P Vacancy Assisted In-Ga Interdiffusion

Rachel S. Goldman

Maria Goeppert Mayer Collegiate Professor


2094 H.H. Dow
T: (734) 647-6821




Research Facilities


We are interested in the mechanisms of solute atom incorporation and alloy decomposition in dilute and concentrated semiconductor alloys, respectively. For example, we are exploring the effects of surface reconstruction during thin film growth on the incorporation of solute atoms and other point defects in semiconductor alloys with dilute concentrations of unusual impurities. In dilute GaAsN alloys, conflicting results have been reported regarding the mechanism of N incorporation. Our studies reveal a surface reconstruction-dependent incorporation of N, where substitutional N incorporation is maximized for those reconstructions with a high number of group V sites per unit area, presumably due to the increased availability of group V sites for N-As surface exchange. Indeed, preliminary in-situ STM studies suggest that N atoms tend to occupy interstitial sites at the earliest stages of growth. Interestingly, our measurements of stress evolution in GaAsN alloys indicate significant bowing of the elastic properties of GaAsN, presumably due to the small N atomic size. In dilute GaMnAs alloys, we have quantified the Mn-composition dependence of the concentrations and distributions of point defects in alloys grown at low temperatures. Our cross-sectional STM studies reveal anti-clustering of nearest M-M pairs, suggesting that the attractive interaction expected from the neighboring ionized impurities may be overcome by a magnetic interaction. Our future plans include examining the effects of various point defect concentrations (controlled via growth conditions) on the distributions of Mn in GaMnAs and N in GaAsN, for example.In concentrated (non-dilute) semiconductor alloys, including films AB and superlattices A/B/A/B, spontaneous lateral phase separation often leads to the formation of lateral superlattices consisting of alternating A- and B-rich layers. To date, the relative roles of morphological undulations and random compositional non-uniformities in the initiation of alloy phase separation are the subject of continued debate. In heteroepitaxial semiconductor alloy films, we suggested that phase separation is a misfit-driven kinetic process, initiated by random compositional variations that later develop into coupled compositional variations and morphological undulations. In the case of short-period superlattices, we reported the first direct observation that phase separation is initiated in the first atomic layer in contact with a buffer. These mechanisms are likely to be applicable to a wide range of lattice-mismatched thin film systems. Our future plans include examining the detailed mechanisms of alloy decomposition in other materials systems in order to develop predictive models of alloy phase separation.