Structural and electrical characteristics of undoped LEC GaAs crystals grown from slightly Ga-rich melts: a new approach

Abstract

Undoped GaAs crystals were grown by LEC method from Ga-rich melts with the initial composition above the critical value for transition from S.I. to p-type material. The typical resistivity values measured on these crystals were: 5x10/sup 7/ ohm-cm (seed part) and 6x10/sup 5/ ohm.cm (main body). Samples with these different characteristics were subjected to detailed studies including DSL photoetching, TEM, SRPL, LST and IR absorption. Remarkable differences were found between the high and low resistivity parts of the ingots relating to structural and optical properties. A model is presented based on the concept of the temperature-time-transformation (TTT) diagram, which explains the solid-state phase transitions. Seemingly conflicting results about the increasing EL2 concentration along the ingot axis are explained in terms of competition between formation of EL2 and arsenic precipitates. The present results indicate that the position of the congruent melting point is on the As-rich side of the phase diagram.