Deep-level transient spectroscopy was used to investigate deep levels in n-type Ru-doped GaAs grown by low-pressure metal-organic chemical-vapour deposition. Deep-level transient spectroscopic scans over a wide temperature range (12 to 470K) revealed 2 prominent deep-level peaks associated with Ru, when compared with control samples with no deliberate Ru-doping. The well-known mid-gap defect EL2 was also observed in these scans. The Ru-related deep levels, Ru1 and Ru2, corresponded to energy positions Ec−0.46eV and Ec−0.57eV in the upper-half band-gap of GaAs. No prominent deep levels associated with Ru were observed in the lower half-bandgap in the injection deep-level transient spectra; only the 3  inadvertent levels already present in the as-grown, control material were observed in these spectra. Although a possible Ru-related peak may be present with a rather small concentration in these injection deep-level transient spectra, it was difficult to clearly identify this peak also present in the control (as-grown, without Ru) samples at a closely similar position. Interestingly, doping with Ru revealed an interesting significant suppression of the pre-existing deep levels, including EL2. Detailed emission rate signatures were presented for the Ru-related deep levels and analyzed to obtain the relevant deep-level characteristics. Both Ru1 and Ru2 were found to show strong dependence on electric field, as demonstrated by the shift in the corresponding deep-level transient spectrum peak positions with the applied reverse bias during electron emission.

Ruthenium Related Deep-Level Defects in n-type GaAs. N.A.Naz, U.S.Qurashi, A.Majid, M.Z.Iqbal: Physica B, 2009, 404[23-24], 4956-8