A CLOSED UHV FOCUSED ION-BEAM PATTERNING AND MBE REGROWTH TECHNIQUE

An in situ ultra-high vacuum processing technique using a direct-write focused ion beam (FIB) implantation in combination with an epitaxial regrowth by molecular beam epitaxy (MBE) is reported. The process is s uitable for the realization of buried confinement structures and curre nt blocking layers in novel devices. By using a Ga+ FIB process highly conducting n(+)-GaAs (38 Omega/square) layers are converted into high ly resistive regions (10(8) Omega/square), which are thermally stable up to temperatures above 500 degrees C. The ion depth distribution is investigated by photoluminescence (PL) measurements on InGaAs-GaAs mul tiple-quantum-well samples. Owing to channeling effects the penetratio n depth is drastically enhanced. Excellent regrown GaAs-InGaAs-AlGaAs MODFET layers on FIB implanted wafers are fabricated and characterized by variable-field Hall and PL measurements. 300 K two-dimensional ele ctron gas mobilities of 6500 cm(2) V-1 s(-1) and carrier densities of 1.7 x 10(12) cm(-2) are achieved both on FIB implanted and non-implant ed regions. These values are comparable with conventionally grown refe rence samples. Lateral ion straggling and depletion zone effects are i nvestigated on planar resonant tunnelling diodes (RTDs) defined by FIB implantation. Sub-micrometer current path RTDs with a 300 K peak-to-v alley current ratio above 6 are fabricated. Lateral FIB dose-dependent depletion zone effects significantly reduce the effective electrical width of the current channel.