Mechanism of Branching and Kinking during VLS Crystal Growth

Abstract

The morphology of the solid-liquid interface and the contact angle configuration of the liquid alloy droplet determine the direction of growth of crystals prepared by the vapor-liquid-solid (VLS) technique. There are four different processes by which both growth kinks and branches can be formed. A change in solid-liquid interface shape during VLS caused by a lateral temperature gradient results in the formation of growth kinks. Branches are formed if the alloy droplet ruptures during the kinking sequence. A sudden increase in temperature can cause an unstable contact angle configuration. The alloy droplet may run down the side faces of the growing crystal, leading to the formation of growth kinks or branches. A sudden decrease in temperature may cause "pinching off" of small droplets from the main droplet, giving rise to branches. Finally, the codeposition of liquid-forming impurities may also lead to branch and kink formation. The proposed models have been verified experimentally for VLS growth of silicon and germanium. Crystalline defects, such as dislocations, are not essential for the branching and kinking process. It is shown that "growth shaping" during the VLS process ispossible.