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. Copyright © 2016 John Wiley & Sons, Ltd.

The first monolithic GaAs-based vertical-external-cavity surface-emitting laser (VECSEL) operating at 1550 nm is reported. The VECSEL operation is based on a gain mirror which was grown in a single growth run by plasma-assisted molecular beam epitaxy. The gain mirror comprised eight GaInNAsSb/GaAs quantum wells with a photoluminescence peak at 1505 nm and an AlAs/GaAs distributed Bragg reflector ensuring high reflectivity. The VECSEL chip was pumped with an 808-nm diode laser that had a large quantum defect in respect to the lasing wavelength. An output power of 80 mW in continuous wave mode and 210 mW in pulsed pump mode are demonstrated close to room temperature.

We report the temperature coefficients for MBE-grown GaInP/GaAs/GaInNAsSb multijunction solar cells and the corresponding single junction sub-cells. Temperature-dependent current-voltage measurements were carried out using a solar simulator equipped with a 1000 W Xenon lamp and a three-band AM1.5D simulator. The triple-junction cell exhibited an efficiency of 31% at AM1.5G illumination and an efficiency of 37–39% at 70x real sun concentration. The external quantum efficiency was also measured at different temperatures. The temperature coefficients up to 80°C, for the open circuit voltage, the short circuit current density, and the conversion efficiency were determined to be −7.5 mV/°C, 0.040 mA/cm2/°C, and −0.09%/°C, respectively.

We report on the progress in developing lattice‐matched GaAs‐based solar cells with focus on developing AlGaInP, AlGaAs, and GaInNAsSb materials, aiming at achieving a wide spectral coverage, that is, 0.7–2.2 eV. To this end, we first benchmark the performance of an upright four‐junction GaInP/GaAs/GaInNAsSb/GaInNAsSb solar cells grown by molecular beam epitaxy on p‐GaAs substrates with bandgaps of 1.88, 1.42, 1.17, and 0.93 eV, respectively. The four‐junction cell exhibited an efficiency of ~39% at 560‐sun illumination while showing good electrical performance even up to 1000 suns. As a first step to further improve the efficiency toward 50% level, we demonstrate AlGaInP (>2 eV) and GaInNAsSb (<0.8 eV) subcells. We prove that AlGaInP cells with 0.1 Al composition would exhibit current‐matching condition when being incorporated in a five‐junction architecture together with two GaInNAsSb bottom and AlGaAs top junctions. Furthermore, current matching required for a six‐junction tandem architecture is achieved for an Al composition of 0.26. Overall, the results open a practical path toward fabrication of lattice‐matched solar cells with more than four junctions.