Al_x Ga_1-x As-GaAs Heterojunctions

Abstract

Electrical properties and injection luminescence were studied in Al_x Ga_1-xAs-GaAs n-p and p-n heterojunctions containing various amounts of aluminum (Eg = 1.52–1.9 eV at 300°K). A band model of the heterojunctions was established and its principal parameters were determined. It is shown that the main discontinuity occurs in the conduction band. The size ΔE_c of this discontinuity varies linearly with the aluminum content in Al_x Ga_1-xAs; the discontinuity ΔE_v in the valence band is almost zero. The injection luminescence spectra agree with the proposed model. The mechanism of current flow is compared with features of the electroluminescence spectra. At room temperature and above, the initial (low-current) section, the forward branch of the current-voltage characteristic for n-p heterojunctions is determined by recombination in the space-charge layer, and at current densities above 1–5 A/cm², by recombination in the bulk of the diode. At low temperatures, the forward branch is given by the theory of Shockley, Noyce, and Sah. For p-n heterojunctions, the initial section of the current—voltage characteristic is of the tunnel type; at about 5 A /cm² and above, the mechanism of current flow is similar to that in n-p heterojunctions.