The specific contact resistance of A u / G e / N i alloy contacts to G a A s for transferred electron devices has been measured. It is found that a shallow sulfur diffusion under the contact is effective in reducing the specific contact resistance by up to two orders of magnitude. This procedure is expected to improve the uniformity of threshold and bias voltages in integrated circuit configurations by making the contact resistance only 1-10% of the total device resistance.Because of the low doping found in GaAs transferred electron devices (TED's) for microwave applications, the contact resistance to the device is the major part of the total device resistance. A survey of the literature indicates that for a given doping level, the contact resistance can vary uP to two orders of magnitude as the processing parameters are varied (1-5). Significant variation can also occur across a wafer in a given run. This situation is allowable for discrete device configurations where postsorting is possible. In integrated circuit configurations, however, local variations are intolerable because threshold and bias voltages must be uniform from one device to the next in the same circuit. The purpose of this paper is to show that a shallow sulfur diffusion u n d e r the metallization pads can reduce the contact resistance to 1-10% of the total device resistance. The specific contact resistance is lowered by approximately two orders of magnitude over that measured on nondiffused samples.The metallurgical and electrical properties of alloyed A u -G e / N i films on n -t y p e GaAs are relatively well understood (1). Edwards, Hartman, and Torrens (2) have summarized specific contact resistance data of this and other contact alloys to GaAs through mid-1971. In general, their data show two order of magnitude variation in the specific contact resistance which ranges from a m e a n of 3 • 10 -3 ~-c m at a doping level of mid-1015/cm 8 to 10 -4 ~-c m at 1017/cm ~. Robinson (3) and Yu (4) have independently confirmed that by process optimization, the mean specific contact resistance can be lowered by up to one order of magnitude. For GaAs TED's doped from mid-1015/cm ~ to mid-1016/cm 3, the specific contact resistance values reported as well as those measured in our laboratories give a device contact resistance far greater than the intrinsic device resistance (typically 3000~). To lower the contact resistance to 1-10% of the total device resistance, a specific contact resistance of ~10 -5 ~-c m is required. The exact value depends on the specific device configuration. This value is two orders of magnitude lower than that reported, and hence can only be achieved by the formation of a shallow n-t-layer below the contact to give a doping level of mid-1017/cm 3 to mid-101S/cm ~.The samples used in this experiment were semiinsulating GaAs substrates on which 25 #m vapor phase epitaxy layers were grown. The typical doping range was mid-1015/cm 8 to mid-1016/cm 3 n -t y p e (Si). Ohmic contacts were formed by evaporation of a gold/ 12 weight perc...