Radiation Enhanced Dislocation Glide and Rapid Degradation
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RADIATION ENHANCED DISLOCATION GLIDE AND RAPID DEGRADATION MAEDA K. YAMASHITA Y. MAEDA N*. AND TAKEUCHI S* Department of Applied Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, Japan *The Institute for Solid State Physics, The University of Tokyo, Roppongi, Minato-ku, Tokyo, Japan ABSTRACT Conspicuous enhancement of dislocation glides under minority carrier injection is reviewed. Systematic investigation of dislocation glide velocity under electron-beam irradiation in various semiconducting crystals showed that the radiation enhanced dislocation glide (REDG) effect exhibits features expected from the recombination enhanced defect motion (REDM) mechanism. Theoretical analysis, based on the kink diffusion model for the elementary process of dislocation motion, shows that the REDG effect requires enhancement of double-kink formation. An experimental attempt provided an evidence for the smallest double kink formation is the only process that is enhanced by carrier injection. In light of the knowledge available at present, a guide line in device design to minimize degradation in the dislocation glide mode is suggested. INTRODUCTION In the early stage of development of laser diodes (LD) and light emitting diodes (LED), evidences for enhanced dislocation glides were accumulated: TEM observations [1] revealed that dark line defects (DLDs) that stretch along directions in degraded GaAlAs/GaAs DH lasers grown on a (001) plane are lying on (1111 glide planes. It was also found that not only forwardbiased current [2] but also laser illumination (3-5] and electron-beam irradiation (6], all of which inject minority carriers into the crystal, stimulates dislocation glides. Similar effect was observed in various materials under various injection conditions (7-9]. However, since those experiments had been conducted in complex device structures or under poorly defined stress conditions, quantitative aspects of the effect remained unclear until later systematic measurements were performed for single crystals under simpler experimental conditions [10-12]. In practical devices, the problem of rapid degradation in the dislocation glide mode as well as in the climb mode was solved in the fabrication technology by removing threading dislocations in epitaxial layers which act as sources of later dislocation multiplication. However, the mechanism of the enhanced dislocation motion in operating devices is not yet completely understood. Many devices currently under development possess heterogeneous structures in which the stress, the primary motive force to drive dislocation motion, is so high that dislocations can glide more easily in less intensive conditions: To circumvent this problem, we will need some new technological measure and elucidation of the mechanism of degradation, especially at the microscopic level, will be useful to serve as a guide line in designing new devices on a sound theoretical basis. This article first reviews experimental features of the radiation enhanced dislocation glide (REDG) effect so far revealed,
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