A semiconductor device includes: a first semiconductor layer having an N conductive type and made of a gallium oxide-based semiconductor; and a second semiconductor layer made of a gallium oxide-based semiconductor, in contact with the first semiconductor layer, and having the N conductive type with an electrically active donor concentration higher than an electrically active donor concentration of the first semiconductor layer. A difference between a donor concentration of the first semiconductor layer and a donor concentration of the second semiconductor layer is smaller than a difference between the electrically active donor concentration of the first semiconductor layer and the electrically active donor concentration of the second semiconductor layer.

A semiconductor device includes: a first semiconductor layer having an N conductive type and made of a gallium oxide-based semiconductor; and a second semiconductor layer made of a gallium oxide-based semiconductor, in contact with the first semiconductor layer, and having the N conductive type with an electrically active donor concentration higher than an electrically active donor concentration of the first semiconductor layer. A difference between a donor concentration of the first semiconductor layer and a donor concentration of the second semiconductor layer is smaller than a difference between the electrically active donor concentration of the first semiconductor layer and the electrically active donor concentration of the second semiconductor layer.

A semiconductor device includes: a first semiconductor layer having an N conductive type and made of a gallium oxide-based semiconductor; and a second semiconductor layer made of a gallium oxide-based semiconductor, in contact with the first semiconductor layer, and having the N conductive type with an electrically active donor concentration higher than an electrically active donor concentration of the first semiconductor layer. A difference between a donor concentration of the first semiconductor layer and a donor concentration of the second semiconductor layer is smaller than a difference between the electrically active donor concentration of the first semiconductor layer and the electrically active donor concentration of the second semiconductor layer.

A thin film transistor includes an active layer, a gate electrode spaced apart from and partially overlapped with the active layer, and a gate insulating film between the active layer and the gate electrode, wherein the active layer includes a channel portion overlapped with the gate electrode, a conductorization portion which is not overlapped with the gate electrode, and a gradient portion between the channel portion and the conductorization portion and not overlapped with the gate electrode, the conductorization portion and the gradient portion of the active layer are doped with a dopant, the gate insulating film covers an upper surface of the active layer facing the gate electrode during doping of the active layer, and in the gradient portion, a concentration of the dopant increases along a direction from the channel portion toward the conductorization portion. A display device may also include the thin film transistor.

A planar insulating spacer layer is formed over a substrate, and a vertical stack of a gate electrode, a gate dielectric layer, and a first semiconducting metal oxide layer may be formed thereabove. The first semiconducting metal oxide layer includes atoms of a first n-type dopant at a first average dopant concentration. A second semiconducting metal oxide layer is formed over the first semiconducting metal oxide layer. Portions of the second semiconducting metal oxide layer are doped with the second n-type dopant to provide a source-side n-doped region and a drain-side n-doped region that include atoms of the second n-type dopant at a second average dopant concentration that is greater than the first average dopant concentration. Various dopants may be introduced to enhance performance of the thin film transistor.

A planar insulating spacer layer is formed over a substrate, and a vertical stack of a gate electrode, a gate dielectric layer, and a first semiconducting metal oxide layer may be formed thereabove. The first semiconducting metal oxide layer includes atoms of a first n-type dopant at a first average dopant concentration. A second semiconducting metal oxide layer is formed over the first semiconducting metal oxide layer. Portions of the second semiconducting metal oxide layer are doped with the second n-type dopant to provide a source-side n-doped region and a drain-side n-doped region that include atoms of the second n-type dopant at a second average dopant concentration that is greater than the first average dopant concentration. Various dopants may be introduced to enhance performance of the thin film transistor.

A method for producing a 3D semiconductor device, the method comprising: providing a first level, said first level comprising a first single crystal layer; forming first alignment marks and control circuits in and/or on said first level, wherein said control circuits comprise first single crystal transistors, and wherein said control circuits comprise at least two interconnection metal layers; forming at least one second level disposed on top of said control circuits; performing a first etch step into said second level; and performing additional processing steps to form a plurality of first memory cells within said second level, wherein each of said memory cells comprise at least one second transistors, and wherein said additional processing steps comprise depositing a gate electrode for said second transistors.

A method for manufacturing a semiconductor device includes: preparing a substrate made of a compound semiconductor containing a first element and a second element that is bonded to the first element and has an electronegativity smaller than that of the first element by 1.5 or more; causing an electric current to flow in the substrate; and dividing the substrate at a position including a current region where the electric current is caused to flow and along a cleavage plane of the substrate. A method for manufacturing a semiconductor device includes: stacking a first substrate and a second substrate each made of the compound semiconductor; and bonding the first substrate and the second substrate by causing an electric current to flow between the first substrate and the second substrate.

A method for manufacturing a semiconductor device includes: preparing a substrate made of a compound semiconductor containing a first element and a second element that is bonded to the first element and has an electronegativity smaller than that of the first element by 1.5 or more; causing an electric current to flow in the substrate; and dividing the substrate at a position including a current region where the electric current is caused to flow and along a cleavage plane of the substrate. A method for manufacturing a semiconductor device includes: stacking a first substrate and a second substrate each made of the compound semiconductor; and bonding the first substrate and the second substrate by causing an electric current to flow between the first substrate and the second substrate.

A planar insulating spacer layer is formed over a substrate, and a vertical stack of a gate electrode, a gate dielectric layer, and a first semiconducting metal oxide layer may be formed thereabove. The first semiconducting metal oxide layer includes atoms of a first n-type dopant at a first average dopant concentration. A second semiconducting metal oxide layer is formed over the first semiconducting metal oxide layer. Portions of the second semiconducting metal oxide layer are doped with the second n-type dopant to provide a source-side n-doped region and a drain-side n-doped region that include atoms of the second n-type dopant at a second average dopant concentration that is greater than the first average dopant concentration. Various dopants may be introduced to enhance performance of the thin film transistor.