CONCENTRATION-DEPENDENCE OF OPTICAL-ABSORPTION IN TELLURIUM-DOPED GASB

The optical absorption of molecular-beam-epitaxy-grown and Te-doped Ga Sb layers is measured in the spectral region of the fundamental absorp tion over a temperature range extending from 10 K to 300 K. In accorda nce with the Burstein-Moss description, a filling of the conduction-ba nd states, resulting in a change of the shape and a shift of the absor ption edge to higher energies, is observed in the absorption spectra o f Te-doped n-type GaSb layers, with electron density ranging from 1.1 x 10(16) to 7.6 x 10(17) cm(-3) at room temperature. A quantitative de scription of the Burstein-Moss effect is performed and the Fermi-level energy and the electron density in the Gamma valley are obtained as a function of the temperature in two different ways: (i) by comparing a bsorption spectra of heavily doped and unintentionally or lightly dope d 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 Gamma valley which have been optically obtained resulted in satisfactory agreement with those obtained from e lectrical measurements. The bandgap narrowing and the perturbation of the conduction-band density of states due to heavy doping in small-eff ective-mass semiconductors, such as GaSb, is considered in the framewo rk of some current theoretical models.