Ohmic Contacts To

Abstract

In this chapter, the most significant results obtained in the last decade in the field of ohmic contacts to SiC are reviewed. First, the basic concepts related to the physics of ohmic contacts and to the contact resistance measurement techniques are briefly reported. Then, some aspects concerning the formation of low resistance (10~5-10~6 £2cm 2 ) ohmic contacts on n-type and for p-type SiC are discussed, focusing on Ni-based and Al/Tibased contacts. Examples of innovative applications on practical devices are also reported, as the simultaneous formation of ohmic contacts on n-and p-type SiC for vertical power MOS devices, obtained adding Al to a standard Ni contact, and a single-metal technology for ohmic and rectifying contacts in MESFETs, using Ti or Ni without post-deposition annealing.

Nanoscale transport properties at silicon carbide interfaces

“…The lower drain current observed when the channel was fabricated with an orientation perpendicular to the step bunching (i.e. along the [11][12][13][14][15][16][17][18][19][20] direction) was explained by the different interface roughness appearing to the carriers in the two directions. Several methods are adopted to reduce roughness, like the use of a graphite capping layer before annealing [108,109,110] or chemical-mechanical-polishing (CMP) after annealing [111].…”

“…The electronic transport across metal/SiC interfaces, i.e. both Ohmic and rectifying (Schottky) contacts, has been the subject of extensive scientific investigations in the last decade [10,13,14]. The main reasons are the need to achieve a very low contact resistance to reduce the passive contribution to device performances, and to attain an ideal and reliable behaviour in the forward and reverse characteristics of Schottky diodes.…”

“…Typical values of the specific contact resistance ρ c of Ni 2 Si contacts onto heavily doped n-type SiC reported in the literature range between 10 −5 and 10 −7 cm 2 . The mechanisms of current transport and Ohmic contact formation in the Ni 2 Si/SiC system have been widely discussed in some review papers [13,14]. According to the common interpretation, a high concentration of carbon vacancies at the silicide/SiC interface is generated upon annealing, acting as donors and increasing the net carrier concentration below the metal [70].…”

“…Because of the low Schottky barrier, Al-or Ti/Al-based alloyed contacts are commonly used as Ohmic contacts to p-type SiC, leading to values of specific contact resistance in the order of 10 −3 -10 −5 cm 2 [14]. However, from the experimental results reported on Ti-Al Ohmic contacts to p-type SiC, it is not clear whether the spiking due to intrusions of the annealed metal into SiC leads to an increase in the doping by Al in-diffusion or rather the intrusions themselves act as field emitters increasing the leakage current and leading to the formation of an Ohmic contact [14].…”

Microstructure and Transport Properties in Alloyed Ohmic Contacts to P-Type SiC and GaN for Power Devices Applications

“…Ohmic contacts to SiC and GaN have been widely investigated in the last years [3,4,5]. Common issue to these reports is the intrinsic difficulty to form good Ohmic contacts to p-type SiC and ptype GaN.…”