Enhanced optical gain and lasing in indirect gap semiconductor thin films and nanostructures

摘要

Structures and methodologies to obtain lasing in indirect gap semiconductors such as Ge and Si are provided and involves excitonic transitions in the active layer comprising of at least one indirect gap layer. Excitonic density is increased at a given injection current level by increasing their binding energy by the use of quantum wells, wires, and dots with and without strain. Excitons are formed by holes and electrons in two different layers that are either adjacent or separated by a thin barrier layer, where at least one layer confining electrons and holes is comprised of indirect gap semiconductor such as Si and Ge, resulting in high optical gain and lasing using optical and electrical injection pumping.

主权项

1. a semiconductor laser structure comprising, an active layer, first and second barrier layers on either side of the active layer, first and second cladding layers, and a substrate,
wherein the active layer includes a plurality of cladded Ge quantum dots, wherein the Ge quantum dot cladding is selected from GeOx, ZnMgSSe, ZnSe, ZnSSe, wherein each of plurality of the cladded Ge quantum dots have a 3-4 nm single crystal Ge core and a 0.5-1 nm cladding such that cladding between adjacent Ge cores range from 1-2 nm, wherein the plurality of cladded Ge quantum dots form superlattice like mini-energy bands that correspond to indirect and direct energy gap states, wherein the superlattice like mini-energy bands include a conduction mini-energy bands and a valence mini-energy bands, wherein conduction band includes indirect and direct energy bands, wherein the first and second barrier layers sandwich the plurality of cladded Ge quantum dot confine electrons in the conduction mini-energy bands and holes in the valence mini-energy bands, wherein the first barrier layer is disposed between the substrate and the active layer, and said second barrier layer is located on the other side of the active layer, wherein the active layer and two barrier layers form a waveguide region to confine photons, wherein the first and second barrier layers have energy gap greater than the energy gap between the conduction and valence mini-energy bands responsible for light emission from direct gap mini-energy band states of said plurality of cladded Ge quantum dot layer, wherein the first cladding layer is located between the substrate and the first barrier layer, wherein the second cladding layer is located on the second barrier layer, wherein the first and second cladding layers have an index of refraction configured to confine photons in the waveguide region, wherein photons are emitted when electrons and holes are injected in the plurality of cladded Ge quantum dots, wherein the first and second cladding layers are selected from materials that do not absorb photons and that have an energy gap greater than the energy gap due to mini-energy conduction band and valence bands of the active layer, wherein the active layer, first and second barrier layers, and the first and second cladding layers are configured to include at least one carrier injection mechanism selected from a p-n double heterojunction, a p-n single heterojunction, and a metal-oxide- semiconductor (MOS) device, wherein when the semiconductor laser structure is configured and baised as p-n double heterojunctions, p-n single heterojunction, and MOS device such that injected electron and hole populations are filling the indirect mini-energy band states and facilitating transitions between direct conduction mini-energy band and valence mini-energy band in the plurality of cladded Ge quantum dots, wherein the p-n double heterojunction is formed by the first and second barrier layers, and at least one of the first and second cladding layers, wherein the first and second cladding layer are configured to form either a p-n double heterojunction or a p-n single heterojunction, wherein the cladding layers are doped with opposite electrical conductivity type wherein doping concentration is in the range of 1018-1019 cm−3, wherein the substrate is selected from Si, Si-on-insulator, Ge-on-insulator, II-VI and III-V semiconductors, wherein when the semiconductor laser structure is configured as a metal-oxide semiconductor (MOS) device, it includes an n+-type source, a p+-type drain, a gate insulator layer and a gate layer, wherein the active layer comprising of cladded Ge quantum dots is disposed between the n+-type source and p+-type drain under the gate insulator layer, wherein the gate insulator layer serving as the second barrier layer, wherein when the gate layer and n+-type source are biased above a threshold voltage, wherein the n+-type source provides electrons to the plurality cladded Ge quantum dot layer which forms an inversion layer, wherein the gate layer is deposited with a second cladding layer, wherein the active layer comprising plurality of cladded Ge quantum dots, n+-type source and p+-type drain are disposed on p-semiconductor layer, wherein the p-semiconductor layer serving as the first barrier layer, wherein the p+-type drain is isolated from the inversion layer and the gate layer and supplies holes when n+-type source and p+-type drain are biased making p+-type drain positive than said n+-type source, wherein the p-semiconductor layer is disposed on the substrate
wherein the substrate is configured to serve as the first cladding layer to confine emitted photons, wherein the semiconductor laser structure is configurable as either a cavity feedback type laser, or a distributed feedback laser, wherein the cavity feedback type laser structure is either an edge-emitting laser type or a surface-emitting configuration, wherein the distributed feedback laser type structure is either an edge-emitting type or a surface-emitting type.