A Thermoelastic Analysis of Dislocation Generation in Pulled GaAs Crystals

A number of recent papers have shown that the performance of GaAs-based devices is adversely affected by dislocations. For example, Brantley and Harrison 1 have observed that the degradation rate in diffused electroluminescent diodes increased by an order of magnitude, and was accompanied by dislocation generation, during forward bias aging when a compressive load was also applied. Subsequently, Zaeschner 2 has found that external stress alone is sufficient to cause diode degradation and gave a quantitative account of the change in light output with time in terms of the kinetic properties (multiplication and velocity) of dislocations, considered to be nonradiative recombination centers. Even in the absence of deliberately imposed forces, a large enough density of grown-in dislocations in GaAs alters device behavior. In particular, very recently Roedel et al'1 have correlated the reduction in external quantum efficiency of Si-doped GaALAs LEDS with increasing dislocation density and established that these defects act as nonradiative recombination centers. Moreover, the dislocation density in the GaAlAs epitaxial layer essentially duplicated that of the GaAs substrate. Therefore, in view of its importance, we have undertaken an investigation of the primary cause for the generation of dislocations in GaAs substrates grown by the Czochralski technique and then attempt to employ this knowledge in suggesting growth conditions which facilitate the elimination or at least reduction of these defects.