Growth and characterization of low defect GaAs by vertical gradient freeze.

As the diameter of GaAs substrates has increased, so has the difficulty and cost of growing GaAs by Liquid Encapsulated Czochralski (LEC). One alternative crystal growth method which offers promise is growth by Vertical Gradient Freeze (VGF). This technique avoids the problems associated with diameter control during low gradient LEC growth. In this paper we discuss the growth of 2 inch diameter undoped and in-alloyed GaAs by VGF. Through the use of low gradients, undoped material with a dislocation density of 2-6 x 10 sup 3 cm sup (-2) has been obtained. With the addition of 0.6 at % InAs to the melt, this density is further reduced to 0-1000cm sup (-2). In contrast to standard LEC, GaAS grown by VGF shows low concentrations of the EL2 deep level and of the C shallow acceptor level. The material is semi-insulating, rho, => 10 sup 7 OMEGA -cm, and is thus suitable to device applications. From temperature dependent Hall measurements, the semi- insulating (Si) behavior is believed to be caused by Fermi level pinning at a defect with an energy level of ~0.5 eV.