Photonic power converters (PPCs) are a class of photovoltaic devices designed for efficient conversion of monochromatic (laser or LED) light to electricity. These devices are composed of multiple p-n junction diodes arranged in a tandem configuration and connected in series. They have reached high energy conversion efficiencies (70%) and areal power densities of 100 W/cm$^{2}$. When these devices are illuminated with a high-efficiency diode laser they can provide isolated DC-DC conversion from the laser voltage (< 2.3 V) to the open-circuit voltage of the PPC (1.2 to 23 V) with low capacitance and low conducted electromagnetic interference compared to conventional switching power converters. The voltage conversion ratio is controlled by varying the number of p-n junctions in the PPC from 1 to 20 in demonstrated designs. In this article we demonstrate the use of photonic power conversion within two new applications. Firstly, the laser/PPC unit is applied as a linear photonic boost converter, producing a regulated 12V output stepped-up from a 3.3V input to the control board. Output ripple is negligible as compared with a switching boost converter of similar size. Efficiency of this linear, regulated DC/DC conversion system was 12.7%, compared with a 77.6% reference switch-mode converter. Power density was 0.18 W/cm$^{3}$, compared with 1.5 W/cm$^{3}$ for the reference. Relative to switch-mode power conversion, the photonic technology has lower efficiency and lower power density, but superior isolation and rejection of ripple and EMI. Both technologies are highly scalable. For the second application, the same unit is applied to power a 650V SiC MOSFET gate driver requiring high galvanic isolation, demonstrating a 20 dB reduction in conducted-current electromagnetic interference from the power circuit into the lowvoltage control systems.

Laterally-coupled distributed feedback (LC-DFB) lasers use a lithographic fabrication step to define the distributed feedback grating, avoiding subsequent regrowth. Using higher order gratings can enhance the lithographic tolerance for lower resolution patterning, yielding lasers more amenable to fabrication. We show that LC-DFB lasers with higher order gratings, although requiring a higher threshold gain than those of first-order, provide a degree of longitudinal mode discrimination. Incorporating radiating partial waves, we have calculated modified coupled-mode coefficients for various duty cycles, grating orders, and grating geometries using a two-dimensional finite-element method. The modified coupled-mode equations were solved with and without a lambda/4 phase shift. The phase shift, while beneficial for first-order gratings, was found to generally diminish laser performance for lasers with higher order gratings.

Micro‐concentrator photovoltaic (CPV), incorporating micro‐scale solar cells within concentrator photovoltaic modules, promises an inexpensive and highly efficient technology that can mitigate the drawbacks that impede standard CPV, such as resistive power losses. In this paper, we fabricate micro‐scale multijunction solar cells designed for micro‐CPV applications. A generic process flow, including plasma etching steps, was developed for the fabrication of complete InGaP/InGaAs/Ge microcells with rectangular, circular, and hexagonal active areas down to 0.089 mm² (0.068‐mm² mesa). Large cells (>1 mm²) demonstrate good electrical performance under one sun AM1.5D illumination, but a degradation in the open‐circuit voltage (V_OC) is observed on the smallest cells. This effect is attributed to perimeter recombination for which a passivation effect by the antireflective coating partially recovers the V_OC. The V_OC penalty for small cells is also reduced under high‐intensity illumination, from 3.8% under sun to 1.0% at 974 suns. High intensity illumination yields an efficiency of 33.8% under 584 suns for a 0.25‐mm² and microcells are expected to show higher efficiency than standard cells under very high concentration.

Intermediate band solar cells hold the promise of ultrahigh power conversion efficiencies using a single semiconductor junction. Many current implementations use materials with bandgaps too small to achieve maximum efficiency or use cost-prohibitive substrates. Here we demonstrate a material system for intermediate band solar cells using InGaN/GaN quantum-dot-in-nanowire heterostructures grown directly on silicon to provide a lower cost, large-bandgap intermediate band solar cell platform. We demonstrate sequential two-photon current generation with sub-bandgap photons, the hallmark of intermediate band solar cell operation, through vertically stacked quantum dots in the nanowires. Near-infrared light biasing with an 850 nm laser intensity up to 200 W/cm² increases the photocurrent above and below the bandgap by up to 19% at 78 K, and 44% at room temperature. The nanostructured III-nitride strategy provides a route towards realistic room temperature intermediate band solar cells while leveraging the cost benefits of silicon substrates.

Waste heat is a free and abundant energy source, with 15% of global total energy use existing as waste heat above 600 K. For 600–900 K temperature range, near-field thermophotovoltaics (NFTPVs) are theorized to be the most effective technology to recycle waste heat into electrical power. However, to date, experimental efficiencies have not exceeded 1.5%. In this work, we optimize the efficiency of three modeled InAs/InAsSbP-based room-temperature NFTPV devices positioned 0.1 μm from a 750 K p-doped Si radiator. We couple a one-dimensional fluctuational electrodynamics model for the near field optics to a two-dimensional drift-diffusion model, which we validated by reproducing measured dark current–voltage curves of two previously published InAs and InAsSbP devices. The optimized devices show four to six times higher above-bandgap energy transfer compared to the blackbody radiative limit, yielding enhanced power density, while simultaneously lowering parasitic sub-bandgap energy transfer by factors of 0.68–0.85. Substituting InAs front- and back-surface field layers with InAsSbP show 1.5- and 1.4-times higher efficiency and power output, respectively, from lowered parasitic diffusion currents. Of our three optimized designs, the best performing device has a double heterostructure with an n–i–p doping order from front to back. For radiator-thermophotovoltaic gaps of 0.01–10 μm and radiators within 600–900 K, this device has a maximum efficiency of 14.2% and a maximum power output of 1.55 W/cm², both at 900 K. Within 600–900 K, the efficiency is always higher with near- vs far-field illumination; we calculate up to 3.7- and 107-times higher efficiency and power output, respectively, using near-field heat transfer.

InAlGaAs tunnel diodes, lattice-matched to InP and grown by molecular beam epitaxy, are demonstrated with peak tunneling current densities exceeding 1200 A/cm². This was achieved by a 20 °C reduction in growth temperature for the p-type tunnel diode layers, resulting in up to two orders of magnitude improvement in the peak tunneling current density. Secondary ion mass spectrometry measurements reveal that the lower growth temperature reduces unwanted segregation of p-type Be dopants, improving dopant incorporation within the active tunnel diode layers. The diodes are transparent to wavelengths above 1000 nm and are compatible with the bottom junctions of InP-based multi-junction solar cells and with InP-based photonic power converters operating in the telecommunication O- and C-bands. When incorporated into a dual-junction photonic power converter test structure, measurements under 1319-nm laser illumination demonstrate integrated tunnel diode operation, enabling a halving of the short-circuit current and doubling of the open-circuit voltage as compared to a single junction reference device.