Honeycomb voids due to ion implantation in germanium

For future semiconductor devices, germanium layers are very attractive due to their high carrier mobility with ion implantation remaining the dominant method for forming pn junctions. Yet, implantation of heavy ions above a critical dose causes inadmissible surface roughness and formation of voids. To understand the main factors of influence, a comprehensive study on void formation was performed with different ions (BF2, P, Al, Ga, Ge, As, Sb) implanted at various doses, dose rates, and energies. It was found that the dose is the most important parameter for void formation. The critical dose was determined to be 2·1015 cm-2 for As, 2·1015 cm-2 for Ga, and 5·1014 cm-2 for Sb, respectively. For ions with lower mass (BF2, P, Al), no or only negligible surface roughening w as observed.