High pressure and<i>DX</i>centers in heavily doped bulk GaAs

Abstract

Measurements of the pressure dependence of electron concentration and mobility have been analyzed for heavily doped, bulk GaAs:(Si,Sn,S,Te). It is demonstrated that the samples with n&gt;2\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ exhibit the effect of carrier freeze-out for pressures below 20 kbar. GaAs:Te represents the exception to this behavior (n versus pressure is constant up to 25 kbar). Two models of the localized state of the donor are considered. Neutral, ${\mathrm{DX}}^{0}$, or negatively charged, ${\mathrm{DX}}^{\mathrm{\ensuremath{-}}}$, states might appear after trapping one or two electrons, respectively, by the positively charged donor center. The results obtained show that the energetic level related to the DX center, ${E}_{\mathrm{DX}}$, is located much higher in the conduction band than could be deduced from results extrapolated from ${\mathrm{Al}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ga}}_{\mathrm{x}}$As (${E}_{\mathrm{DX}}$ situated about 170 meV above the bottom of the \ensuremath{\Gamma} conduction band, versus ${E}_{\mathrm{DX}}$&gt;250 meV obtained in this work). The results show that the localized and metastable DX center is not related to any single conduction-band minimum; its energy position and pressure coefficient exhibit significant temperature dependence. For a Si donor in GaAs, weakening of the electron-lattice coupling strength as a result of applying pressure is anticipated. Increase of electron mobility with decreasing carrier concentration has been observed here. Though it is suggestive to use this result for eliminating the concept of the ${\mathrm{DX}}^{\mathrm{\ensuremath{-}}}$ center, some objections to this conclusion, due to possible correlations in dopant distribution, are presented in the paper.