The fabrication procedure for silicon carbide power metal oxide semiconductor field-effect transistors can be improved through simultaneous formation (i.e., using the same contact materials and a one-step annealing process) of ohmic contacts on both the n-source 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 min in an ultrahigh vacuum. Ohmic contacts to n-type SiC were found when the Al-layer thickness was less than about 6 nm, while ohmic contacts to p-type SiC were observed for an Al-layer thickness greater than about 5 nm. Only the contacts with an Al-layer thickness in the range of 5 nm to 6 nm exhibited ohmic behavior to both n-and p-type SiC, with a specific contact resistance of 1.8 9 10 -4 X cm 2 and 1.2 9 10 -2 X cm 2 for n-and p-type SiC, respectively. An about 100-nm-thick contact layer was uniformly formed on the SiC substrate, and polycrystalline d-Ni 2 Si(Al) grains were formed at the contact/SiC interface. In the samples that exhibited ohmic behavior to both n-and p-type SiC, the distribution of the Al/Ni ratios in the d-Ni 2 Si(Al) grains was larger than that observed for any of the samples that showed ohmic behavior to either n-or p-type SiC. Furthermore, the grain size of the d-Ni 2 Si(Al) grains in the samples showing ohmic behavior to both n-and p-type SiC was smaller than the grains in any of the samples that showed ohmic behavior to either n-or p-type SiC. 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. Grains with a low Al concentration correspond to ohmic contacts to n-type SiC, while grains with a high Al concentration correspond to ohmic contacts to p-type SiC.

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.

The electrical and optical properties, and microstructures of 100 nm-thick Ga2O3 films fabricated on Al2O3(0001) substrates by a sputtering deposition were investigated. The partial pressure of oxygen was controlled and the substrate temperature was kept to be 500 °C during deposition. With increasing the oxygen partial pressure, the structures of the Ga2O3 films deposited on the substrates were observed to change from amorphous to crystalline (monoclinic β-type Ga2O3). The transmittance of the Ga2O3 films was measured to be more than 80 % at the visible and ultraviolet regions although the electrical resistivity was high. In order to obtain both low electrical resistivity and high transmittance at the ultraviolet regions, the addition of active dopant elements such as Sn into the Ga2O3 films would be required.

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