Metal contacts to wide bandgap semiconductor structures for RF power applications

The increasing demand for electronic transistor with the cut-off frequency 100 GHz devices capable of function at high power and have been demonstrated this year. frequency levels, high temperatures, and harsh In order to take the full advantage of their environment is one of the most significant issue superior inherent properties several challenges of modern information society, especially in the in material processing are to be overcome. One field of RF systems for telecommunication and of the most important issue is the quality of wireless communication. Moreover, energy metal-semiconductor contacts. This is problems and environmental concerns due to especially true for both, for Schottky barriers global warming have generated the need for to be used in Schottky rectifiers and for ohmic novel semiconductor devices for active contacts being a part of any semiconductor electrical power management in areas such as device. The ohmic contacts are primarily energy generation and distribution, and important because a potential barrier of high transport where efficiency and/or high energy is inclined to form at an interface temperature operation are of the essence. Wide between metal and wide-band-gap bandgap semiconductor devices, particularly semiconductor, which consequently results in those using SiC and GaN-based materials, are low-current driving, slow switching speed, and key candidates for power-control and high- increased power dissipation. This paper speed communication devices, owing to their provides a comprehensive and critical excellent intrinsic properties, which involve assessment of fundamentals and practice of large breakdown electric field, in the 5×10⁶ metal contacts to wide bandgap Vcm^-1 range, together with high electron semiconductors with an emphasis on high saturation drift velocity, strong hardness, and power/temperature handling capability. The good thermal conductivity. GaN is already topics covered in this paper - - are grouped in five used in high-frequency circuits and is subsections. First, deals with carrier transport attracting increasing attention as a material to mechanisms in metal-semiconductor contacts, play a leading role in the next generation of which are applicable to any metal-power electronics. On the other hand, much semiconductor system. In the next section, effort have been already put in SiC technology points specific to metal/SiC and metal/GaN and first SiC power devices have already been contacts are discussed. Then, there is a place commercialised. Moreover, SiC is the favourite for a discussion of ohmic contacts, their substrate for GaN-based high-power and high- fabrication and characterisation methods. In frequency applications. SiC also appears as particular, the issue of determining properly enabling platform for large area graphene ohmic contact resistivity is discussed in detail. electronics, while a radio-frequency graphene The main part of the paper presents most significant results concerning thermally activated reactions between metal and properties of interface and its role in formation semiconductor and formation of intermediate of Schottky barriers and ohmic contacts. For layers in metal/SiC and metal/GaN contacts. GaN-based materials experimental results on For SiC, attention focuses on the effect of an the use of MAX phases for thermally stable intermediate graphite layer on electronic metallization systems receive major interest.