Ion beam synthesis and n-type doping of group III–Nx–V1−x alloys

Abstract

Investigations on the synthesis of group III–Nx–V1−x alloy including GaNxAs1−x, InNxP1−x and AlyGa1−yNxAs1−x using N ion implantation followed by rapid thermal annealing are reviewed. The fundamental band-gap energy for the ion beam synthesized III–Nx–V1−x alloys is found to decrease with increasing N-implantation dose and can be quantitatively described by the anticrossing interaction between the localized N-states and the extended states of the semiconductor matrix. N activation efficiencies in these N ion synthesized alloy films are found to be low, ∼10% for GaNxAs1−x and ∼20% for InNxP1−x. A preliminary study showed that using pulsed laser melting followed by rapid thermal annealing greatly enhanced the N activation efficiency (∼50%) in N-implanted GaAs. The N-induced conduction band modification also results in an enhancement of the maximum free electron concentration in GaNxAs1−x. A maximum free electron concentration as high as 7 × 1019 cm−3 was observed in heavily Se-doped Ga1−3xIn3xNxAs1−x (x = 0.033) films, more than 20 times larger than that observed in GaAs films grown under similar conditions. A similar increase in free electron concentration was also achieved in a S-implanted GaNxAs1−x thin film. Combining the ion synthesis of diluted nitrides and S implantation doping techniques, we realized a large increase in the electrical activation of S co-implanted with N in GaAs within a thin near-surface region (∼500 Å), indicating the formation of a heavily doped thin diluted GaNxAs1−x alloy layer with x ∼ 0.3%. This result has important practical implications on the fabrication of low-resistance, non-alloyed ohmic contacts to n-type GaAs.