Formation of p sup + and high resistivity regions in AlGaAs- GaAs heterostructures.
08 September 1986
Two important steps in the fabrication of heterojunction bipolar transistors (HBTs) in the GaAs-AlGaAs system are the formation of P sup + contacts to the base layer, and semi-insulating regions near the base-collector junction. We have investigated the use of implanted Be and Mg, followed by rapid annealing at 700-900C to form high doped p layers, and multiple energy O implants (up to and including 1 MeV) to isolate the heterostructures. Annealing of implanted Be at >= 800C even at a dose of 2 x 10 sup 15 cm sup -2 results in complete activation whereas Mg shows only 30% activation under these conditions. There is no significant interface disordering visible by TEM or RBS for either case, and the use of rapid annealing severely restricts the redistribution of the implanted ions. The O bombarded layers show resistivities of 10 sup 8 OMEGA/square after 525C annealing.