A contact metallization scheme of Ge/Pd(Zn), based on the solid-phase regrowth principle, has been developed for the formation of Ohmic contact on p-InP. Typical contact resistivities of low 10−4 to low 10−5 Ω cm2 can be obtained after annealing at temperatures higher than 400 °C. Cross-sectional transmission electron microscopy study confirmed the solid-phase regrowth process in the InP substrate. Precipitates of trapped materials during solid phase regrowth have also been observed. A solid phase regrowth model is proposed to rationalize the electrical and metallurgical properties. This solid phase regrowth process is expected to form low resistance Ohmic contact on other In-based compound semiconductors.

A low resistance Zn/Pd Ohmic contact scheme to p-InP based on solid phase reactions has been investigated. Contact resistivity in the mid-10−5 Ω cm−2 could be obtained for contacts with an atomic ratio of Zn to Pd of ∼1.5. In addition to the solid phase regrowth process, a Zn3P2/InP heterojunction is formed at the contact/semiconductor interface. The Ohmic contact formation mechanism is rationalized with the formation of Zn3P2/InP heterojunction.

Single-element contacts, Pd or Ni, on various p-InP substrates grown by liquid-encapsulation Czochralski (LEC) and by metal-organic chemical vapor deposition were investigated. Pd or Ni contacts on the substrates supplied by one certain manufacturer were found to be ohmic with a minimum contact resistivity of ∼5×10−5 Ω cm2 after annealing between 420 and 500 °C. However, ohmic behavior was not observed for these contacts on other substrates. Hall measurement, double-crystal x-ray diffractometry, and photoluminescence technique were used to evaluate the substrates. It was speculated that existence of intrinsic defects, such as P vacancies and other possible defects, in p-InP grown by LEC method may be responsible for the observed difference in ohmic behavior. A defect-assisted tunneling mechanism is proposed to account for the observed ohmic behavior of single-element contacts on certain p-InP substrates. This approach is potentially useful for making ohmic contacts to other compound semiconductors.