Brittle-to-ductile transition behavior of gallium arsenide

Gallium arsenide is an important semiconductor compound that is widely used in optoelectronic devices. However dislocations can adversely affect the electronic and optoelectronic properties of GaAs and this makes it essential to understand the dislocation configuration and behavior in this material. A number of researchers have performed such investigations but practically always at high temperatures where the crystal is in the ductile regime. In this study, we employed three techniques to investigate the transition from brittleness to ductility in undoped monocrystalline GaAs.; The first technique was static and dynamic indentation tests over a wide temperature range covering both the brittle and ductile regimes of GaAs. Both types of indentation tests---static as well as dynamic---resulted in an indentation brittle-to-ductile transition temperature TIBDT of around 200-220°C.; The second technique was 4-point bend testing on precracked samples of GaAs. We find TBDT for undoped GaAs to be very sensitive to the strain rate and to range from 300 to 380°C for the strain rate ranging from &egr; =1x10-6s-1 to &egr; = 5x10-5s-1. We also determined the activation enthalpy DeltaHd for dislocation glide to be (1.36+/-0.02) eV.; The third technique was controlled compression experiments to measure the yield stress tau of GaAs at different temperatures and strain rates. At every strain rate studied, the plot of ln(tau) versus 1/T showed a break at a critical temperature T c of around 300-380°C. A comparison of TBDT and Tc shows that these two temperatures are likely identical at any particular strain rate.; Extensive TEM of the deformed samples showed significant differences between the stress-induced dislocations in the two regimes T< TBDT and T>TBDT . The results indicate that in the brittle regime, partial dislocations are nucleated and are responsible for the limited plastic yielding that takes place while in the ductile regime, perfect dislocations are nucleated and their glide results in extensive plastic deformation of the material.