Chemistry of arsenic incorporation during GaAs/GaAs(100) molecular beam epitaxy probed by simultaneous laser flux monitoring and reflection high-energy electron diffraction

Abstract

Arsenic incorporation during GaAs/GaAs(100) molecular beam epitaxy is studied in situ with laser single-photon ionization time-of-flight mass spectrometry and reflection high-energy electron diffraction (RHEED). Incident and scattered fluxes of Ga and Asn species in front of the growing GaAs wafer are ionized repetitively by a pulsed laser beam of 118 nm (10.5 eV) photons. The methods to obtain and interpret time-of-flight mass spectra and the simultaneous RHEED measurements are described. The real time behaviors of incident Ga and desorbing As2 and As4, obtained without mass spectral cracking, are studied during growth of GaAs layers with As4 and when growth is arrested as a function of substrate temperature and Ga/As4 flux ratio. During growth only with As4, both As2 and As4 are desorbed or scattered in varying amounts depending on flux and substrate temperature conditions. Without an incident gallium flux, desorbing As4 decreases while desorbing As2 increases with increasing surface temperature. During gallium deposition and GaAs growth, the amounts of desorbing arsenic fluxes decrease linearly with increasing Ga/As4 flux ratio, but the arsenic incorporation rate saturates at a Ga/As4 flux ratio ≥2, i.e. (Ga/As≥1/2). The total integrated incorporation of arsenic increases linearly with increasing Ga/As4 flux ratio when the surface is allowed to recover with an incident arsenic flux after the gallium flux is terminated. In the range of substrate temperatures optimum for layer-by-layer GaAs growth with As4, As4 incorporation dominates at low temperatures, while As4 and As2 incorporations contribute equally at high temperatures. Surface reaction sequences and mechanisms of arsenic incorporation are discussed and compared with measured RHEED results and previous experimental and theoretical results.