Thermally stable ohmic contacts to p-type GaAs. IX. NiInW and NiIn(Mn)W contact metals

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Abstract
Thermally stable, low‐resistance p‐type ohmic contacts have been developed by depositing NiInW metals on GaAs substrates in which Be and F were coimplanted. The contacts provided resistances of about 1.4 Ω mm after annealing at temperatures in the range of 300–800 °C for short times. The electrical properties did not deteriorate after annealing at 400 °C for more than 100 h, which far exceeds the requirements for current GaAs device fabrication. The present study demonstrated for the first time that thermally stable, low‐resistance ohmic contacts to both n‐ and p‐type GaAs can be fabricated using the same metallurgy. In addition, NiInW ohmic contacts were prepared by simultaneous (one‐step) annealing for ion‐implant activation and contact formation, which simplifies significantly the device fabrication process. A factor‐of‐2 reduction of the contact resistances was achieved by slight etching of the GaAs surface prior to the contact metal deposition so that the metal/GaAs interface contacted the peak position of the Be concentration in the GaAs substrate. Another method used to reduce the contact resistance was to add a small amount of Mn to the NiInW metals: the resistance decreased with increasing amounts of Mn. The contacts had smooth morphology and shallow depth, less than 70 nm, which is desirable for very‐large‐scale integration device application.