Effects of confined donor states on the optical and transport properties of orderedGaInP2alloys

Abstract

We report properties of long-range-ordered ${\mathrm{GaInP}}_2$ alloys as a function of temperature by a combination of photoreflectance (PR), photoluminescence (PL), and Hall–van der Pauw measurements. Below T=200 K the optical and transport properties are strongly influenced by a donor state, which, owing to confinement in the ordered domains, has a large binding energy of 36 meV. Evidence for strong localization was obtained for T<30 K: the PR spectra showed a pronounced first-derivative line shape at the same energy where PL emission occurs, the conductivity was dominated by hopping (${\mathrm{\epsilon }}_3$) conduction, and the temperature dependence of the PL intensity was consistent with localized states. Between 30 and 70 K the dominating conduction mechanism was identified as ${\mathrm{\epsilon }}_2$ conduction via negatively charged donors: the ${\mathit{D}}^{\mathrm{-}}$ band. At 70 K, Hall data showed a changeover from ${\mathrm{\epsilon }}_2$ to band conduction. It is proposed that the origin of the inverted-S shape of PL energy as a function of temperature is connected with thermal population of the ${\mathit{D}}^{\mathrm{-}}$ band. In the entire T interval between 30 and 200 K, the PR spectra showed a complex line shape owing to the absence of carriers in the disordered regions. Above T=200 K pronounced effects of cluster scattering are observed in the Hall mobility. Supported by data from PR and PL, this shows that carriers are then present in both ordered and disordered regions of the epilayer.