Thermal annealing behaviours of GaP(001) surface

Thermal degradation of GaP(0 0 1) surfaces has been studied using spectroellipsometry (SE), optical microscopy, scanning electron microscopy (SEM), ex situ atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) techniques. The SE data suggest that thermal annealing causes removal of the native oxide at temperatures T < 600 deg. C and surface roughening at T ≥ 600 deg. C. The XPS spectra confirm the native oxide removal from the GaP surface. The AFM images provide rms roughnesses of ∼0.6 nm at T < 600 deg. C and ∼2 nm (∼15 nm) at T = 600 deg. C (800 deg. C), suggesting a rapid increase in the rms roughness with an increase in T above 600 deg. C. The reduction in PL intensity is observed for T ≥ 500 deg. C. The Ga droplets, observed by optical microscopy and SEM, appear at T > 600 deg. C, i.e. after the native oxide is removed from the GaP surface. These facts allow us to draw the conclusion that the surface native oxide acts as a good passivation film against annealing-induced PL degradation and thermal decomposition