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 GaAs layers grown by molecular beam epitaxy at a substrate temperature of 250°C, under As₄/Ga flux ratios varying from As-rich to stoichiometric growth conditions. Dopant concentrations at or above ∼1×10¹⁹ cm^-3 appear to reduce the incorporation of excess arsenic as both antisite and interstitial defects at all flux ratios at this growth temperature, but only under stoichiometric conditions for Si doping of 1×10 ¹⁸ cm^-3. The effect is attributed to dopant influencing the dissociation of the As₄ molecule and the incorporation of excess As atoms into the crystal. Highly doped n-type material with excellent electrical and optical properties, and high electrical quality p-type material have been achieved by moving towards stoichiometric growth conditions. This is believed to be due to further reduction of formation 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 material.