Metastability of deep level defects in gallium-arsenide

John Calvin Parker, Purdue University

Abstract

Spectroscopic and transport measurements on a variety of semi-insulating and n-type GaAs single crystals were used to study the metastable nature of deep level defects in GaAs material. Experiments focusing on transitions to and from these metastable state defects have been studied under various conditions in an effort to gain better comprehension of the defect structure. The metastable defects are responsible for a host of quenching and persistence phenomena which can be long lived when the samples are maintained at low temperatures. Most of our studies have been on the EL2 defect which is a technologically important defect because of the role it plays in the production of semi-insulating GaAs. The identification of EL2 has eluded researchers for years due to the defects ability to undergo a transition to a metastable state where it becomes virtually inaccessible to any experimental probes. In this work we present our results from a series of experiments which probe the defects as they go to and from their mysterious metastable state. We have been able to determine some of the properties the defects have in their normal and metastable states. Some of these properties include the defect charge state as it undergoes the metastable transition, the influence of neighboring impurities which present a modified mechanism of recovery from the metastable state, and a better understanding of how the defects undergo the metastable transition. These conditions should help further the EL2's eventual identification. In the course of our studies on the EL2 defect we have discovered and investigated a persistent photoconductivity effect which occurred in some of our n-type GaAs samples. We demonstrate that this new metastable phenomena is similar to the DX center persistent photoconductivity which has only been seen in GaAs alloys and stressed GaAs. This new effect in GaAs is not associated with the EL2 defects, although they are also present in the samples. We present evidence that the persistence effect is due to an unidentified defect that undergoes a large lattice relation.

Degree

Ph.D.

Advisors

Bray, Purdue University.

Subject Area

Condensation

COinS