Dislocation studies in 3-inch diameter liquid encapsulated Czochralski GaAs

Abstract

Listen

Translate article

We have characterized the density and distribution of dislocations in 3-inch diameter, undoped GaAs crystals grown by the liquid encapsulated Czochralski technique. The radial distribution across wafers follows a “W”-shaped profile indicating excessive thermal gradient-induced stress as the primary cause of dislocations. The density along the body of each crystal increases continuously from front to tail. In contrast, the longitudinal distribution in the cone region is inverted, first increasing, and then decreasing as the crystal expands from the neck to full diameter. Growth parameters favoring reduced dislocation densities include good diameter control, the use of thick B 2O 3 encapsulating layers, slightly As-rich melts, and low ambient pressures. The dislocation density in the body of the crystal is practically independent of cone angle Θ for 20° < Θ < 70°. However, high densities result for flat-top (0° < Θ < 20°) crystals. Dash-type seed necking works to reduce the dislocation density only when high-density seeds (>5000 cm -2) are used. Dislocation densities below 1X10 4 cm -2 can be achieved routinely in the large annulus region at the front of a crystal through proper control of these parameters. The lowest measured dislocation density was 6000 cm -2. Further, we show that convective heat transfer from the crystal to the high pressure ambient plays a dominant role in controlling the dislocation density.