The hole concentrations and lattice mismatch with the GaAs substrate of heavily carbon-doped epilayers (4.7×1019 and 9.8×1019 cm−3) were increased and the mobilities were decreased as compared with the as-grown samples by rapid thermal annealing silicon nitride capped samples at temperatures from 500 to 900 °C. However, for the more heavily doped sample, the hole concentration, mobility, and lattice mismatch decreased with increasing annealing temperature for annealing temperatures higher than 700 °C, but the hole concentration and lattice mismatch were still larger than those of the as-grown samples. Secondary ion mass spectroscopy results showed that annealing produced no change in the C concentration or distribution, but the hydrogen concentration decreased. Cross-sectional transmission electron microscopy indicated that no mismatch dislocations formed at the interface.

The formation of low temperature Au-Ge contacts to n-GaAs is a two-step process. In the first step, the metals segregate into Au and Ge rich regions and the intermixing of the Au and Ge with the Ga and As causes a reduction in the barrier height. The second step occurs after extended annealing, during which time Au and Ge continue to diffuse into the substrate. An orthorhombic Au-Ga phase is formed and it is likely that other Au-Ga or Ge-As phases are formed. The length of the extended anneal is dependent upon the atomic percent of Ge in the film, with the 10 at. % Ge taking 6 hr., the 27 at. % Ge taking 3 hr. and the 50 at. % Ge taking 9 hr. to become ohmic. The 75 at. % Ge sample doesn’t show ohmic behavior even after 33 hr. of annealing. The metal-semiconductor interface configuration appears abrupt, showing no protrusions into the GaAs substrate.

A thermally stable Pd/Ge/Ti/Pt/ ohmic contact with low specific contact resistance was formed on both n and p+-GaAs. The lowest specific contact resistances were 4.7×10−7 and 6.4×10−7 Ω.cm2 for the n and p+-GaAs, respectively, when the n-GaAs was doped with Si to 2×1018cm−3, and the p+-GaAs was doped with carbon to 5×1019 cm−3. Interfacial reactions and element diffusions of the contacts were investigated by using transmission electron microscopy, Auger electron spectrometry with depth profiles. All the contacts were thermally stable at 300 °C for 20 hours, and it appeared that the p-contacts were more stable than the n-contacts.