)GaSb short period superlattices of high quality are extremely challenging to realize by organometallic vapour phase epitaxy (OMVPE). OMVPE growth is desirable since it is very suitable for high volume production, which would lead to a significant cost reduction. Thus we have proposed an InAsSb/InAs strain balanced superlattice detector design grown on GaSb, which is more suitable for OMVPE growth. In this thesis, structural and photoluminescence measurements of InAsSb/InAs superlattices are presented for Sb compositions between 4% and 27%. The layer structures were simulated with a state of the art electronic structure calculator based on a self consistent Poisson and Schroedinger equation solver that includes strain and band-offsets. The calculated transition energies were compared with the measured data. For the first time, the theoretically predicted type IIb alignment, where the InAs conduction band is below the InAsSb conduction band, was confirmed experimentally. The parameters obtained from the simulations were then used to predict the type II transition energies of InAsSb/InAs strain balanced superlattice absorber structures at 77 K for different compositions and periods. The optical matrix element was calculated and compared with that of InAs/(In)GaSb superlattices. The InAsSb/InAs structures can be designed with optical matrix elements that are higher or equal to those of the more well established InAs/Ga(In)Sb superlattices. Finally, initial optical response data of an unoptimized strain balanced InAs0.79Sb0.21/InAs detector is shown. Its cutoff wavelength of 8.5 im (0.15 eV) is in good agreement with the predicted type II transition energy.