Defects and ion redistribution in implant-isolated GaAs-based device structures

Implant isolation of thick GaAs based epitaxial structures using either multiple energy keV ions or a single MeV ion implantation is becoming more popular for devices such as heterojunction bipolar transistors or quantum well lasers. We report examples of both types of isolation schemes, using keV F ⁺ and H⁺ ions, or MeV O⁺ ions. Post-implant annealing at temperatures in the range 500-600°C is needed to maximize the resistivity of the implanted material, but this causes redistribution of both F and H (but not O) and accumulation of hydrogen at strained or ion-damaged interfaces. The amount of hydrogen motion is sufficient to cause concerns about dopant passivation occurring in the initially masked, active regions of the devices. The resistance of the ion-implanted regions is stable for periods of ≥50 days at 200°C, and is controlled by deep level point defects which pin the Fermi level near mid gap.