Abstract: Contacts for solar cells and other optoelectronic devices are provided. Embodiments described herein take advantage of the surface Fermi level pinning effect to build an electrical field inside of a semiconductor to extract or inject carriers for solar cells, photodetectors, and light-emitting device applications. For example, n-type or p-type two-dimensional (2D) materials can be used in contact with an n-type semiconductor to form a “p-region” so that a p-n junction, or an i-n or n-n+ junction can be constructed. Similarly, n-type or p-type 2D materials can be used in contact with a p-type semiconductor to form an “n-region” so that an n-p junction, or an i-p or p-p+ junction can be constructed. These structures can provide sufficiently high electrical field inside the semiconductor to extract photogenerated carriers in solar cells and photodetectors or inject minority carriers for light-emitting devices.

Abstract: High-performance long-lifetime charge-separation photodetectors are provided. A new device design is described based on novel band structure engineering of semiconductor materials for photodetectors, such as photosensors, solar cells, and thermophotovoltaic devices. In an exemplary aspect, photodetectors described herein include a charge-separated photo absorber region. This comprises a semiconductor with a band structure that has an indirect fundamental bandgap, with a direct bandgap (?-? transition) only slightly above the indirect fundamental bandgap (L- or X-? transitions) (e.g., approximately equal to or larger than an energy of a product of the Boltzmann constant (kB), and temperature (T), with kBT=26 millielectron-volts (meV) at room temperature). This design not only improves photogenerated-carrier lifetime (similar to indirect bandgap semiconductors), but also maintains a strong absorption coefficient (similar to direct bandgap semiconductors).

Abstract: Devices converting light to electricity (such as solar cells or photodetectors) including a heavily-doped p-type a-SiCy:H and an i-MgxCd1-xTe/n-CdTe/N—Mg0.24Cd0.76Te double heterostructure (DH), with power conversion efficiency of as high as 17%, Voc as high as 1.096 V, and all operational characteristics being substantially better than those of monocrystalline solar cells known to-date. The a-SiCy:H layer is configured to enable high built-in potential while, at the same time, allowing the doped absorber to maintain a very long carry lifetime. In comparison, similar undoped CdTe/MgxCd1-xTe DH designs reveal a long carrier lifetime of 3.6 ?s and an interface recommendation velocity of 1.2 cm/s, which are lower than the record values reported for GaAs/Al0.5Ga0.5As (18 cm/s) and GaAs/Ga0.5In0.5P (1.5 cm/s) DHs.

Abstract: Devices converting light to electricity (such as solar cells or photodetectors) including a heavily-doped p-type a-SiCy:H and an i-MgxCd1?xTe/n-CdTe/N—Mg0.24Cd0.76Te double heterostructure (DH), with power conversion efficiency of as high as 17%, Voc as high as 1.096 V, and all operational characteristics being substantially better than those of monocrystalline solar cells known to-date. The a-SiCy:H layer is configured to enable high built-in potential while, at the same time, allowing the doped absorber to maintain a very long carry lifetime. In comparison, similar undoped CdTe/MgxCd1?xTe DH designs reveal a long carrier lifetime of 3.6 ?s and an interface recommendation velocity of 1.2 cm/s, which are lower than the record values reported for GaAs/Al0.5Ga0.5As (18 cm/s) and GaAs/Ga0.5In0.5P (1.5 cm/s) DHs.

Abstract: A CCD with an internal heterostructure well to store the photogenerated carriers is realized by using barrier and absorber semiconductors with a type-II band alignment in nBn or pBp photodetectors to form a specific barrier configured to confine the depletion region and a well to trap and store the photogenerated minority carriers. Depending on the spectral regime, (InAs/InAsSb)/(InAs/AlGaSb) superlattices can be used in the infrared, Si/Ge or AlP/GaP in the visible portion of optical spectrum, and GaN/ZnO in the UV portion. The resulting device not only leverages the advantages of the conventional CCD (such as in-pixel signal integration to suppress the noise), but also boasts an advantageously low operational voltage, thereby ensuring the low power consumption and low band-to-band tunneling current/noise (in particular, for use as an infrared photodetector).

Abstract: Systems and methods for a real-time baseline correction technique for infrared time-resolved photoluminescence are disclosed.

Abstract: A CCD with an internal heterostructure well to store the photogenerated carriers is realized by using barrier and absorber semiconductors with a type-II band alignment in nBn or pBp photodetectors to form a specific barrier configured to confine the depletion region and a well to trap and store the photogenerated minority carriers. Depending on the spectral regime, (InAs/InAsSb)/(InAs/AlGaSb) superlattices can be used in the infrared, Si/Ge or AlP/GaP in the visible portion of optical spectrum, and GaN/ZnO in the UV portion. The resulting device not only leverages the advantages of the conventional CCD (such as in-pixel signal integration to suppress the noise), but also boasts an advantageously low operational voltage, thereby ensuring the low power consumption and low band-to-band tunneling current/noise (in particular, for use as an infrared photodetector).

Abstract: A pulsed voltage bias method and/or pulsed light bias method may be used to reduce, minimize, and/or eliminate external quantum efficiency measurement artifacts of multi-junction solar cells, for example artifacts caused by the shunt effect. In this manner, multi-junction solar cells may be designed and constructed with improved performance, efficiency, and the like.

Abstract: Systems and methods for a real-time baseline correction technique for infrared time-resolved photoluminescence are disclosed.

Abstract: Tandem solar cells are provided that are more cost-efficient manner and can reach much higher power conversion efficiency compared to previous technologies. In some aspects, a tandem solar cell includes a first subcell configured to absorb a first portion of a solar spectrum, wherein at least one layer of the first subcell is polycrystalline, and a second subcell configured to absorb a second portion of the solar spectrum, wherein the second subcell is electrically connected to the first subcell through a conductive contact, and includes at least one textured surface.

Abstract: Multi-band photodetectors can be formed by series connecting unipolar and, optionally, bipolar semiconductor structures, each having different photodetection bands. Under default mode of operation, the detector with highest resistance and lowest current will be the current limiting device and will be the active photodetector. When the active photodetector is illuminated with strong light in its own detection band it will be optically biased. This active photodetector will no longer be the highest resistance device, and the next photodetector will be the active photodetector. Repeating this operation pattern, allows switching photodetection bands of the multi-band photodetector. The resistances, dark current and photocurrent of the devices should be engineered to have proper switching. Moreover, the illuminating surface, and photodetector placement should be optimized for proper light biasing. The current passing through the device will always be equal to the current of the active photodetector.

Abstract: Use of semiconductor materials having a lattice constant of within +/?1.6% of 6.1 angstroms facilitates improved semiconductor device performance and new semiconductor structures, for example integration of field-effect devices and optoelectronic devices on a single wafer. High-mobility channels are enabled, improving device performance.

Abstract: To improve the efficiency of heterostructure silicon photovoltaic devices, II-VI wide bandgap semiconductor layers can replace the TCO/doped amorphous silicon/intrinsic amorphous silicon layers on the front side or on both sides of the silicon bulk layer. For example, photovoltaic devices are described containing a first contact electrode; a first doped II-VI semiconductor layer disposed over the first contact electrode; a doped crystalline silicon layer disposed over the first doped II-VI semiconductor layer; and a second contact electrode disposed over the doped silicon layer, where one of the doped crystalline silicon layer and the first doped II-VI semiconductor layer is n-doped N and the other is p-doped.

Abstract: Described herein are diffraction gratings and methods for the manufacture thereof. One method comprises applying a force to a substrate to strain the substrate, disposing a thin film on at least a portion of the substrate, and reducing the force applied to the substrate, thereby causing the thin film to buckle.

Abstract: Use of semiconductor materials having a lattice constant of within +/?1.6% of 6.1 angstroms facilitates improved semiconductor device performance and new semiconductor structures, for example integration of field-effect devices and optoelectronic devices on a single wafer. High-mobility channels are enabled, improving device performance.

Abstract: Two-terminal multi junction photodetectors and focal plane arrays for multi-color detection or imaging acquisition can be formed by connecting photodiodes with different bandgaps or wavelengths, through tunnel diodes, in series with the same polarization. Under reverse bias in the dark, the total current going through such multi junction photodetectors is dictated by the smallest reverse saturation current of the photodiodes. When in operating mode, a set of light sources with different wavelengths corresponding to each individual photodiode can be used to optically bias all the photodiodes except the detecting photodiode Under illumination, all other photodiodes work in the photovoltaic mode and have much higher maximum possible reverse currents than the detecting photodiode. As a result, the total current of the multi junction photodetector is dictated by the detecting photodiode.

Abstract: Described herein are diffraction gratings and methods for the manufacture thereof. One method comprises applying a force to a substrate to strain the substrate, disposing a thin film on at least a portion of the substrate, and reducing the force applied to the substrate, thereby causing the thin film to buckle.

Abstract: Lattice-matched II-VI (ZnCdHg)(SeTe) and III-V (InGaAsP) semiconductors grown on InP substrates can be used for preparing multi junction solar cells that can potentially reach efficiencies greater than 40% under one sun. For example, a semiconductor structure can be prepared comprising, an InP substrate; an optional InGaAsP building block formed over the InP substrate; an InP building block formed over either the InGaAsP building block, when present, or the InP substrate and at least one (ZnCdHg)(SeTe) building block formed over the InP building block.

Abstract: The present invention provides semiconductor structures comprising a substrate and at least three III-V and/or II-VI multi junction building blocks, each comprising a p-n junction having at least two alloy layers, formed over the substrate, provided at least one multi-junction building block comprises II-VI alloy layers. Further described are methods for preparing semiconductor structures utilizing a sacrificial or etch-stop ternary III-V alloy layer over an III-V substrate.

Abstract: A single mode high power laser device such as a VCSEL is formed with two oxide apertures, one on each side of the active region or cavity. The sizes of the apertures and the distances from the apertures to the cavity center are chosen or optimum, near-Gaussian current density distribution. The high power of a VCSEL thus formed is improved still more by good heat removal by either formation of a via through the substrate and gold plating on top and bottom of the VCSEL (including the via) or by lifting the VCSEL structure from the substrate and locating it on a heat sink.