Controlled surface diffusion in plasma-enhanced chemical vapor deposition of GaNnanowires

Abstract

This study investigates the growth of GaN nanowires by controlling the surface diffusion ofGa species on sapphire in a plasma-enhanced chemical vapor deposition (CVD)system. Under nitrogen-rich growth conditions, Ga has a tendency to adsorb onthe substrate surface diffusing to nanowires to contribute to their growth. Thesignificance of surface diffusion on the growth of nanowires is dependent on theenvironment of the nanowire on the substrate surface as well as the gas phasespecies and compositions. Under nitrogen-rich growth conditions, the growth rate isstrongly dependent on the surface diffusion of gallium, but the addition of 5%hydrogen in nitrogen plasma instantly diminishes the surface diffusion effect.Gallium desorbs easily from the surface by reaction with hydrogen. On the otherhand, under gallium-rich growth conditions, nanowire growth is shown to bedominated by the gas phase deposition, with negligible contribution from surfacediffusion. This is the first study reporting the inhibition of surface diffusion effects byhydrogen addition, which can be useful in tailoring the growth and characteristics ofnanowires. Without any evidence of direct deposition on the nanowire surface, galliumand nitrogen are shown to dissolve into the catalyst for growing the nanowiresat 900 °C.