In some embodiments, the techniques described herein relate to an epitaxial oxide transistor. The transistor can include: a substrate; a channel layer including a first epitaxial semiconductor layer on the substrate; a gate layer including a second epitaxial semiconductor layer on the first epitaxial semiconductor layer; a source electrode and a drain electrode coupled to the channel layer; and a gate electrode coupled to the gate layer. The first epitaxial semiconductor layer can include a first polar oxide material and the second epitaxial semiconductor layer can include a second polar oxide material. The first polar oxide material and the second polar oxide material can include cation-polar surfaces oriented towards or away from the substrate, and the second polar oxide material can include a wider bandgap than the first polar oxide material.

A light-emitting device includes a first semiconductor layer; an active layer on the first semiconductor layer and having an upmost surface with a first width; and a second semiconductor layer on the active layer and having a bottommost surface with a second width less than the active layer.

A light-emitting device includes a first semiconductor layer; an active layer on the first semiconductor layer and having an upmost surface with a first width; and a second semiconductor layer on the active layer and having a bottommost surface with a second width less than the active layer.

A nitride semiconductor ultraviolet light-emitting element is provided. The element includes a light-emitting element structure part with an n-type layer, an active layer, and a p-type layer stacked vertically, which are made of AlGaN-based semiconductors with wurtzite structure. The n-type layer has an n-type AlGaN-based semiconductor, the active layer has well layers including an AlGaN based semiconductor, and the p-type layer has a p-type AlGaN-based semiconductor. Each semiconductor layer in the n-type and the active layers is an epitaxially grown layer having a surface on which multi-step terraces parallel to the (0001) plane are formed. The n-type layer has first Ga-rich regions which include n-type AlGaN regions in which an AlGaN composition ratio is an integer ratio of Al.sub.2Ga.sub.1N.sub.3. The well layer includes a second Ga-rich region, which includes an AlGaN region in which an AlGaN composition ratio is an integer ratio of Al.sub.1Ga.sub.1N.sub.2 or Al.sub.5Ga.sub.7N.sub.12.

A nitride semiconductor ultraviolet light-emitting element is provided. The element includes a light-emitting element structure part with an n-type layer, an active layer, and a p-type layer stacked vertically, which are made of AlGaN-based semiconductors with wurtzite structure. The n-type layer has an n-type AlGaN-based semiconductor, the active layer has well layers including an AlGaN based semiconductor, and the p-type layer has a p-type AlGaN-based semiconductor. Each semiconductor layer in the n-type and the active layers is an epitaxially grown layer having a surface on which multi-step terraces parallel to the (0001) plane are formed. The n-type layer has first Ga-rich regions which include n-type AlGaN regions in which an AlGaN composition ratio is an integer ratio of Al.sub.2Ga.sub.1N.sub.3. The well layer includes a second Ga-rich region, which includes an AlGaN region in which an AlGaN composition ratio is an integer ratio of Al.sub.1Ga.sub.1N.sub.2 or Al.sub.5Ga.sub.7N.sub.12.

A light emitting element may include: a light emitting element core including a first semiconductor layer, a second semiconductor layer, and a light emitting layer between the first semiconductor layer and the second semiconductor layer; and a single crystal insulating layer around a side surface of the light emitting element core.

A light emitting element may include: a light emitting element core including a first semiconductor layer, a second semiconductor layer, and a light emitting layer between the first semiconductor layer and the second semiconductor layer; and a single crystal insulating layer around a side surface of the light emitting element core.

Semiconductor structures and methods for forming those semiconductor structures are disclosed. A semiconductor structure can include a growth axis, a first layer consisting of a single layer, and a second layer. The single layer can include: a first semiconductor with a polar crystal structure; and a monotonic change in composition from a wider band gap (WBG) material to a narrower band gap (NBG) material or from a NBG material to a WBG material along the growth axis. The monotonic change in composition can induce p-type or n-type conductivity in the first layer. The second layer can include a second semiconductor with the polar crystal structure. There is no abrupt change in polarization at an interface between the first layer and the second layer, and the monotonic change in composition is the only monotonic change in composition in the semiconductor structure.

Semiconductor structures and methods for forming those semiconductor structures are disclosed. A semiconductor structure can include a growth axis, a first layer consisting of a single layer, and a second layer. The single layer can include: a first semiconductor with a polar crystal structure; and a monotonic change in composition from a wider band gap (WBG) material to a narrower band gap (NBG) material or from a NBG material to a WBG material along the growth axis. The monotonic change in composition can induce p-type or n-type conductivity in the first layer. The second layer can include a second semiconductor with the polar crystal structure. There is no abrupt change in polarization at an interface between the first layer and the second layer, and the monotonic change in composition is the only monotonic change in composition in the semiconductor structure.

Provided are an ultraviolet emitting optical device and an operating method thereof. The ultraviolet emitting optical device includes a substrate, a first encapsulation layer, an active layer and a second encapsulation layer sequentially stacked on the substrate, a first electrode layer between the first encapsulation layer and the active layer, a second electrode layer between the active layer and the second encapsulation layer, and color centers provided in the active layer, wherein the active layer includes hexagonal boron nitride (hBN), wherein the color centers are configured to emit light in an ultraviolet wavelength range.