Dependence of the Sn^0/2+ charge state on the Fermi level in semi-insulating CdTe

Abstract

We explored the growth and characteristics of CdTe doped with Sn to heighten our understanding of the role of deep levels on electrical compensation and trapping. We demonstrated, for the first time, the strong dependence of the Sn Cd charge state on the Fermi-level variation (2-3kT) in high-resistivity CdTe. The concentration of deep traps for electrons was determined by the number of doubly positively charged Sn 2+ atoms. Thermoelectric-effect spectroscopy and photovoltage measurements revealed the conversion of the Sn Cd defect from the electron Sn Cd 2+ trap to the hole Sn Cd 0 trap. The results agree well with the existence of a negative U-center in the Sn Cd 0/2+ defect. We also showed that the neutral Sn defect is responsible for the near midgap C-band → bound hole radiative transitions band with a maximum at 0.76 eV.

Photoluminescence and electric spectroscopy of dislocation-induced electronic levels in semi-insulated CdTe and CdZnTe

“…Ten samples of 5 Â 8 Â 1 mm 3 were cut from the middle of the several ingots, mechanically lapped, polished, and finally chemo-mechanically polished with a Br/methanol solution. We applied several techniques to characterize the material's properties, -non-contact measurement of dark resistivity and photosensitivity, low-temperature PL, and TEES [15]. The PL spectra were obtained with Si, Ge, or InSb detectors in the spectral region of 0.5-1.8 eV at 4.2 K in an in-flow cryostat using an Ar laser beam (488 nm, 20 mW) focused on to a 50 mm diameter spot.…”

Compensation and trapping in large bandgap semiconductors: Tuning of the defect system in CdZnTe

“…We demonstrated previously [3,11,12] that a small variation of the deep-donor level position with respect to the Fermi level can raise electron trapping by approximately 5-10 times.…”

Characterization of compensation and trapping in CdTe and CdZnTe: Recent advances

“…This requirement is very difficult to satisfy because the chemical origin of such defects still is debatable, and the precise concentration of deep levels is unknown. The best known and controlled deep electronic levels in the CdTe or CZT materials are generated by doping with impurities, such as Ge, Sn, Bi or V, but some can be ascribed to native defects, e.g., V Cd and Te Cd , or dislocation-induced energy levels [9][10][11][12][13][14][15][16][17][18][19]. [20].…”

“…Table 1 summarizes the properties of these deep levels, wherein Eg(CdTe) =1.48 eV at room temperature. [9] p or n [10] p or n n p n Ionization energy Et (eV)…”

“…EC-0.86 [9] EC-0.75 [10] EV+0.55 [11] EV+1.4 (calc) [13] EV+0.71 [14] EV+0.95 [15] EV+(0.03-0.1) (calc) [16] EV+0.73 (assumed) [17] <(EV+0.47) [18] EV+0.74 (assumed) [17,5] EV+0.35 (calc) [19] Capture cross-section σ (cm 2 )…”