Identification of the neutral donor molecule in III-V semiconductors

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Abstract
Far-infrared photoconductivity of high-purity n-type III-VI semiconductors has been known to exhibit a sharp peak at an energy of about 60% of the effective Rydberg. The authors have carried out a combined experimental and theoretical investigation of the magnetic field dependence of the spectra for GaAs and InP. While the result positively rules out earlier interpretations in terms of the ionised donor molecule D2+, the 1 Sigma g+-1 Sigma u+ transition of the neutral donor molecule D2 gives a consistent explanation. In particular, the weak magnetic field dependence of the line energy and width is shown to be a consequence of the transition being a charge-transfer excitation where both the initial and the final states derive from the same (1s) donor orbital.