A nitride semiconductor device includes a SiC substrate having a hexagonal crystal structure and including a main surface inclined with respect to a c-plane at an off-angle from 2 to 6 in a specific crystal direction, a nitride semiconductor layer located on the main surface of the SiC substrate and including an electron transit layer and an electron supply layer, and a gate electrode, a source electrode, and a drain electrode located on the nitride semiconductor layer. The main surface is parallel to a first direction, a second direction orthogonal to the first direction, and a third direction coinciding with the specific crystal direction in plan view. The source electrode and the drain electrode are separated in the first direction. The gate electrode extends in the second direction between the source electrode and the drain electrode. The first direction intersects the third direction at an angle of 9015.

According to one embodiment, a nitride semiconductor includes a base body, a nitride member, and an intermediate region provided between the base body and the nitride member. The nitride member includes a first nitride region including Al.sub.x1Ga.sub.1-x1N (0<x11), and a second nitride region including Al.sub.x2Ga.sub.1-x2N (0x2<1, x2<x1). The first nitride region is between the intermediate region and the second nitride region. The intermediate region includes nitrogen and carbon. A concentration of carbon in the intermediate region is not less than 1.510.sup.19/cm.sup.3 and not more than 610.sup.20/cm.sup.3.

An object is to obtain a semiconductor device having a high sensitivity in detecting signals and a wide dynamic range, using a thin film transistor in which an oxide semiconductor layer is used. An analog circuit is formed with the use of a thin film transistor including an oxide semiconductor which has a function as a channel formation layer, has a hydrogen concentration of 510.sup.19 atoms/cm.sup.3 or lower, and substantially functions as an insulator in the state where no electric field is generated. Thus, a semiconductor device having a high sensitivity in detecting signals and a wide dynamic range can be obtained.

A semiconductor device includes an insulating substrate, a conductor pattern formed on the insulating substrate, and a plurality of semiconductor elements provided on the conductor pattern and electrically connected in parallel, wherein the conductor pattern has a minimum rectangular region surrounding the plurality of semiconductor elements in a plan view, each semiconductor element of the plurality of semiconductor elements has an epitaxial layer of a first conductivity type, the plurality of semiconductor elements include a first semiconductor element located nearest to a center of gravity of the rectangular region, and a second semiconductor element located farthest from the center of gravity of the rectangular region, and a first impurity concentration in the epitaxial layer of the first semiconductor element is higher than a second impurity concentration in the epitaxial layer of the second semiconductor element.

Provided is a semiconductor device, including: a drift region of a first conductivity type which is provided in a semiconductor substrate, and a buffer region of the first conductivity type which is provided between the drift region and a lower surface of the semiconductor substrate, and has three or more concentration peaks higher than a doping concentration of the drift region of the semiconductor substrate in a depth direction. Three or more of the concentration peaks includes a shallowest peak closest to the lower surface of the semiconductor substrate, a high concentration peak arranged at an upper side than the lower surface of the semiconductor substrate than the shallowest peak, and one or more low concentration peaks arranged at an upper side than the lower surface of the semiconductor substrate than the high concentration peak and of which the doping concentration is or less of the high concentration peak.

A process of forming a gate insulating film in a silicon carbide semiconductor device. The process includes performing a first stage of a nitriding heat treatment by a gas containing oxygen and nitrogen, followed by depositing an oxide film, and then performing a second stage of the nitriding heat treatment by a gas containing nitric oxide and nitrogen. The amount of nitrogen at the treatment starting point of the first stage of the nitriding heat treatment is greater than the amount of nitrogen at the treatment starting point of the second stage of the nitriding heat treatment. The amount of nitrogen at the treatment ending point of the second stage of the nitriding heat treatment is greater than the amount of nitrogen at the treatment ending point of the first stage of the nitriding heat treatment.

A semiconductor rectifier device includes: an epitaxial layer, having a top surface and a bottom surface; a first doped region having a first conductivity type, located in the epitaxial layer; a first trench structure, located in the first doped region; a second trench structure adjacent to the first trench structure, located in the first doped region; a second doped region having a second conductivity type, located in the epitaxial layer between the first trench structure and the second trench structure, wherein a depth of the second doped region is less than a depth of the first trench structure; and a metal layer, located on the top surface of the epitaxial layer, covering the first trench structure, the second trench structure, and the second doped region, wherein the metal layer is in contact with the top surface, forming a Schottky interface.

An object is to obtain a semiconductor device having a high sensitivity in detecting signals and a wide dynamic range, using a thin film transistor in which an oxide semiconductor layer is used. An analog circuit is formed with the use of a thin film transistor including an oxide semiconductor which has a function as a channel formation layer, has a hydrogen concentration of 510.sup.19 atoms/cm.sup.3 or lower, and substantially functions as an insulator in the state where no electric field is generated. Thus, a semiconductor device having a high sensitivity in detecting signals and a wide dynamic range can be obtained.

A doping concentration distribution in an accumulation region in a depth direction of a semiconductor substrate has a maximum portion at which a doping concentration reaches a maximum value, an upper gradient portion in which the concentration decreases from the maximum portion to a base region, a lower gradient portion in which the concentration decreases from the maximum portion to a drift region, and a kink portion at which a differential value of the doping concentration distribution exhibits an extreme value in a region except a region in which the differential value exhibits a maximum value or a minimum value.

A semiconductor device includes a semiconductor layer of a first conductivity type that has a main surface and that includes a device region, a base region of a second conductivity type that is formed in a surface layer portion of the main surface at the device region, a source region of the first conductivity type that is formed in a surface layer portion of the base region at an interval inward from a peripheral portion of the base region and that defines a channel region with the semiconductor layer, a base contact region of the second conductivity type that is formed in a region different from the source region at the surface layer portion of the base region and that has an impurity concentration exceeding an impurity concentration of the base region, a well region of the first conductivity type that is formed in the surface layer portion of the main surface at an interval from the base region at the device region and that defines a drift region with the base region, a drain region of the first conductivity type that is formed in a surface layer portion of the well region, an impurity region of the second conductivity type that is formed in the surface layer portion of the well region and that is electrically connected to the drain region, and a gate structure that has a gate insulating film covering the channel region on the main surface and a gate electrode facing the channel region on the gate insulating film and electrically connected to the source region and the base contact region.