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: 5x107 ohmecm (seed part) and 6x105 ohmcm (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.

DSL Photoetching: Principles and Application to Study Nature of Defects in III-V Materials

“…During movement the dislocations interact with the point defects and leave behind deep nonradiative centres, as was recognized by high spatial resolution photoluininescence [19,22]. These traces are etched slower under illumination due to recombination of photogenerated carriers.…”

“…Both phenomenology of the DSL system [12][13][14] and mechanism of dissolution of GaAs [8,16] were described in detail. More recent studies of different types of inhomogeneities of GaAs crystals using the DS(L) and other stuctural methods [17][18][19][20][21][22][23] allow one to formulate some principles of formation of defect-related etch features. These are summarized below.…”

“…In this case the recombinative properties of Cottrell atmospheres decide the shape of dislocation-related etch features. The most clear evidence of the role of light was registered after photoetching of n-type Si-doped GaAs grown from As-and Ga-rich melts [18][19][20]22] and is summarized in Fig. 4.…”

“…The effect of gettering by the dislocation of n-type dopant to form local n+ area may additionally contribute to the formation of hillocks by a decrease of w", as was discussed earlier in this section. When the Cottrell atmospheres are dominated by acceptor-type defects, with a simultaneous decrease of n-type doping [20,22], the amount of holes increases locally and the atmospheres are etched at a higher rate than the matrix (Fig. 4(b)).…”