Electroluminescence of heavily-doped heterojunctions pAlxGa1-xAs-nGaAs

Abstract

There are given results of an investigation of the electroluminescence spectra of heavily- doped heterojunctions pAlxGa1-xAs-nGaAs prepared by liquid epitaxy, as well as some applications of a study of heterojunctions in the system AlAs-GaAs which have led to a creation of injection heterolasers with a low generation threshold at room temperature.In the heterojunctions pAlxGa1-xAs-nGaAs, due to a discontinuity in the conduction band ΔEc equal to the difference in the gap widths of the heterojunction components, one side injection can occur which facilitates an analysis of the mechanisms of current formation and electroluminescence. As shown by a study of the injection luminescence spectra of heavily-doped heterojunctions, depending on the thickness of space charge layer there can occur either thermoinjection filling of “tails” in the density of states in gallium arsenide or “diagonal” tunneling-recombination transitions directly between the electrons of the narrow-band and the holes of the wide-band heterojunction components. The radiation associated with “diagonal” transitions is polarized predominantly parallel to the electric field in the junction. An analysis of the dependences of radiation intensity on current and applied voltage indicates unambiguously an absence of a drop of the quasi- Fermi level at the heterojunction interface.Injection heterolasers representing n-p-p+ structures with heterojunctions in the system AlAs-GaAs have a threshold current density for the best specimens of ≈ 5 × 103 A/cm2 at 300 °K and internal losses of 3 cm-1. Low threshold currents at elevated temperatures and low losses can be attributed to inherent features of the heterolaser structure, viz. the regions of recombination and inverse population coincide and are located in the central narrow-band layer. This is why the recombination and light losses in the passive regions are very small.