STARK-BROADENING OF IMPURITY ABSORPTION-LINES BY INHOMOGENEOUS ELECTRIC-FIELDS IN HIGHLY COMPENSATED GERMANIUM

Stark broadening of Zeeman absorption lines caused by inhomogeneous el ectric fields in highly compensated Ge has been studied by means of fa r-infrared magneto-optical absorption spectroscopy measurements. A num ber of transmutation-doped Ge single crystals with a systematically va rying compensation ratio were employed. The broadening of the full wid th at half maximum (FWHM) of an absorption line of the Ga acceptor is studied as a function of excitation light intensity with above-band-ga p energy. The FWHM increases with decreasing intensity of the band-edg e light excitation. Observation of the theoretically predicted 4/3-pow er law of Stark broadening, due to ionized impurities, is reported. Th e line broadening originates in the Stark affect, due to inhomogeneous electric fields caused by the random distribution of ionized impuriti es. In order to understand the mechanism for the line broadening in de tail, a numerical approach based on a Monte Carlo simulation has been performed. The results of this simulation show that the inhomogeneity of the field distribution becomes larger with increasing concentration of ionized impurities. The simulation based on a perfectly random dis tribution for an initial impurity arrangement gives a Fairly good agre ement with the experimental results. We conclude that the distribution of impurities in transmutation-doped Ge samples is close to random.