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GaSb-based Infrared Detectors on GaAs Substrates using an Interfacial Misfit Array

  • Author(s): Reyner, Charles
  • Advisor(s): Huffaker, Diana L
  • et al.
Abstract

Infrared detectors based on compound semiconductor technology are on the verge of outperforming HgCdTe, the leading infrared material for the past 50 years. The driving force behind this change has been the development of new detector designs based on the 6.1 � lattice constant, which includes GaSb, AlSb, and InAs binary materials. While the epitaxial deposition of these materials on GaSb substrates has enabled high performance devices, key limitations still exist. The lack of a large diameter, semi-insulating substrate; a mature, ohmic n-contact to GaSb; and a low k, large bandgap material for avalanche multiplication are all key weaknesses of this material system that further limit device development.

These challenges can be met by the introduction of a new epitaxial growth mode. The growth mode, an interfacial misfit array (IMF), enables the epitaxial deposition of a high quality, relaxed GaSb epilayer on a GaAs substrate without the creation of residual threading dislocations. The IMF achieves this feat through the creation of a 90� dislocation network at the GaSb/GaAs interface, i.e. a gallium dangling bond every 14 GaAs lattice sites.

In this dissertation, the structural, electrical, and optical characterization of IMF-based material and devices are all described. X-ray diffraction experiments are used to show that the dislocation network is nearly perfectly correlated, i.e. there is a 99% correlation between the location of one Lomer dislocation in the IMF network and its adjacent dislocations. Further evidence is given that the material is over 99.5% relaxed after 250 nm of growth, and continues to relax as the GaSb epilayer becomes thicker. Optical RF measurements of GaSb p-i-n homojunctions on GaAs semi-insulating substrates show that the IMF is capable of passing high frequency signals, and that the background acceptor concentration can be reduced to approximately 2 x 1016 cm-3 using Tellurium compensation doping. C-V profiles of one-sided GaAs junctions indicate that the gallium dangling bonds at the IMF interface do behave as acceptors, but that the interface charge density is 1.8E12 per sq. cm, as opposed to the Lomer dislocation density of 3E12 per sq. cm. And finally, avalanche photodiodes using the IMF interface charge are utilized to create gain in 1.55 um detectors, with both GaAs and AlGaAs multiplication regions. Low ionization coefficient ratios between holes and electrons (k values) of 0.1-0.4 are measured, indicating that the ultimate gain bandwidth product for IMF-based devices is several hundred GHz. Delta-doping is also shown to improve the optical response of the devices, without impacting the breakdown voltage or creating a commensurate increase in dark current. In short, IMF-based materials can meet the next challenges awaiting the 6.1 � material system.

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