ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Elemental diffusion, interfacial microstructure, and phase composition of Pt/Ti/Ge/Pd ohmic contacts to heavily C-doped Al0.26Ga0.74As were investigated at several annealing temperatures. Results of the material analyses were used to explain the previously determined specific contact resistances measured for each thermal treatment. Evidence of interdiffusion and compound formation between AlGaAs and Pd were visible in a Ga rich Pd-Ga-As reaction zone prior to heat treatment. This phase is critical for the formation of Ga vacancies, which upon heating are occupied by in-diffusing Ge. However, as the annealing temperatures are raised to 530 °C and above, As preferentially out diffuses. The As out diffusion, which is critical to the formation of good p-type ohmic contacts by creating vacancies that the amphoteric Ge can occupy, contributed to the creation and development of the two phase TiAs/Pd12Ga2Ge5 interfacial region overlying the AlGaAs substrate. In response to the enhanced As out diffusion at 600 °C, the interfacial region reached completion, that is, it became laterally continuous and compositionally uniform, and the specific contact resistance achieved its minimum value. At higher annealing temperatures ∼650 °C, the electrical measurements degraded in response to intensive chemical diffusion which resulted in the development of a broad, nonuniform multiphased interfacial region, and the Pt contacting layer ceased to be a homogeneous layer with a smooth surface. The As interfacial compounds form at higher temperatures in AlGaAs than in GaAs suggesting that As is more strongly bonded in the AlGaAs. This contributes to the greater temperature stability of the contacts to AlGaAs. © 1995 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.359272
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