The formation of low resistance electrical contacts to shallow junction InP devices without compromising emitter integrity

Abstract

An investigation is made into the possibility of providing low resistance contacts to shallow junction InP devices which do not require sintering and which do not cause device degradation even when subjected to extended annealing at elevated temperatures. We show that the addition of In to Au contacts in amounts that exceed the solid solubility limit lowers the as-fabricated (unsintered) contact resistivityR _c to the 10^-5 ohm-cm² range. If the In content is made to correspond exactly to that required to form the intermediate compound Au₉ln₄, then the contacts so formed are stable, both electrically and metallurgically, even after extended annealing (12 hr) at 400° C. We next consider the contact system Au/Au₂P₃ which has been shown to exhibit as-fabricatedR _c values in the 10^-6 ohm-cm² range, but which fails quickly when heated. We show that the substitution of a refractory metal (W, Ta) for Au preserves the lowR _c values while preventing the destructive reactions that would normally take place in this system at high temperatures. We show, finally, thatR _c values in the 10 ohm-cm² range can be achievedwithout sintering by combining the effects of In or Ga additions to Au contacts with the effects of introducing a thin Au₂P₃ layer at the metal-InP interface.