Ohmic Contacts to GaAs: Fundamentals and Practice

Abstract

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)

Comparison of Ti/Pd/Ag, Pd/Ti/Pd/Ag and Pd/Ge/Ti/Pd/Ag contacts to n-type GaAs for electronic devices handling high current densities

“…In such devices, the minimization of ohmic losses needs to be addressed not only at the semiconductor-metal interface, but also in the top metal layer itself where large current densities flow laterally. Therefore, the search for metallization systems with low contact resistance, high metal sheet conductivity, good bondability, reliability and cost-effectiveness continue to be an interesting and longstanding research topic [6][7][8][9][10]. For ohmic contacts on GaAs, the AuGe/Ni/Au contact has been extensively used for several decades since its inception in 1967 [11][12][13] due to its low contact resistance and good adherence caused by the alloying process with controllable roughness [14].…”

ABOUT AlGaAs-HETEROSTRUCTURES CVC KINETICS SIMULATION

“…For the validation of the presented model, the current-voltage characteristics of a number of RTS were calculated taking into account diffusion changes at the technological stage of annealing the structure for 30 s at 800°C [15][16][17][18][19]. The simulation was carried out self-consistently with regard to dissipative processes (the number of self-consistency iterations is 20, the inter-valley interaction constant is 0.7 eV Å, the optical potential in the quantum well is 0.02 eV).…”

“…To estimate the effect of structure degradation, technological annealing of a resonant tunneling structure (RTS) was simulated at a temperature of 800°C [14][15][16][17]. The duration of annealing is 30 s, but in order to make the calculation results more distinguishable, the simulated annealing time is increased 4 times.…”

Performance characteristics of a Labetalol‐H plus‐tetraphenylborate selective electrode

“…Due to its combined activity the drug is useful in treating hypertensive emergencies [ 11. A number of methods were suggested for the determination of secondary amino drugs, such as amperometry [2], ultraviolet (W) spectrometry [2], TLC [3], HPLC [4], liquid chromatography (51, direct or indirect titrations [6], direct potentiometry using coated-wire ion selective electrodes [? -9], or PVC membrane electrodes [lo].…”