Irreversible Changes in the Properties of an Injection Laser at High Excitation Levels

Abstract

An investigation was made of gallium arsenide laser diodes prepared by the diffusion of zinc into n-type crystals. The measurements were carried out at liquid nitrogen temperature. An experimental comparison was made of the nature of the reduction in the output laser pulse power with the nature of the reduction in the continuous luminescence intensity during irreversible changes under constant forward bias conditions. This was done in order to determine the role of the shunting of a p-n junction. It was found that such shunting had little influence on the process of reduction of the injection laser efficiency. A study was also made of the watt-ampere characteristic of a laser diode before and after the application of pulses of critical amplitude causing irreversible changes. The difference between the characteristics was attributed to the formation of pits on the resonator face, which were aligned along the p-n junction. Photomicrographs were obtained of the end of a laser diode and of a diode with only one reflecting face. Pits along the p-n junction were observed also for the latter diode and, therefore, it was concluded that the pitting was not related in an unambiguous manner to the critical density of laser radiation. The appearance of pits was attributed to the thermoelastic stresses generated in a diode during a single pulse. A nonlinear watt-ampere characteristic was obtained after the application of strong current pulses. The original characteristic was linear. This was attributed to the formation of cracks which opened up only during pulses.