Development of ohmic contact materials for GaAs integrated circuits

GaAs is a very attractive material for special devices such as high-frequency microwave and optoelectronic devices which perform functions unattainable by Si devices. GaAs digital integrated circuits can operate at speeds beyond the capability of Si devices. In addition, compared with Si devices, the GaAs devices operate at lower power, are more radiation tolerant, and the device fabrication process is simpler. Two distinct types of contacts are fundamental components for GaAs devices: Ohmic (low-resistance) and Schottky (rectifying) type contacts. Performance of GaAs devices is strongly influenced by the electrical properties of these contacts. A variety of metallization systems for these contacts has been developed which provide promising device performance. With increase of the integration level of devices, thermal stability during device fabrication process and operation, control of the diffusion depth of the contact metals into the GaAs, and smooth surface morphology have become important issues as well as the electrical properties. The purpose of the present article is to review the development of Ohmic contact materials for GaAs devices prepared by conventional evaporation and annealing techniques and to discuss compatibility of these contact materials with highly integrated circuits.