Simultaneous Formation of n- and p-Type Ohmic Contacts to 4H-SiC Using the Binary Ni/Al System

Abstract

Fabrication procedure for silicon carbide power metal oxide semiconductor field effect transistors can be improved through simultaneous formation of ohmic contacts on both the nsource and p-well regions. We have succeeded in the simultaneous formation of Ni/Al ohmic contacts to n-and p-type SiC after annealing at 1000°C for 5 mins in an ultra-high vacuum. Ohmic contacts to n-type SiC were found when Al-layer thickness was less than about 5 nm while ohmic contacts to p-type SiC were observed for an Al-layer thickness greater than about 5 nm. Only the contacts with Al-layer thicknesses in the range of 5 to 6 nm exhibited ohmic behavior to both n-and p-type SiC, with specific contact resistances of 1.8 × 10 -4 Ωcm 2 and 1.2 × 10 -2 Ωcm 2 for n-and p-type SiC, respectively. An about 100 nm-thick contact layer was uniformly formed on the SiC substrate and polycrystalline δ-Ni 2 Si(Al) grains were formed at the contact/SiC interface. The distribution in values for the Al/Ni ratio in the δ-Ni 2 Si(Al) grains which exhibited ohmic behavior to both n-and p-type SiC was the largest. The smallest average δ-Ni 2 Si(Al) grain size was also observed in these contacts. Thus, the large distribution in the Al/Ni ratios and a fine microstructure were found to be characteristic of the ohmic contacts to both n-and p-type SiC.

Magnetic flux coordinates for analytic high-beta tokamak equilibria with flow

“…The leading order of the entropy S in ( 16) is given by S 1 (ψ 1 ) = p 1 n −γ 0 . The derivation of the GS equations shown here can be applied for the two-fluid MHD with finite Larmor radius effects [17,18,19] where the full GS equations have not derived yet since the equations are complicated.…”

“…By these orderings, the fast magnetosonic wave is excluded while the slow magnetosonic wave characterized by the poloidal sound velocity is retained. The derivation of equlibrium equations was extended to the two-fluid MHD with finite Larmor radius effects [19,17,18]. An analytic solution for the reduced MHD equilibrium was found [20,21].…”

Equilibria of toroidal plasmas with toroidal and poloidal flow in high-beta reduced magnetohydrodynamic models

“…The system of fluid moment equations for collisionless, magnetized plasmas needs a closure condition to truncate higher-rank fluid moments. In the equilibrium model with flow comparable to the poloidal-sound velocity [4], the parallel heat fluxes, a third order fluid moment, are neglected for simplicity to obtain a closed set of equations with the isotropic, adiabatic pressures for ions and electrons, while they are ordered out in the model with flow comparable to the poloidal Alfvén velocity [3]. In [11], two-fluid equilibria with cold ions and anisotropic pressures for massless electrons are studied.…”

“…The MHD equations for equilibria with flow reduce to the so-called generalized Grad-Shafranov (GS) equation and the Bernoulli law in axisymmetric systems [1,2]. Recently, this MHD model for flowing equilibria has been extended to include the hot ion effects such as the ion gyroviscosity and other finite Larmor radius (FLR) effects that are relevant to fusion plasmas as well as two-fluid effects [3][4][5]. Those small-scale effects cannot be neglected at the sharp boundary of a well-confined region in magnetically confined plasmas where high-beta is achieved by shear-flow suppression of instability and turbulent transport, while the ion FLR terms had been neglected in previous models of two-fluid equilibria [6][7][8][9].…”

“…Such poloidal-sonic flow is of interest because a transition of equilibrium occurs between sub-and superpoloidal-sonic flow [17][18][19][20][21][22][23][24] and also because the poloidalsound velocity is smaller than other characteristic velocities like the sound, Alfvén and poloidal-Alfvén velocities in tokamak plasmas and, therefore, more accessible to flows in experiments. We introduce pressure anisotropy and the parallel heat fluxes that were not taken into account in our previous formulation [4]. By means of asymptotic expansions, we drive a reduced set of equilibrium equations for highbeta tokamaks.…”