Time‐ and bias‐dependent effects in ZnCd(Mg)Se blue and red quantum well light emitting diodes studied by cathodoluminescence

Abstract

Luminescence variations in MBE-grown blue and red ZnCd(Mg)Se/InP QW LEDs have been studied by time-resolved and bias-dependent cathodoluminescence (CL) spectroscopy. CL from the red LED reversibly increased under forward bias and decreased under negative bias during several complete biasing cycles. CL from blue LEDs was bias dependent only during the first few cycles. The irreversible effects were QW CL intensity decreases after electron bombardment for the red LED and QW CL intensity enhancements seen as bright regions in CL images and dark regions in SE micrographs for blue LEDs. For the red LED, the bombarded regions were dark in CL images and had a dark dot and halo contrast in SE micrographs. The enhancements of CL intensity in the blue LEDs may result from buildup of internal fields due to persistent charge trapping in preexisting or electron bombardment created defects. 1 Introduction ZnSe-based chalcogenides are promising materials for short wavelength light emitting diodes (LEDs) and lasers for higher density optical disk information storage systems, full-color projection displays, traffic signals, and efficient white light sources. Despite significant progress in the materials development, commercially successful devices have not been yet achieved because of gradual luminescent intensity degradation during device operation.Since operation of electron devices requires application of electric fields, it is necessary to understand the effects of bias on luminescence and carrier transport. It may also help in further improvement of performance and lifetimes of QW-based light emitting diodes (LEDs) and laser diodes. The present paper describes effects observed during bias cycling cathodoluminescence (CL) experiments on red and blue ZnCdMgSe-based QW LEDs.