Recent advances in the technology and understanding of ohmic contacts to GaAs are presented. The paper emphasizes the reactions at the metal/GaAs interface and the structural factors which govern its electrical behavior and long-term stability. Results on the optimization of conventional gold-based ohmic contacts together with recent achievements in the technology of non-alloyed.contacts are overviewed.PACS numbers: 73.40Ns
Criteria for a good ohmic contactModern device concepts strongly depend on reliable and well-controlled electrical contacts through which one has to communicate with the interior of the device from the outside world. In particular, micron and submicron size Ill-V devices can be fully exploited only with adequate ohmic contacts. In addition to a wide variety of device and circuit applications, good quality ohmic contacts are required for investigating the physical and electrical properties of bulk materials and related III-V heterostructures. Consequently, much attention has been recently devoted to the development of ohmic contacts to III-V materials, and the research area include both, the fundamental behavior of metal/semiconductor contacts and the new techniques for improving the properties of ohmic contacts [1][2][3][4][5][6][7].The purpose of this paper is to bring together much of the fundamental and practical knowledge on the formation of ohmic contacts to GaAs. First, we give brief overview of the requirements for ohmic contacts in modern GaAs devices. Next, we shall comment on the actual state of understanding of the formation of potential barriers developing at metal/GaAs interfaces. While the detailed discussion of theories of metal/GaAs interface is beyond the scope of this article, basic concepts applicable to fabricate low-resistance contacts will be provided. The main part of the paper is devoted to up-todate approaches in the fabrication of ohmic contacts. We shall emphasize the reactions at the metal/semiconductor interface and the stuctural factors which govern its electrical behavior and long-term stability. Key technological issues of advanced contact technology will be given in Sec. 4.The main constraint on the choice of material for an ohmic contact is to ensure that it has the correct electrical properties. They are characterized by the (491)