Concentration dependence of optical absorption in tellurium-doped GaSb

The optical absorption of molecular-beam-epitaxy-grown and Te-doped GaSb layers is measured in the spectral region of the fundamental absorption over a temperature range extending from 10 K to 300 K. In accordance with the Burstein - Moss description, a filling of the conduction-band states, resulting in a change of the shape and a shift of the absorption edge to higher energies, is observed in the absorption spectra of Te-doped n-type GaSb layers, with electron density ranging from to at room temperature. A quantitative description of the Burstein - Moss effect is performed and the Fermi-level energy and the electron density in the valley are obtained as a function of the temperature in two different ways: (i) by comparing absorption spectra of heavily doped and unintentionally or lightly doped GaSb samples; (ii) through a direct fit of absorption data performed in the framework of Kane's band model. The values of the Fermi level and of electron density in the valley which have been optically obtained resulted in satisfactory agreement with those obtained from electrical measurements. The bandgap narrowing and the perturbation of the conduction-band density of states due to heavy doping in small-effective-mass semiconductors, such as GaSb, is considered in the framework of some current theoretical models.