A method for fabricating a double-recess gate structure for an FET device that includes providing a semiconductor wafer having a plurality of semiconductor layers and depositing an EBL resist layer on the wafer. The method also includes patterning the EBL resist layer to form an opening in the EBL resist layer and performing a first wet etch to form a first recess in the wafer. The method further includes depositing a dielectric layer over the EBL resist layer and into the first recess and performing a dry etch to remove a portion of the dielectric layer in the first recess. The method also includes performing a second wet etch through the opening in the dielectric layer to form a second recess, and depositing a gate metal layer in the first and second recesses and in the opening in the EBL resist layer to form a gate terminal.

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 field effect transistor (FET) device including a substrate and a plurality of semiconductor layers provided on the substrate, where a top semiconductor layer is a heavily doped cap layer and another one of the semiconductor layers directly below the cap layer is a Schottky barrier layer, and where a gate recess is formed through the cap layer and into the Schottky barrier layer. The FET device also includes a gate terminal having a titanium layer, an inhibitor layer provided on the titanium layer and a gold layer provided on the inhibitor layer, where the gate terminal is formed in the recess so that the titanium layer is in contact with the Schottky barrier layer, and where the inhibitor layer is effective for preventing hydrogen gas from being dissociated into hydrogen atoms so as to reduce or prevent hydrogen poisoning of the FET device.

A compound semiconductor device includes: a substrate; and a buffer layer, a first carrier supply layer, a first spacer layer, a channel layer, a second spacer layer, a second carrier supply layer, and a contact layer provided in order on the substrate, wherein the first carrier supply layer is a uniformly doped layer in which an impurity is uniformly doped, the second carrier supply layer is a planar doped layer in which an impurity is locally doped, and no Al mixed crystal layer having higher resistance values than the first and second spacer layers is provided between the buffer layer and the first spacer layer and between the second spacer layer and the contact layer.

A semiconductor wafer includes a base wafer, a first semiconductor portion that is formed on the base wafer and includes a first channel layer containing a majority carrier of a first conductivity type, a separation layer that is formed over the first semiconductor portion and contains an impurity to create an impurity level deeper than the impurity level of the first semiconductor portion, and a second semiconductor portion that is formed over the separation layer and includes a second channel layer containing a majority carrier of a second conductivity type opposite to the first conductivity type.

Provided is a semiconductor device that includes a drain electrode and a source electrode, a gate electrode, one or more gate-electrode extensions, and a link. The drain electrode and the source electrode have a planar shape of combs in mesh with each other. The gate electrode is provided between the drain electrode and the source electrode, and has a meandering planar shape. The one or more gate-electrode extensions are projected from the gate electrode. The link is confronted with one or both of the drain electrode and the source electrode, and couples the one or more gate-electrode extensions together.

An epitaxial structure for a high-electron-mobility transistor includes a substrate, a nucleation layer, a buffer layered unit, a channel layer, and a barrier layer sequentially stacked on one another in such order. The buffer layered unit includes a plurality of p-i-n heterojunction stacks. Each of the p-i-n heterojunction stacks includes p-type, i-type, and n-type layers which are made of materials respectively represented by chemical formulas of Al.sub.xGa.sub.(1-x)N, Al.sub.yGa.sub.(1-y)N, and Al.sub.zGa.sub.(1-z)N. For each of the p-i-n heterojunction stacks, x decreases and z increases along a direction away from the nucleation layer, and y is consistent and ranges from 0 to 0.7.

One or more semiconductor structures comprising a hole draining structure are provided. A semiconductor structure has a first layer formed over a substrate. The first layer has a first concentration of a metal material. The semiconductor structure has a second layer formed over the first layer. The second layer has a second concentration of the metal material different than the first concentration of the metal material. The semiconductor structure has a hole draining structure formed from a superlattice formed between the first layer and the second layer. The hole draining structure has a concentration of the metal material increasing towards the first layer and decreasing towards the second layer.

In one embodiment, a transistor includes a substrate, a buffer layer on the substrate a channel layer on the buffer layer, and one or more polarization layers on the channel layer. The one or more polarization layers include a group III-N material comprising a first group III constituent and a second group III constituent. The transistor further includes a plurality of p-type doped layers on the one or more polarization layers. Each of the plurality of p-type doped layers includes a first p-type dopant and the III-N material, wherein each successive layer of the first p-type doped layers has a lower proportion of the first group III constituent to the second group III constituent relative to a layer below it. The transistor also includes a p-type doped layer on the plurality of p-type doped layers comprising a second p-type dopant and a group III-N material.

According to one embodiment, a nitride semiconductor includes a nitride member. The nitride member includes a first nitride region including Al.sub.x1Ga.sub.1-x1N, a second nitride region including Al.sub.x2Ga.sub.1-x2N, and a third nitride region including Al.sub.x3Ga.sub.1-x3N. The second nitride region is provided between the first and third nitride regions in a first direction from the first nitride region to the second nitride region. The second nitride region includes carbon and oxygen. The first nitride region does not include carbon, or a second carbon concentration in the second nitride region is higher than a first carbon concentration in the first nitride region. The second carbon concentration is higher than a third carbon concentration in the third nitride region. A ratio of a second oxygen concentration in the second nitride region to the second carbon concentration is not less than 1.010.sup.4 and not more than 1.410.sup.3.