A semiconductor device includes a buffer layer, a channel layer, a barrier layer, and agate electrode over a substrate, the gate electrode being disposed in a first opening with agate insulating film in between, the first opening running up to the middle of the channel layer through the barrier layer. The concentration of two-dimensional electron gas in a first region on either side of a second opening that will have a channel is controlled to be lower than the concentration of two-dimensional electron gas in a second region between an end of the first region and a source or drain electrode. The concentration of the two-dimensional electron gas in the first region is thus decreased, thereby the conduction band-raising effect of polarization charge is prevented from being reduced. This prevents a decrease in threshold potential, and thus improves normally-off operability.

A semiconductor device includes a substrate; a first nitride semiconductor layer formed on the substrate, a second nitride semiconductor layer formed on the first nitride semiconductor layer and containing gallium element; and a third nitride semiconductor layer formed on the second nitride semiconductor layer and containing indium element, aluminum element, and gallium element, in which the composition ratio of the gallium element of the third nitride semiconductor layer is a proportion smaller than that of the second nitride semiconductor layer.

Hybrid high electron mobility field-effect transistors including inorganic channels and organic gate barrier layers are used in some applications for forming high resolution active matrix displays. Arrays of such high electron mobility field-effect transistors are electrically connected to thin film switching transistors and provide high drive currents for passive devices such as organic light emitting diodes. The organic gate barrier layers are operative to suppress both electron and hole transport between the inorganic channel layer and the gate electrodes of the high electron mobility field-effect transistors.

A normally-off compound semiconductor transistor includes a heterostructure body and a gate stack on the heterostructure body. The heterostructure body includes a source, a drain spaced apart from the source, and a channel for connecting the source and the drain. The channel includes a first two-dimensional charge carrier gas of a first polarity arising in the heterostructure body due to piezoelectric effects. The gate stack controls the channel in a region of the heterostructure body under the gate stack. The gate stack includes at least one III-nitride material which gives rise to a second two-dimensional charge carrier gas of a second polarity opposite the first polarity in the gate stack or in the heterostructure body under the gate stack due to piezoelectric effects. The second two-dimensional charge carrier gas counter-balances polarization charges in the first two-dimensional charge carrier gas so that the channel is disrupted under the gate stack.

Device architectures based on trapping and de-trapping holes or electrons and/or recombination of both types of carriers are obtained by carrier trapping either in near-interface deep ambipolar states or in quantum wells/dots, either serving as ambipolar traps in semiconductor layers or in gate dielectric/barrier layers. In either case, the potential barrier for trapping is small and retention is provided by carrier confinement in the deep trap states and/or quantum wells/dots. The device architectures are usable as three terminal or two terminal devices.

A multi-layer semiconductor structure is disclosed for use in III-Nitride semiconductor devices, including a channel layer, a band-offset layer having a wider bandgap than the channel layer, a spacer layer having a narrower bandgap than the band-offset layer, and a cap layer comprising at least two sublayers. Each sublayer is selectively etchable with respect to sublayers immediately below and above, each sublayer comprises a III-N material Al.sub.xIn.sub.yGa.sub.zN in which 0x1, 0y1, and 0z1, at least one sublayer has a non-zero Ga content, and a sublayer immediately above the spacer layer has a wider bandgap than the spacer layer. Also described are methods for fabricating such semiconductor structures, with gate and/or ohmic recesses formed by selectively removing adjacent layers or sublayers. The performance of resulting devices is improved, while providing design flexibility to reduce production cost and circuit footprint.

Apparatus and circuits including transistors with different threshold voltages and methods of fabricating the same are disclosed. In one example, a semiconductor structure is disclosed. The semiconductor structure includes: a substrate; an active layer that is formed over the substrate and comprises a plurality of active portions; a polarization modulation layer comprising a plurality of polarization modulation portions each of which is disposed on a corresponding one of the plurality of active portions; and a plurality of transistors each of which comprises a source region, a drain region, and a gate structure formed on a corresponding one of the plurality of polarization modulation portions. The transistors have at least three different threshold voltages.

Provided is a heterojunction structure device. The heterojunction structure device includes: a gate electrode disposed on a substrate; a ferroelectric layer disposed on the gate electrode and including a material having ferroelectric characteristics; a channel layer disposed on the ferroelectric layer and including a material having ferroelectric and semiconductor characteristics; and a source electrode and a drain electrode disposed on the channel layer while being spaced apart from each other.

A semiconductor device includes: a plurality of transistors on a substrate, each transistor of the plurality of transistors including a source region, a drain region, a gate structure, a polarization modulation portion, and a polarization layer. The polarization modulation portion of each of the plurality of transistors is on the polarization layer, the plurality of transistors includes a first transistor having a first threshold voltage that has a first fixed value, and the plurality of transistors includes a second transistor having a second threshold voltage that has a second fixed value different from the first fixed value.

A method for fabricating a high electron mobility transistor (HEMT) includes the steps of forming a buffer layer on a substrate, forming a barrier layer on the buffer layer, forming a p-type semiconductor layer on the barrier layer, forming a hole injection buffer layer (HIBL) on the p-type semiconductor layer, and forming a gate electrode on the HIBL.