Characterization of the n-GaAs/SnNi/Ni/Au ohmic contact

Analysis of the SnNi/Ni/Au ohmic contact to n-type GaAs is presented. Properties of high-quality ohmic contacts such as low specific contact resistance and current-voltage linearity are discussed with respect to the alloyed SnNi/Ni/Au ohmic contact. The effects of changing such processing parameters as alloying time and metal concentration and of including a Pt diffusion barrier are considered. An outline of techniques used to measure the specific contact resistance of ohmic contacts is presented. A comparison is made between two specific contact resistance determination techniques: the conventional transfer length method (TLM) and the more physically intuitive sandwich structure (which is used in this investigation). The analysis indicates that the TLM provides a convenient first-order approximation to the contact resistance, whereas the sandwich structure provides a more accurate value because the effects of current crowding along the periphery of the contact are eliminated