A High electron mobility transistor (HEMT) includes a source electrode, a gate electrode, a drain electrode, a channel forming layer in which a two-dimensional electron gas (2DEG) channel is induced, and a channel supplying layer for inducing the 2DEG channel in the channel forming layer. The source electrode and the drain electrode are located on the channel supplying layer. A channel increase layer is between the channel supplying layer and the source and drain electrodes. A thickness of the channel supplying layer is less than about 15 nm.

A nitride semiconductor device including a substrate, a channel layer, a carbon-poor barrier layer having a recess, a carbon-rich barrier layer disposed over the recess and the carbon-poor barrier layer, and a gate electrode above the recess, wherein the carbon-poor and carbon-rich barrier layers have bandgaps larger than that of the channel layer, the upper surface of the carbon-rich barrier layer includes a first main surface including a source electrode and a drain electrode, and a bottom surface of a depression disposed along the recess, and side surfaces of the depression connecting the first main surface to the bottom surface of the depression, and among edges of the depression of the carbon-rich barrier layer which are boundaries between the first main surface and the side surfaces of the depression, the edge of the depression of the carbon-rich barrier layer closest to the drain electrode is covered with the gate electrode.

A field-effect transistor (a GaN-based HFET) includes a gate electrode, a gate electrode pad, a first wiring line connecting one end of the gate electrode and the gate electrode pad, a second wiring line connecting the other end of the gate electrode and the gate electrode pad, and a resistance element that is connected to the first wiring line and is capable of adjusting the impedance of the first wiring line.

The semiconductor device includes: a channel layer, a barrier layer, a first insulating film, and a second insulating film, each of which is formed above a substrate; a trench that penetrates the second insulating film, the first insulating film, and the barrier layer to reach the middle of the channel layer; and a gate electrode arranged in the trench and over the second insulating film via a gate insulating film. The bandgap of the second insulating film is smaller than that of the first insulating film, and the bandgap of the second insulating film is smaller than that of the gate insulating film GI. Accordingly, a charge (electron) can be accumulated in the second (upper) insulating film, thereby allowing the electric field strength at a corner of the trench to be improved. As a result, a channel is fully formed even at a corner of the trench, thereby allowing an ON-resistance to be reduced and an ON-current to be increased.

A semiconductor device includes a substrate, a first semiconductor layer formed over the substrate, a plurality of contact layers formed over portions of the first semiconductor layer, a second semiconductor layer formed over another portion of the first semiconductor layer and on side surfaces of the contact layers, a source electrode formed on one of the contact layers, a drain electrode formed on another one of the contact layers, and a gate electrode formed on the second semiconductor layer. The first semiconductor layer is formed of a material including GaN, the second semiconductor layer is formed of In.sub.x1Al.sub.y1Ga.sub.1-x1-y1N (0<x10.2, 0<y1<1), and the contact layers are formed of a material including GaN.

A nitride semiconductor epitaxial wafer includes a substrate, a GaN layer provided over the substrate, and an AlGaN layer provided over the GaN layer. The GaN layer has a wurtzite crystal structure, and a ratio c/a of a lattice constant c in a c-axis orientation of the GaN layer to a lattice constant a in an a-axis orientation of the GaN layer is not more than 1.6266.

A high-electron-mobility semiconductor device includes: a buffer region having first, second and third cross-sections forming a stepped lateral profile, the first cross-section being thicker than the third cross-section and comprising a first buried field plate disposed therein, the second cross-section interposed between the first and third cross-sections and forming oblique angles with the first and third cross-sections; and a barrier region of substantially uniform thickness extending along the stepped lateral profile of the buffer region, the barrier region being separated from the first buried field plate by a portion of the buffer region. The buffer region is formed by a first semiconductor material and the barrier region is formed by a second semiconductor material. The first and second semiconductor materials have different band-gaps such that an electrically conductive channel including a two-dimensional charge carrier gas arises at an interface between the buffer and barrier regions due to piezoelectric effects.

A method of forming a compound semiconductor substrate includes providing a crystalline base substrate having a first semiconductor material and a main surface, and forming a first semiconductor layer on the main surface and having a pair of tracks disposed on either side of active device regions. The first semiconductor layer is formed from a second semiconductor material having a different coefficient of thermal expansion than the first semiconductor material. The pair of tracks have a relatively weaker crystalline structure than the active device regions. The method further includes thermally cycling the base substrate and the first semiconductor layer such that the first semiconductor layer expands and contracts at a different rate than the base substrate. The pair of tracks physically decouple adjacent ones of the active device regions during the thermal cycling.

In an embodiment, a semiconductor device includes a Group III-nitride-based High Electron Mobility Transistor (HEMT) configured as a bidirectional switch. The Group III nitride-based HEMT includes a first input/output electrode, a second input/output electrode, a gate structure arranged between the first input/output electrode and the second input/output electrode, and a field plate structure.

In order to improve the characteristics of a semiconductor device including: a channel layer and a barrier layer formed above a substrate; and a gate electrode arranged over the barrier layer via a gate insulating film, the semiconductor device is configured as follows. A silicon nitride film is provided over the barrier layer between a source electrode and the gate electrode, and is also provided over the barrier layer between a drain electrode and the gate electrode GE. The surface potential of the barrier layer is reduced by the silicon nitride film, thereby allowing two-dimensional electron gas to be formed. Thus, by selectively forming two-dimensional electron gas only in a region where the silicon nitride film is formed, a normally-off operation can be performed even if a trench gate structure is not adopted.