STOICHIOMETRIC DEFECTS IN SEMIINSULATING GAAS

The influences of arsenic interstitials and dislocations on the lattic e parameters of undoped semi-insulating (SI) GaAs single crystals were analyzed. It was shown that the dislocations in such crystals serve a s effective gettering sites for arsenic interstitials due to the defor mation energy of dislocations. The average excess arsenic in GaAs epil ayers grown by molecular-beam epitaxy (MBE) at low temperatures (LT) i s about 1%, and the lattice parameters of these epilayers are larger t han those of liquid-encapsulated Czochralski-grown (LEG) SI-GaAs by ab out 0.1%. The atomic ratio, [As]/([Ga] + [As]), in SI-GaAs grown by lo w-pressure (LP) LEC is the nearest to the strict stoichiometry compare d with those grown by high-pressure (HP) LEC and vertical gradient fre eze (VGF). After multiple wafer annealing (MWA), the crystals grown by HPLEC become closer to be strictly stoichiometric.