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

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.