Electrical isolation of n-type InP layers by helium implantation at variable substrate temperatures

The electrical isolation in n-type InP layers produced by helium bombardment was investigated for substrate temperatures: room temperature (RT). 100 and 200 degreesC. Semi-insulating InP wafers of (10 0) orientation with Fe doping were implanted with multi-energy Si-2x atoms to create a flat dopant distribution. A uniform damage density was formed within the conductive layer by 2 x 10(14) cm(-2) helium implantation at 600 keV to isolate the structure. Hall effect and resistivity measurements were performed in order to study the evolution of the sheet resistivity in n-type InP layers implanted at three different temperatures and the stability of the formed isolation during post implantation annealing. An isolation resistance of more than 10(6) Omega/square was achieved for as-implanted material. The samples were annealed in the range 100-800 degreesC and an optimum isolation of similar to10(7) Omega/square was achieved for samples implanted at either RT or elevated temperatures after annealing at 400 degreesC. Annealing at higher temperatures returned the resistivity to a value close to that of the starting material and this recovery of conductivity was similar for all three cases. The isolated regions exhibited good stability to heat treatment up to 500 degreesC and again this annealing window for the thermal stability of the obtained isolation was the same for all cases irrespective of the irradiation temperature. Based on the obtained data we infer that for this particular isolation scheme, the implantation fluence is at its threshold. This provides optimum isolation and quite broad thermally stable region due to the formation of such defects during implantation, which are stable to higher annealing temperatures. This data also suggests that for this scheme, the implant temperature is an insensitive parameter. The magnitude of isolation and its characteristic curves in this case are very much similar to p-type InP. which is known to behave differently from n-type InP. This feature makes the data technologically relevant and may have some ramifications for the device engineering industry. (C) 2002 Elsevier Science B.V. All rights reserved.