| 摘要 |
A group III nitride semiconductor device of field effect transistor type having improved productivity, reduced parasitic capacitances adapted for excellent device performance in high-speed operation as well as good heat diffusion characteristics. The device includes an epitaxial growth layer of a group III nitride semiconductor with a buffer layer laid under it, formed on an A plane (an (11-20) plane) of a sapphire. Thereon a gate electrode, a source electrode, a drain electrode, and pad electrodes are formed, and a ground conductor layer is formed on the back face of the sapphire substrate. A thickness of said sapphire substrate tsub satisfies the following Equation (1).whereSpad is an area of the pad electrode;Sgate is an area of the gate electrode;epsilonsub is a relative permittivity of the sapphire substrate in the direction of the thickness;epsilonepi is a relative permittivity of the group III nitride semiconductor layer in the direction of the thickness;tsub is a thickness of the sapphire substrate; andtact is an effective thickness of the group III nitride semiconductor layer.
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