EFFECTS OF GROWTH CONDITIONS ON DEEP-LEVEL DEFECTS IN VPE AND LPE GaAs

Studies of the deep-level defects in the VPE and LPE GaAs layers under various growth conditions have been made in this work, using DLTS and C-V techniques. In the VPE grown GaAs, characterization of grown-in defects vs. Ga/As ratio (i.e., 2/1, 3/1, 4/1, and 6/1) were made on GaAs layers grown on , , and substrates. The two common electron traps observed in these samples were due to the EB-4 (i.e., Ec -0.71 eV) level and the EL-2 (i.e., E -0.83eV) level. The density of these two electron traps was found to depend on the stoichiometry as well as substrate orientation. For examples, in the orientation samples, the density of EL2 was found to decrease with increasing Ga/As ratio (e.g., NT = 1.2x1014cm-3 for Ga/As = 2/1, and reducing to 5.4x1011 cm-3 for Ga/As = 6/1). A similar result was also observed in the EB-4 electron trap. Low temperature (230°C) thermal annealing and recombination enhanced annealing studies on these samples showed significant reduction in the density of EB-4 trap and slight reduction in EL-2 trap density. For the LPE grown GaAs layers, two growth temperatures (700 and 800°C) and two temperature dropping rates (l°C/min. and 0.4°C/min.) were used. The DLTS and C-V measurements were made on these samples, and the results showed that only EB-4 electron trap (i.e., Ec-0.71 eV) was observed in the LPE GaAs samples with 1°C/min. dropping rate. Details of our DLTS analysis of the grown-in defects vs. growth conditions in both LPE and VPE grown GaAs layers will be discussed in this paper