EL2 distributions in vertical gradient freeze GaAs crystals

Abstract

Spatial distributions of EL2 in undoped, semi-insulating GaAs crystals grown by a novel vertical gradient freeze (VGF) method are reported. As a result of the low-temperature gradients present during growth and post-solidification cooling, these crystals exhibit lower EL2 concentrations and lower dislocation densities than liquid-encapsulated Czochralski crystals. Both the EL2 distribution and dislocation density over the area of a wafer do not display the fourfold symmetric pattern prevalent for LEC-grown GaAs. The radial distributions of EL2 in as-grown VGF crystals have been found to be independent of the dislocation density. Axial and radial Hall-effect measurements are included. Thermal activation energies are also presented and the compensation mechanism for this material is discussed.

III–V Technology: The Key for Advanced Devices

“…No point defect segregation at dislocations occurs which enhances the formation of EL2 under conventional growth conditions. Table I gives results after Gray et al (4), and Fig. 1 shows the excellent uniformity achievable from wafer to wafer.…”

“…A new growth method which is in principle a very old one seems to be advantageous: the vertical gradient freeze process (VGF), see (4,5). In this growth method applied to <100> oriented GaAs single crystals, a low thermal gradient is achieved which results in a uniform EL2 distribution.…”