Effects of rapid thermal processing on electron traps in molecular-beam-epitaxial GaAs

Variations of deep levels in Si-doped molecular-beam-epitaxial (MBE) n-GaAs layers by rapid thermal processing (RTP) using halogen lamps were investigated by deep level transient spectroscopy. RTP was performed at 700, 800, and 900 °C with the face-to-face configuration. Native deep levels M1 (Ec−0.18 eV), M3 (Ec−0.33 eV), and M4 (Ec−0.51 eV) in MBE n-GaAs are annealed out by RTP at 900 °C. The metastable electron trap N1 (Ec−0.5∼0.7 eV) and the midgap electron trap EL2 (Ec−0.82 eV) are produced by RTP at 700, 800, and 900 °C. Two electron traps N2 (Ec−0.36 eV) and N3 (Ec−0.49 eV) are produced by RTP at 900 °C. The peculiar spatial distribution of N1 and EL2 are observed across the RTP layers. In particular, the EL2 distribution is found to be a W-shaped pattern. It is supposed that this peculiar shape of the spatial variation is consistent with that of the thermal stress induced by RTP. In addition the spatial variations of EL2 are suppressed by use of the guard ring composed of GaAs pieces, since it prevents the thermal stress during RTP, but EL2 remains at uniform concentration of ∼1014 cm−3 across the RTP layer. It seems that the thermal stress enhances the production of the trap EL2. On the other hand, the trap N1 is found to disappear by the use of the guard ring composed of GaAs pieces. We also discuss the difference of deep levels between MBE and bulk GaAs after RTP.