Triple-junction GaInP/GaAs/GaInNAs solar cells with conversion efficiency of~29% at AM0 are demonstrated using a combination of molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD) processes. The bottom junction made of GaInNAs was first grown on a GaAs substrate by MBE and then transferred to an MOCVD system for subsequent overgrowth of the two top junctions. The process produced repeatable cell characteristics and uniform efficiency pattern over 4-inch wafers. Combining the advantages offered by MBE and MOCVD opens a new perspective for fabrication of high-efficiency tandem solar cells with three or more junctions.

An exclusive advantage of semiconductor spintronics is its potential for optospintronics that will allow integration of spin-based information processing/storage with photon-based information transfer/communications. Unfortunately, progresses have so far been severely hampered by the failure to generate nearly fully spin-polarized charge carriers in semiconductors at room temperature. Here, we demonstrate successful generation of conduction electron spin polarization exceeding 90% at room temperature without a magnetic field in a non-magnetic all-semiconductor nanostructure, which remains high even up to 110°C. This is accomplished by remote spin filtering of InAs quantum-dot electrons via an adjacent tunneling-coupled GaNAs spin filter. We further show that the quantum-dot electron spin can be remotely manipulated by spin control in the adjacent spin filter, paving the way for remote spin encoding and writing of quantum memory as well as for remote spin control of spin-photon interfaces. This work demonstrates the feasibility to implement opto-spintronic functionality in common semiconductor nanostructures.

Monolithic four-junction solar cells incorporating two dilute nitride (GaInNAsSb) bottom junctions are reported. The dilute nitride junctions have band gaps of 0.9 and 1.2 eV, while the top junctions have band gaps of 1.4 and 1.9 eV. By using experimental-based parametrization, it was estimated that the four-junction solar cell could theoretically exhibit efficiency levels of 34.7% at one sun, 43.2% at 100 suns, and 46.4% at 1000 suns for AM1.5D illumination. The most challenging subcell in terms of fabrication is the GaInNAsSb bottom junction with 0.9 eV band gap. For this subcell, a background doping level down to 5 × 10 14 cm −3 and a high charge carrier lifetime up to 2 to 4 nanoseconds are reported, which reflects high values for current and voltage. An experimental AlGaAs/GaAs/GaInNAsSb/GaInNAsSb solar cell structure was fabricated by molecular beam epitaxy. At one-sun AM1.5D illumination, the experimental cell exhibited an efficiency of 25%, an average quantum efficiency of 91%, and an open circuit voltage, which is about 87% of the estimated potential.The cell exhibited maximum efficiency of 37% at 100-sun concentration.

No abstract

A new method for modification of planar multilayer structures to create nanostructured aluminum oxide anti-reflection coatings is reported. The method is non-toxic and low-cost, being based on treatment of the coating with heated de-ionized water after the deposition of aluminum oxide. The results show that the method provides a viable alternative for attaining a low reflectance ARC. In particular, a low average reflectivity of ∼3.3% is demonstrated in a broadband spectrum extending from 400 nm to 2000 nm for ARCs deposited on GaInP solar-cells, the typical material used as top-junction in solar cell tandem architectures. Moreover, the process is compatible with volume manufacturing technologies used in photovoltaics, such as ion beam sputtering and electron beam evaporation.