Abstract: A structure for radiofrequency applications includes a high-resistivity support substrate having a front face defining a main plane, a charge-trapping layer disposed on the front face of the support substrate, a first dielectric layer disposed on the charge-trapping layer, an active layer disposed on the first dielectric layer, at least one buried electrode disposed above or in the charge-trapping layer. The buried electrode comprises a conductive layer and a second dielectric layer.

Abstract: High electron mobility transistors (HEMTs) and methods of manufacturing the same. A HEMT may include a source electrode, a gate electrode, a drain electrode, a channel formation layer including at least a 2-dimensional electron gas (2DEG) channel, a channel supplying layer for forming the 2DEG channel in the channel formation layer, a portion of the channel supplying layer including a first oxygen treated region. The channel supplying layer may include a second oxygen treated region that extends from the first oxygen treated region towards the drain electrode, and the depth and concentration of oxygen of the second oxygen treated region may be less than those of the first oxygen treated region.

Abstract: An HEMT includes, on an SiC substrate, a compound semiconductor layer, a silicon nitride (SiN) protective film having an opening and covering the compound semiconductor layer, and a gate electrode formed on the compound semiconductor layer so as to plug the opening. In the protective film, a projecting portion projecting from a side surface of the opening is formed at a lower layer portion 6a.

Abstract: An electrode structure, a GaN-based semiconductor device including the electrode structure, and methods of manufacturing the same, may include a GaN-based semiconductor layer and an electrode structure on the GaN-based semiconductor layer. The electrode structure may include an electrode element including a conductive material and a diffusion layer between the electrode element and the GaN-based semiconductor layer. The diffusion layer may include a material which is an n-type dopant with respect to the GaN-based semiconductor layer, and the diffusion layer may contact the GaN-based semiconductor layer. A region of the GaN-based semiconductor layer contacting the diffusion layer may be doped with the n-type dopant. The material of the diffusion layer may comprise a Group 4 element.

Abstract: A graphene capped HEMT device and a method of fabricating same are disclosed. The graphene capped HEMT device includes one or more graphene caps that enhance device performance and/or reliability of an exemplary AlGaN/GaN heterostructure transistor used in high-frequency, high-energy applications, e.g., wireless telecommunications. The HEMT device disclosed makes use of the extraordinary material properties of graphene. One of the graphene caps acts as a heat sink underneath the transistor, while the other graphene cap stabilizes the source, drain, and gate regions of the transistor to prevent cracking during high-power operation. A process flow is disclosed for replacing a three-layer film stack, previously used to prevent cracking, with a one-atom thick layer of graphene, without otherwise degrading device performance. In addition, the HEMT device disclosed includes a hexagonal boron nitride adhesion layer to facilitate deposition of the compound nitride semiconductors onto the graphene.

Abstract: A method of manufacturing a semiconductor device includes laminating and forming an electron transit layer, an electron supplying layer, an etching stop layer, and a p-type film on a substrate sequentially, the p-type film being formed of a nitride semiconductor material that includes Al doped with an impurity element that attains p-type, the etching stop layer being formed of a material that includes GaN, removing the p-type film in an area except an area where a gate electrode is to be formed, by dry etching to form a p-type layer in the area where the gate electrode is to be formed, the dry etching being conducted while plasma emission in the dry etching is observed, the dry etching being stopped after the dry etching is started and plasma emission originating from Al is not observed, and forming the gate electrode on the p-type layer.

Abstract: A device includes a source and a drain for transmitting and receiving an electronic charge. The device also includes a first stack and a second stack for providing at least part of a conduction path between the source and the drain, wherein the first stack includes a first gallium nitride (GaN) layer of a first polarity, and the second stack includes a second gallium nitride (GaN) layer of the second polarity, and wherein the first polarity is different from the second polarity. At least one gate operatively connected to at least the first stack for controlling a conduction of the electronic charge, such that, during an operation of the device, the conduction path includes a first two-dimensional electron gas (2DEG) channel formed in the first GaN layer and a second 2DEG channel formed in the second GaN layer.

Abstract: There are disclosed herein various implementations of a semiconductor structure and method. The semiconductor structure comprises a substrate, a transition body over the substrate, and a group III-V intermediate body having a bottom surface over the transition body. The semiconductor structure also includes a group III-V device layer over a top surface of the group III-V intermediate body. The group III-V intermediate body has a continuously reduced impurity concentration wherein a higher impurity concentration at the bottom surface is continuously reduced to a lower impurity concentration at the top surface.

Abstract: A circuit structure includes a substrate, a nucleation layer of undoped aluminum nitride, a graded buffer layer comprising aluminum, gallium, nitrogen, one of silicon and oxygen, and a p-type conductivity dopant, a ungraded buffer layer comprising gallium, nitrogen, one of silicon and oxygen, and a p-type conductivity dopant without aluminum, and a bulk layer of undoped gallium nitride over the ungraded buffer layer. The various dopants in the graded buffer layer and the ungraded buffer layer increases resistivity and results in layers having an intrinsically balanced conductivity.

Abstract: A semiconductor device, comprising: a substrate; a plurality of gate finger electrodes which are arranged on the substrate; a plurality of source finger electrodes which are arranged on the substrate, each source finger electrode is close to the gate finger electrode; a plurality of drain finger electrodes which are arranged on the substrate, each drain finger electrode faces the source finger electrode via the gate finger electrode; a shield plate electrode which is arranged via an insulating layer over the drain finger electrode and the first surface of the substrate between the gate finger electrode and the drain finger electrode, is short-circuited to the source finger electrode, and shields electrically the gate finger electrode and the drain finger electrode from each other; and a slot VIA hole which is formed in the substrate under the source finger electrode and is connected to the source finger electrode.

Abstract: A semiconductor device includes a Si substrate having a principal plane that is a crystal surface inclined at an off angle of 0.1 degrees or less with respect to a (111) plane, an AlN layer that is provided so as to contact the principal plane of the Si substrate and is configured so that an FWHM of a rocking curve of a (002) plane by x-ray diffraction is not greater than 2000 seconds, and a GaN-based semiconductor layer formed on the AlN layer.

Abstract: A III-N device is described has a buffer layer, a first III-N material layer on the buffer layer, a second III-N material layer on the first III-N material layer on an opposite side from the buffer layer and a dispersion blocking layer between the buffer layer and the channel layer. The first III-N material layer is a channel layer and a compositional difference between the first III-N material layer and the second III-N material layer induces a 2DEG channel in the first III-N material layer. A sheet or a distribution of negative charge at an interface of the channel layer and the dispersion blocking layer confines electrons away from the buffer layer.

Abstract: Compression strains are generated at an interface between the cap layer and the barrier layer and an interface between the channel layer and the buffer layer and a tensile strain is generated at an interface between the barrier layer and the channel layer. Therefore, negative charge is higher than positive charge at the interface between the cap layer and the barrier layer and the interface between the channel layer and the buffer layer, while positive charge is higher than negative charge at the interface between the barrier layer and the channel. The channel layer has a stacked layer structure of a first layer, a second layer, and a third layer. The second layer has a higher electron affinity than those of the first layer and the third layer.

Abstract: Enhancement mode III-nitride devices are described. The 2DEG is depleted in the gate region so that the device is unable to conduct current when no bias is applied at the gate. Both gallium face and nitride face devices formed as enhancement mode devices.

Abstract: A hetero-junction tunneling transistor having a first layer of p++ silicon germanium which forms a source for the transistor at one end. A second layer of n+ silicon material is deposited so that a portion of the second layer overlies the first layer and forms the drain for the transistor. An insulating layer and metallic gate for the transistor is deposited on top of the second layer so that the gate is aligned with the overlying portions of the first and second layers. The gate voltage controls the conduction between the source and the drain and the conduction between the first and second layers occurs by vertical tunneling between the layers.

Abstract: An embodiment of a compound semiconductor device includes: a substrate; an electron channel layer and an electron supply layer formed over the substrate; a gate electrode, a source electrode and a drain electrode formed on or above the electron supply layer; and a p-type semiconductor layer formed between the electron supply layer and the gate electrode. The p-type semiconductor layer contains, as a p-type impurity, an element same as that being contained in at least either of the electron channel layer and the electron supply layer.

Abstract: Disclosed herein are embodiments of a normally-off compound semiconductor tunnel field effect transistor having a drive current above 100 mA per mm of gate length and a sub-threshold slope below 60 mV per decade at room temperature, and methods of manufacturing such a normally-off compound semiconductor tunnel transistor. The compound semiconductor tunnel field effect transistor is fast-switching and can be used for high voltage applications e.g. 30V up to 600V and higher.

Abstract: An integrated optical waveguide has a first optical waveguide, a second optical waveguide, and a groove. The second optical waveguide is coupled to the first optical waveguide and has a refractive index that is different from the first optical waveguide. The groove is disposed so as to traverse an optical path of the first optical waveguide and is separated from an interface between the first optical waveguide and the second optical waveguide by a predetermined spacing. The spacing from the interface and the width of the groove are determined such that reflection at a boundary between the first optical waveguide and the second optical waveguide is weakened. A semiconductor board may be disposed at a boundary between the first optical waveguide and the second optical waveguide.

Abstract: Provided is a nitride semiconductor device including: a nitride semiconductor layer over a substrate wherein the nitride semiconductor has a two-dimensional electron gas (2DEG) channel inside; a drain electrode in ohmic contact with the nitride semiconductor layer; a source electrode spaced apart from the drain electrode, in Schottky contact with the nitride semiconductor layer, and having an ohmic pattern in ohmic contact with the nitride semiconductor layer inside; a dielectric layer formed on the nitride semiconductor layer between the drain electrode and the source electrode and on at least a portion of the source electrode; and a gate electrode disposed on the dielectric layer to be spaced apart from the drain electrode, wherein a portion of the gate electrode is formed over a drain-side edge portion of the source electrode with the dielectric layer interposed therebetween, and a manufacturing method thereof.

Abstract: An enhancement mode III-Nitride device has a floating gate spaced from a drain electrode which is programmed by charges injected into the floating gate to form a permanent depletion region which interrupts the 2-DEG layer beneath the floating gate. A conventional gate is formed atop the floating gate and is insulated therefrom by a further dielectric layer. The device is a normally off E mode device and is turned on by applying a positive voltage to the floating gate to modify the depletion layer and reinstate the 2-DEG layer. The device is formed by conventional semiconductor fabrication techniques.

Abstract: Enhancement mode III-nitride devices are described. The 2DEG is depleted in the gate region so that the device is unable to conduct current when no bias is applied at the gate. Both gallium face and nitride face devices formed as enhancement mode devices.

Abstract: An AlN layer (2), a GaN buffer layer (3), a non-doped AlGaN layer (4a), an n-type AlGaN layer (4b), an n-type GaN layer (5), a non-doped AlN layer (6) and an SiN layer (7) are sequentially formed on an SiC substrate (1). At least three openings are formed in the non-doped AlN layer (6) and the SiN layer (7), and a source electrode (8a), a drain electrode (8b) and a gate electrode (19) are evaporated in these openings.

Abstract: Semiconductor heterostructures to reduce short channel effects are generally described. In one example, an apparatus includes a semiconductor substrate, one or more buffer layers coupled to the semiconductor substrate, a first barrier layer coupled to the one or more buffer layers, a back gate layer coupled to the first barrier layer wherein the back gate layer includes a group III-V semiconductor material, a group II-VI semiconductor material, or combinations thereof, the back gate layer having a first bandgap, a second barrier layer coupled to the back gate layer wherein the second barrier layer includes a group III-V semiconductor material, a group II-VI semiconductor material, or combinations thereof, the second barrier layer having a second bandgap that is relatively larger than the first bandgap, and a quantum well channel coupled to the second barrier layer, the quantum well channel having a third bandgap that is relatively smaller than the second bandgap.

Abstract: Some exemplary embodiments of a semiconductor device using a III-nitride heterojunction and a novel Schottky structure and related method resulting in such a semiconductor device, suitable for high voltage circuit designs, have been disclosed. One exemplary structure comprises a first layer comprising a first III-nitride material, a second layer comprising a second III-nitride material forming a heterojunction with said first layer to generate a two dimensional electron gas (2DEG) within said first layer, an anode comprising at least a first metal section forming a Schottky contact on a surface of said second layer, a cathode forming an ohmic contact on said surface of said second layer, a field dielectric layer on said surface of said second layer for isolating said anode and said cathode, and an insulating material on said surface of said second layer and in contact with said anode.

Abstract: A method of manufacturing a High Electron Mobility Transistor (HEMT) may include forming first and second material layers having different lattice constants on a substrate, forming a source, a drain, and a gate on the second material layer, and changing the second material layer between the gate and the drain into a different material layer, or changing a thickness of the second material layer, or forming a p-type semiconductor layer on the second material layer. The change in the second material layer may occur in an entire region of the second material layer between the gate and the drain, or only in a partial region of the second material layer adjacent to the gate. The p-type semiconductor layer may be formed on an entire top surface of the second material layer between the gate and the drain, or only on a partial region of the top surface adjacent to the gate.

Abstract: An isolation layer for suppressing a leakage current is provided at least between a channel layer and a buffer layer formed under the channel layer in the buffer layer.

Abstract: Enhancement mode III-nitride devices are described. The 2DEG is depleted in the gate region so that the device is unable to conduct current when no bias is applied at the gate. Both gallium face and nitride face devices formed as enhancement mode devices.

Abstract: A semiconductor device includes a Si substrate having a principal plane that is a crystal surface inclined at an off angle of 0.1 degrees or less with respect to a (111) plane, an AlN layer that is provided so as to contact the principal plane of the Si substrate and is configured so that an FWHM of a rocking curve of a (002) plane by x-ray diffraction is not greater than 2000 seconds, and a GaN-based semiconductor layer formed on the AlN layer.

Abstract: High electron mobility transistors (HEMTs) and methods of manufacturing the same. A HEMT may include a source electrode, a gate electrode, a drain electrode, a channel formation layer including at least a 2-dimensional electron gas (2DEG) channel, a channel supplying layer for forming the 2DEG channel in the channel formation layer, a portion of the channel supplying layer including a first oxygen treated region. The channel supplying layer may include a second oxygen treated region that extends from the first oxygen treated region towards the drain electrode, and the depth and concentration of oxygen of the second oxygen treated region may be less than those of the first oxygen treated region.

Abstract: An integrated optical waveguide has a first optical waveguide, a second optical waveguide, and a groove. The second optical waveguide is coupled to the first optical waveguide and has a refractive index that is different from the first optical waveguide. The groove is disposed so as to traverse an optical path of the first optical waveguide and is separated from an interface between the first optical waveguide and the second optical waveguide by a predetermined spacing. The spacing from the interface and the width of the groove are determined such that reflection at a boundary between the first optical waveguide and the second optical waveguide is weakened. A semiconductor board may be disposed at a boundary between the first optical waveguide and the second optical waveguide.

Abstract: Enhancement mode III-nitride devices are described. The 2DEG is depleted in the gate region so that the device is unable to conduct current when no bias is applied at the gate. Both gallium face and nitride face devices formed as enhancement mode devices.

Abstract: A nitride semiconductor device includes: a first semiconductor layer made of first nitride semiconductor; a second semiconductor layer formed on a principal surface of the first semiconductor layer and made of second nitride semiconductor having a bandgap wider than that of the first nitride semiconductor; a control layer selectively formed on, or above, an upper portion of the second semiconductor layer and made of third nitride semiconductor having a p-type conductivity; source and drain electrodes formed on the second semiconductor layer at respective sides of the control layer; a gate electrode formed on the control layer; and a fourth semiconductor layer formed on a surface of the first semiconductor layer opposite to the principal surface, having a potential barrier in a valence band with respect to the first nitride semiconductor and made of fourth nitride semiconductor containing aluminum.

Abstract: A field effect transistor includes a layer structure made of compound semiconductor (111) provided on a semiconductor substrate (110) made of GaAs or InP, as an operation layer, and employs a first field plate electrode (116) and a second field plate electrode (118). The second field plate electrode includes a shielding part (119) located in the region between the first field plate electrode and a drain electrode (114), and serves to shield the first field plate electrode from the drain electrode. When, in the cross sectional view in the gate length direction, the length in the gate length direction of an overlap region, in which the second field plate electrode overlaps the upper part of a structure composed of the first field plate electrode and a gate electrode (113), is designated as Lol, and the gate length is Lg, the relation expressed as 0?Lol/Lg?1 holds.

Abstract: A HEMT-type field-effect semiconductor device has a main semiconductor region comprising two layers of dissimilar materials such that a two-dimensional electron gas layer is generated along the heterojunction between the two layers. A source and a drain electrode are placed in spaced positions on the main semiconductor region. Between these electrodes, with spacings therefrom, an insulator is provided with is made from a material capable of developing a stress to reduce carrier concentration in neighboring part of the two-dimensional electron gas layer, creating a discontinuity in this layer. A gate electrode overlies the insulator via a piezoelectric layer which is made from a material capable of developing, in response to a voltage applied to the gate electrode, a stress for canceling out the stress developed by the insulator.

Abstract: After creating an electron transit layer on a substrate, a baffle is formed on midpart of the surface of the electron transit layer, the surface having a pair of spaced-apart parts left on both sides of the baffle. A semiconducting material different from that of the electron transit layer is deposited on its surface thereby conjointly fabricating an electron supply layer grown continuously on the pair of spaced-apart parts of the electron transit layer surface, and a discontinuous growth layer on the baffle in the midpart of the electron transit layer surface. When no voltage is being impressed to the gate electrode on the discontinuous growth layer, this layer creates a hiatus in the two-dimensional electron gas layer generated along the heterojunction between the electron supply layer and electron transit layer. The hiatus is closed upon voltage application to the gate electrode.

Abstract: The present invention recites a new method for manufacturing Group III-N field-effect devices, such as HEMT, MOSHFET, MISHFET devices or MESFET devices, grown by Metal-Organic Vapor Phase Expitaxy, with higher performance (power), by covering the surface with a thin SiN layer on the top AlGaN layer, in the reactor where the growth takes place at high temperature, prior cooling down the structure and loading the sample out of the reactor, as well as a method to produce some HEMT transistors on those heterostructures, by depositing the contact on the surface without any removal of the SiN layer by MOCVD. The present invention recites also a device.

Abstract: A III-nitride power semiconductor device that includes a nitrogen polar active heterojunction having a two-dimensional electron gas and including a first III-nitride semiconductor body by one band gap and a second III-nitride body having another band gap over the first III-nitride semiconductor body, a gate arrangement, a gate barrier under the gate arrangement thereof, a first power electrode and a second power electrode, and a method for fabricating the device.

Abstract: In a compound semiconductor epitaxial substrate used for a strain channel high electron mobility field effect transistor which comprises an InGaAs layer as a channel layer 9 and AlGaAs layers containing n-type impurities as electron supplying layers 6 and 12, the channel layer 9 has an electron mobility at room temperature of 8300 cm2/V·s or more by adjusting an In composition of the InGaAs layer composing the channel layer 9 to 0.25 or more and optimizing the In composition and the thickness of the channel layer 9. GaAs layers 8 and 10 having a thickness of 4 nm or more each may be laminated respectively in contact with a top surface and a bottom surface of the channel layer 9.

Abstract: Metal-Semiconductor-Metal (“MSM”) photodetectors and methods to fabricate thereof are described. The MSM photodetector includes a thin heavily doped (“delta doped”) layer deposited at an interface between metal contacts and a semiconductor layer to reduce a dark current of the MSM photodetector. In one embodiment, the semiconductor layer is an intrinsic semiconductor layer. In one embodiment, the thickness of the delta doped layer is less than 100 nanometers. In one embodiment, the delta doped layer has a dopant concentration of at least 1×1018 cm?3. A delta doped layer is formed on portions of a semiconductor layer over a substrate. Metal contacts are formed on the delta doped layer. A buffer layer may be formed between the substrate and the semiconductor layer. In one embodiment, the substrate includes silicon, and the semiconductor layer includes germanium.

Abstract: A gallium nitride high electron mobility transistor, in which an inner field-plate is disposed between the gate and drain of the high electron mobility transistor, so that an electric field is distributed between gate and drain regions to reduce a peak value and to reduce gate leakage current while maintaining high frequency performance, thus obtaining a high breakdown voltage, reducing the capacitance between the gate and the drain attributable to a shielding effect, and improving linearity and high power and high frequency characteristics through variation in the input voltage of the inner field-plate.

Abstract: A Si(1-x)MxC material for heterostructures on SiC can be grown by CVD, PVD and MOCVD. SIC doped with a metal such as Al modifies the bandgap and hence the heterostructure. Growth of SiC Si(1-x)MxC heterojunctions using SiC and metal sources permits the fabrication of improved HFMTs (high frequency mobility transistors), HBTs (heterojunction bipolar transistors), and HEMTs (high electron mobility transistors).

Abstract: A III-nitride based field effect transistor obtains improved performance characteristics through manipulation of the relationship between the in-plane lattice constant of the interface of material layers. A high mobility two dimensional electron gas generated at the interface of the III-nitride materials permits high current conduction with low ON resistance, and is controllable through the manipulation of spontaneous polarization fields obtained according to the characteristics of the III-nitride material. The field effect transistor produced can be made to be a nominally on device where the in-plane lattice constants of the material forming the interface match. A nominally off device may be produced where one of the material layers has an in-plane lattice constant that is larger than that of the other layer material. The layer materials are preferably InAlGaN/GaN layers that are particularly tailored to the characteristics of the present invention.

Abstract: A high power, wide-bandgap device is disclosed that exhibits reduced junction temperature and higher power density during operation and improved reliability at a rated power density. The device includes a diamond substrate for providing a heat sink with a thermal conductivity greater than silicon carbide, a single crystal silicon carbide layer on the diamond substrate for providing a supporting crystal lattice match for wide-bandgap material structures that is better than the crystal lattice match of diamond, and a Group III nitride heterostructure on the single crystal silicon carbide layer for providing device characteristics.

Abstract: A transistor structure comprising an active semiconductor layer with metal source and drain contacts formed in electrical contact with the active layer. A gate contact is formed between the source and drain contacts for modulating electric fields within the active layer. A spacer layer is formed above the active layer and a conductive field plate formed above the spacer layer, extending a distance Lf from the edge of the gate contact toward the drain contact. The field plate is electrically connected to the gate contact and provides a reduction in the peak operational electric field.

Abstract: A field effect transistor (FET) includes a first semiconductor layer and a second semiconductor layer, the second semiconductor layer being formed on the first semiconductor layer and having a band gap energy greater than that of the first semiconductor layer. The first and second semiconductor layers are made of a Group III-V compound semiconductor layer, formed on the first semiconductor layer are a gate electrode 36 and a source electrode 35, formed on the second semiconductor layer is a drain electrode 37, and the drain electrode and the gate electrode are formed respectively on opposing planes of a semiconductor structure which contains the first and second semiconductor layers. This arrangement enables a drain's breakdown voltage to be increased in the FET, because the gate electrode 36 and the drain electrode 37 are respectively disposed, in a spatial separation of each other, on different planes instead of the same plane of the semiconductor structure.

Abstract: The present invention recites a new method for manufacturing Group III-N field-effect devices, such as HEMT, MOSHFET, MISHFET devices or MESFET devices, grown by Metal-Organic Vapor Phase Expitaxy, with higher performance (power), by covering the surface with a thin SiN layer on the top AlGaN layer, in the reactor where the growth takes place at high temperature, prior cooling down the structure and loading the sample out of the reactor, as well as a method to produce some HEMT transistors on those heterostructures, by depositing the contact on the surface without any removal of the SiN layer by MOCVD. The present invention recites also a device.

Abstract: A field effect transistor including an i-type first semiconductor layer and a second semiconductor layer formed on the first semiconductor layer and having a band gap energy higher in magnitude than that of the first semiconductor layer. The first semiconductor layer and second semiconductor layer are each made of a gallium nitride-based compound semiconductor layer. A gate electrode is formed on the second semiconductor layer and a second electrode is formed on the first semiconductor layer. Thus, the field effect transistor is constructed in such a manner as the first semiconductor layer and second semiconductor layer are interposed between the gate electrode and the second electrode. Thus field effect transistor is able to discharge the holes that are accumulated in the channel from the elemental structure and to improve the withstand voltage of the field effect transistor.

Abstract: A heterojunction field effect transistor includes a laminated body. The laminated body includes a channel layer of GaN, an electron supply layer of AlN or AlxGa1-xN (0.6?x<1) formed on the channel layer, and a cap layer of GaN formed on the electron supply layer.

Abstract: A semiconductor integrated circuit device includes a HFET formed on part of a substrate made of sapphire and including a Group III-V nitride semiconductor layer, a dielectric film formed on the substrate to cover the top and side surfaces and upper corners of the Group III-V nitride semiconductor layer, a microstrip line formed with the dielectric film interposed between the substrate and the microstrip line, and a drain lead which is formed on part of the dielectric film and through which the HFET is electrically connected to the microstrip line.

Abstract: A field-effect transistor includes a channel layer having a channel and a carrier supply layer, disposed on the channel layer, containing a semiconductor represented by the formula AlxGa1-xN, wherein x is greater than 0.04 and less than 0.45. The channel is formed near the interface between the channel layer and the carrier supply layer or depleted, the carrier supply layer has a band gap energy greater than that of the channel layer, and x in the formula AlxGa1-xN decreases monotonically with an increase in the distance from the interface. The channel layer may be crystalline of gallium nitride. The channel layer may be undoped. X of the formula AlxGa1-xN of the carrier supply layer is greater than or equal to 0.15 and less than or equal to 0.40 at the interface.