Electrical isolation of n-GaAs by proton implantation - effects of doping implant, isolation implant and implant temperature

An effective and reliable technology for device isolation in III-V semiconductors is an essential requirement for the better efficiency and throughput of a number or commercial devices such as ICs, HBTs, HEMT, lasers, LEDs and MMICs. We report on the effects of doping implants, variable doses for isolation implants and variable substrate temperature during implantation on the achieved electrical isolation in n-type GaAs layers using proton bombardment. The starting material was prepared using multi-energy ²⁸Si ion implantation into semiinsulating GaAs at various doses to form n-type GaAs layers of different initial sheet carrier concentration. The isolation was obtained by proton irradiation at a suitable energy to place the peak of the damage distribution well inside the semi-insulating GaAs substrate and a constant level of damage in the near surface device region. Isolation implants were performed at variable doses from 10¹² - 10¹⁶ ions-cm^-2 at room temperature (RT). One particular set of samples was implanted with variable doses at liquid nitrogen temperature and temperatures ranging from RT to 300°C. The threshold dose to convert a conductive layer to a highly resistive one and respective sheet resistivities are found to be different for different initial sheet carrier concentration. The stability and value of isolation is also dependent on the implant temperature. Hot implants at 250 or 300°C, due to their enhanced dynamic annealing and nature of formed trap structures during implantation show better stability of isolation values for a range of doses without any post-implant annealing. The as-implanted sheet resistivity achieved in hot implantation cases is comparable to semi-insulating GaAs resistivities. These results are important in order to choose