Analysis of frequency characteristics of AlGaAs double heterostructure LEDS with a small energy-gap difference at the p-n junction

Abstract

In this paper the electroluminescence (EL) spectra and frequency characteristics of AlGaAs DH LEDS are studied experimentally and theoretically as functions of the energy-gap difference at the p-n junction, the driving current and the doping concentration in the p active layer. Analyses are carried out taking into account the high injection of carriers and the injection of both electrons and holes. The EL analysis reveals that the recombination region varies from the n layer to the p layer as the energy-gap difference at the p-n junction increases from zero to a few kT, for LEDS with n0=5*1017 cm-3, p0=2*1018 cm-3. Then the cut-off frequencies of the LEDS increase with the energy-gap difference, reflecting the change in the recombination ratios in the n and p layers with the energy-gap difference, and the difference in the carrier lifetimes in the two layers. The cut-off frequency of the DH LEDS is almost independent of the driving currents but shows a slow increase for acceptor concentrations of a few times 1018 cm-3. Effective recombination coefficients whose value decreases with injection carrier concentration can explain the experiments well.