Electrical and Computer Engineering ETDs


Brianna Klein

Publication Date



InAs/GaSb type-II strained layer superlattices are a material used for infrared detection. By adjusting the thickness of the InAs and GaSb layers, the material bandgap can be tuned to absorb photons from 3-30 um. Compared to competing materials such as HgCdTe and InSb, InAs/GaSb superlattices are more mechanically robust, have reduced tunneling currents, and can use strain to suppress Auger recombination. In spite of these advantages, this material still faces several challenges, including low minority carrier lifetime, resulting from trap levels that cause Schockley-Read-Hall recombination. These low lifetimes lead to reduced signal-to-noise ratio and higher dark current. Therefore, increasing the lifetime is important for improving this material\'s performance. However, to increase the carrier lifetimes, the origin of the traps must first be understood. In this work, several key suspect causes of the "killer" defect were evaluated. A commonly explored suspect in literature, the interfaces, was studied using time-resolved photoluminescence for three different samples. This characterization method was also used to determine if the doping atom and its layer placement significantly impacted the minority carrier lifetime. There is a substantial amount of evidence that the presence of gallium, or the GaSb layer itself harbors the defect. Thus, the rest of the study focused on aspects of GaSb. Layer intermixing of the In and As atoms into the GaSb layer was studied by intentionally incorporating In and As in bulk GaSb and using photocapacitance characterization to observe any possible defect level formation. In addition, trap level formation for different GaSb growth temperatures was also explored with this characterization technique. Finally, in an attempt to reduce trap densities, GaSb was grown with an increased level of Sb monomers rather than dimers. This material was characterized using dark current density measurements and photoluminescence.'


minority carrier lifetime, superlattice, IR detector, defect

Document Type




Degree Name

Electrical Engineering

Level of Degree


Department Name

Electrical and Computer Engineering

First Committee Member (Chair)

Malloy, Kevin

Second Committee Member

Bandara, Sumith

Third Committee Member

Balakrishnan, Ganesh