Effects of rapid thermal processing on molecular‐beam epitaxy GaAs with SiOx encapsulation

Variations of deep levels in Si‐doped molecular‐beam epitaxy (MBE) n‐GaAs layers by rapid thermal processing (RTP) were investigated by deep‐level transient spectroscopy. RTP was performed at 850, 910, and 1000 °C with SiOx encapsulation. Native deep levels M1 (Ec - 0.18 eV), M3 (Ec - 0.33 eV), and M4 (Ec - 0.51 eV) are annealed out by RTP at a higher temperature (1000 °C) compared with the case of capless RTP. Three electron traps NC1 (Ec - 0.36 eV), NC2 (Ec - 0.48 eV), and EL2 (Ec - 0.81 eV) are produced by RTP. After RTP at 850 and 910 °C, the concentrations of the EL2 decrease with depth from the surface and show no peculiar lateral distribution across the wafer, which is different from that of capless RTP reported previously. The formation of the EL2 is enhanced by the stoichiometry change due to the Ga outdiffusion into the SiOx film during RTP. After RTP at 1000 °C, the outdiffusion of the EL2 is observed near the surface. This result seems to be ascribed to the As loss, since it can no longer prevent the As evaporation at such high temperature. Though it has been reported previously that an N1 trap which has a broad energy level (Ec - 0.5–0.7 eV) is formed in MBE GaAs by RTP without any encapsulation, no N1 trap was observed in a SiOx‐capped sample after RTP. We discuss the difference of the EL2 concentration depth profiles between SiOx‐capped MBE GaAs and capless samples after RTP, considering the absence of the trap N1 in capped samples.