Degradation induced changes of characteristic parameters of GaAs:Si infrared emitting diodes

Abstract

Characteristic features of GaAs:Si infrared (IR) emitting diodes were measured on virgin samples and on the same samples after 1000 h of operation at 220 A/cm 2 current density. The investigations comprise electroluminescence and cathodoluminescence, lifetime of minority carriers, quantum efficiencies and electron beam induced current (EBIC) spectra. The samples were taken from wafers particularly selected to exhibit relatively strong degradation in order to get more pronounced ageing effects. The most significant changes observed after degradation are a decrease of the minority carrier lifetime τ by about 50% (typical values τ(0) = 350 ns, τ(1000 h) = 190 ns) and a decrease of the external quantum efficiency η by approximately 60% (mean values: η(0) = 7%, η(1000 h) = 2.8%), while the injection efficiency η inj remains constant. The difference in relative change of the external quantum efficiency (−60%) and that of the bulk efficiency (−50%) is shown to be due to reabsorption effects. Reabsorption does also affect the EBIC spectra, in particular those measured on the p-side and thus impairs a reliable derivation of diffusion lengths. Nevertheless our experiments clearly show that degradation is homogeneous in vertical direction all over the IREDs. The results rule out recombination enhanced defect reactions as a relevant source for degradation and on the other hand suggest, that dislocations are likely to be important, which start from the substrate or from the n-layer and penetrate the whole IRED.