High-resolution measurements of localized vibrational mode infrared absorption of Si-doped GaAs

The infrared absorption due to excitation of localized vibrational modes (LVM) involving Si impurities in GaAs was measured at 80 K under high-resolution conditions for 1×1018 cm−3≤[Si]≤5×1019 cm−3. Electrical compensation by Li diffusion or electron irradiation resulted in no observable differences in peak positions or linewidths for those LVM identified as SiGa, SiAs, and pair absorptions. These modes (including the individual lines composing the SiAs LVM) had intrinsic linewidths of 0.4 cm−1 which broadened as [Si] increased. In electron irradiated materials, an absorption band with major peaks at 366.63, 368.31, 369.53, and 370.7 cm−1 was seen to shift to lower energies by 9.9 cm−1 when 28Si was replaced with 30Si. Arguments are presented to suggest that the 366.63 cm−1 peak may be due to SiAs paired with a nearest-neighbor native defect such as AsGa or a Ga vacancy. In Li compensated material, the isolated 7LiGa LVM was seen for the first time at 449.64 cm−1 as well as several additional unidentified absorptions. The two bands due to 28SiGa-28SiAs have asymmetrically broadened lines which are attributed to various configurations of nearest neighbor Ga isotopes in the host lattice and the observations are compared to model calculations. Finally, the band associated with 28SiGa-30SiAs and 30SiGa-28SiAs pairs was resolved into a doublet with peaks at 455.80 and 457.01 cm−1, respectively.