Coexistence of two deep donor states, DX- and DX0, of the Sn donor in Ga1-xAlxAs.

Abstract

We present results of correlated electron-paramagnetic-resonance and photoconductivity measurements on the tin donor in ${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As (0.3x0.7), which demonstrate that the photoionization of the DX center leads to the formation of a localized paramagnetic donor state, ${\mathit{DX}}^{0}$(Sn), according to the reaction ${\mathit{DX}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathit{DX}}^{0}$+${\mathit{e}}^{\mathrm{\ensuremath{-}}}$, in agreement with negative-U models for the DX ground state. The ${\mathit{DX}}^{0}$ state, which has been previously attributed by us to the ${\mathit{A}}_{1}^{\mathrm{ab}}$ antibonding state, is observed only in a limited alloy range 0.3x0.5, where the ${\mathit{DX}}^{0/+}$ level is not resonant with the conduction band. Our results provide a simple explanation for the origin of the intermediate state in the electron-capture process of the single donors, the existence of which has been postulated previously from an analysis of the electron-capture kinetics of the DX center as well as from low-temperature photo-DLTS (deep-level transient spectroscopy) measurements: the one-electron ${\mathit{A}}_{1}^{\mathrm{ab}}$ state. As ${\mathit{A}}_{1}^{\mathrm{ab}}$ states are a fundamental property of substitutional donors, these results are also relevant for the analysis of DX-center properties of the other substitutional donors Si, Se, Te, and S in ${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As.