Defect studies in MBE grown GaSbBi layers

Paper i proceeding, 2013

Gallium antimonide is an interesting material both from a material and a device point of view. The direct, narrow band gap and high electron mobility makes the compound semiconductor a suitable candidate for high speed electronics and optoelectric devices. It can also be used as a substrate material for other ternary or quaternary III–V compounds whose band gaps cover a wide spectral range from 0.8 to 4.3 􀈝m. [1] Incorporating Bi into GaSb has shown to have several advantages compared to, for example, GaNSb. Not only is the band gap reduced [2], but the width of the gap depends very weakly on temperature [3] and the electron mobility is higher than that of GaNSb [4]. The spin-orbit splitting is also larger than the actual band gap which could be used for suppressing Auger-recombinations [5]. Using positron annihilation spectroscopy (PAS) in Doppler broadening mode, we have studied samples of GaSbBi epitaxial layers on GaSb substrates. The PAS technique is based on the interaction between positrons and electrons in solids and can be used for e.g. vacancy defect characterization in thin layers. The studied samples were MBE-grown and the main varied growth parameter was temperature, which lead to different Bi concentrations. The Bi concentrations were 0 - 0.7 %, the epitaxial layer thickness was 200 nm. The substrate was Te-doped (n-type) GaSb. From the measured results, differences between the samples grown under different conditions can be clearly observed. A short diffusion length for the positrons is observed in all of the epitaxial layers, which indicates an increase in positron trapping defects in the layers, compared to the substrate. Furthermore, the Doppler broadening annihilation parameters in the epitaxial layers also seem to depend on the growth temperature and hence, also on the Bi concentration. In order to be able to distinguish the influence of the Bi concentration from the influence of vacancy defects on the Doppler broadening parameters, more accurate measurements need to be conducted. We hope to achieve a better understanding of the positron trapping defect in the epitaxial layers by using coincidence Doppler broadening.