Robin Nicholas

Abstract:

Detectors operating in the 2-3 μm range based on InxGa1-xSb for environmental sensing are investigated. The same detectors which require a low leakage current reverse biased diode are studied for this p-n junction and Schottky barrier diode structures. The p-n hetero-junction between an n-GaAs substrate and the p-GaSb active region showed very good rectification. Despite the large lattice mismatch of -7.8%, there is less than 10 μA dark current up to 4V reverse bias. Increasing the barrier height to p-GaSb from 0.22eV to 0.7eV with use of a thin layer of GaAs have been quite successful but the result was not repeatable, unlike those for the GaSb/GaAs p-n junction.

Abstract:

InAs/GaSb strained layer superlattices (SLSs) have been grown by metalorganic vapour phase epitaxy (MOVPE) at atmospheric pressure. Whilst long period SLSs have been successfully grown by this technique, the growth of short period structures is adversely affected by step-bunching. By growing the SLSs faster and cooler, good periodicity was achieved as measured by Raman spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) in SLSs with bilayer (GaSb + InAs) thicknesses as thin as 50 Angstrom. We have also detected the InSb-like and GaAs-like interface modes from room temperature Raman measurements for the first time in MOVPE grown samples. The most promising samples have been assessed by FIR photoconductivity at 4.2 K and show bandgaps (dependent on the bilayer thickness) between 5 and 20 mu m.