Ion-beam-induced isolation of GaAs layers by4He+implantation: effects of hot implants

The formation of thermally stable highly resistive regions in n-type GaAs layers during helium ion bombardment at elevated temperatures, where dynamic annealing of radiation-induced defects is substantial, was investigated and presented here. The substrate temperatures were chosen to be room temperature (RT), 100 and 200 °C. Semi-insulating GaAs wafers of (100) orientation were implanted with multi-energy 29Si atoms to create a flat dopant distribution of about 0.7 µm in thickness. A uniform damage density was formed within the conductive layer by 2×1014 cm-2 helium implantation at 600 keV to isolate the structure. Resistivity and Hall measurements were performed in order to study the evolution of the sheet resistance and Hall mobility as a function of post implant annealing temperature in these resistors implanted at three different temperatures. The samples were annealed in the range 100-800 °C and an optimum isolation of >107 ohms/□ was achieved for samples implanted at either RT or elevated temperatures after annealing at 400 or 450 °C, respectively. Annealing at higher temperatures returned the resistivity to a value close to that of the starting material and it was found that RT implants recover quicker than elevated temperature implants. The isolated regions exhibited good stability to heat treatment up to 550 or 650 °C for 100 or 200 °C implants, respectively. No such annealing window for the thermal stability of the obtained isolation was found for samples implanted at room temperature. It is believed that isolating defects are more thermally stable in the case of hot implants than those formed by RT implantation.