EFFECT OF AS4 GA FLUX RATIO ON ELECTRICAL AND OPTICAL-PROPERTIES OF LOW-TEMPERATURE GAAS GROWN BY MOLECULAR-BEAM EPITAXY/

Hall-effect, near-band-edge infrared absorption, and photoluminescence measurements have been carried out on undoped and Si- and Be-doped Ga As layers grown by molecular beam epitaxy at a substrate temperature o f 250-degrees-C, under As4/Ga flux ratios varying from As-rich to stoi chiometric growth conditions. Dopant concentrations at or above approx imately 1 X 10(19) cm-3 appear to reduce the incorporation of excess a rsenic as both antisite and interstitial defects at all flux ratios at this growth temperature, but only under stoichiometric conditions for Si doping of 1 X 10(18) cm-3. The effect is attributed to dopant infl uencing the dissociation of the As4 molecule and the incorporation of excess As atoms into the crystal. Highly doped n-type material with ex cellent electrical and optical properties, and high electrical quality p-type material have been achieved by moving towards stoichiometric g rowth conditions. This is believed to be due to further reduction of f ormation of compensating defects, Ga vacancies in the n-type case, As antisites in the p type. A photoluminescence peak at 1.24 eV suggests the formation of Si(Ga)-V(Ga) pair defects in the highly Si-doped mate rial.