Laser ionization measurements of gaseous gallium atom desorption from GaAs(100) during molecular beam epitaxy

The desorbed fluxes of gallium atoms from a GaAs(100) substrate during GaAs growth in the temperature range 550 to 1015 K are directly measured with laser single-photon ionization time-of-flight mass spectrometry (SPI-TOFMS). At substrate temperatures above 900 K, Ga atoms desorb from the bulk GaAs wafer. The activation energy for this desorption under neither an incident As nor Ga flux is 4.7 ± 0.2 eV. Under an incident As4 flux, the measured activation energy for Ga desorption from the bulk is 5.2 ± 0.2 eV. At substrate temperatures between 600 K and 900 K, scattered gallium atoms are detected during GaAs homoepitaxy with incident As4 and Ga fluxes. The flux of Ga atoms increases with increasing GaAs surface temperature, but no flux is observed when the Ga oven shutter is closed. Simultaneous measurements of reflection high-energy electron diffraction (RHEED) specular beam intensity oscillations and scattered As2 and As4 mass signals are recorded. The sticking probability of Ga atoms during GaAs homoepitaxy derived from the RHEED results is found to decrease from unity to 0.92 ± 0.02 with increasing temperature. The desorbing flux of Ga atoms linearly increases with incident Ga flux and is not appreciably affected by changes in the incident As4 flux. A precursor mediated adsorption model for Ga atoms on GaAs(100) is discussed to interpret the results.