Incorporation of Thallium in IN1−xTIxP Grown by Metal Organic Molecular Beam Epitaxy

Abstract

ABSTRACTInxTll−xP has been proposed as a potential narrow bandgap material for the fabrication of IR detectors. 1 It is expected to exist in a zincblende structure with a lattice constant approximately 2% larger than aInP for x=0. In this paper we will discuss attempts to grow this alloy on InP using various combinations of elemental and gaseous sources including In, Tl, trimethylindium (TMI), triethylindium (TEI) and phosphine. The sticking coefficient of Tl was found to decrease rapidly for temperatures above 350°C, mandating the use of low temperatures. Attempts to grow TIP resulted in the formation of Tl droplets which oxidized rapidly upon removal from the vacuum system. Auger analysis of the surface shows the oxide composition to be Tl2O, indicative of a monovalent Tl oxidation state. InTlP grown under similar conditions shows an initial tendency to form structural defects, as observed by cross-sectional TEM, suggesting lattice mismatch due to incorporation of small amounts of Tl. As the Tl concentration at the growth surface is increased, a two-phase material is obtained consisting of Tl-rich droplets and InP. In addition, Auger depth profiling shows clear evidence of Tl segregation.