Band-gap shrinkage of semiconductors

Abstract

Direct experimental evidence of band-gap shrinkage due to the presence of impurities in semiconductors is given. Experimental results are obtained using a piezomodulation-spectroscopy technique over the (4-300)°K temperature range. They are interpreted in the linear-screened-potential and effective-mass approximations. Coupling spectroscopic and helium-temperature magnetotransport measurements allowed us to obtain in this model a good description of the transition edges over the entire temperaure range. We studied different GaSb samples with impurity concentration allowing us to observe band-gap shrinkage with one and two types of carriers. This is easily obtained in the GaSb case whose band structure presents $\Gamma$ and $L$ minima located very near in energy. On heavily doped samples, the low-temperature values of the band-gap shrinkage are used to obtain further informations concerning subsidiary minima. On lightly doped semiconductors, non-$k$ -conserving transitions initiating on the residual acceptor level are clearly shown.