Thin-Film III-V Devices for Low-Cost Detection and Energy Conversion

Abstract

III-V compound semiconductors are excellent candidates for high-performance optoelectronic devices due to their superior optical and electrical properties compared to elemental semiconductors. However, their expensive manufacturing cost compared to silicon-based optoelectronics often hinders their widespread use in general applications. Separating thin-film III-V epitaxial active layer from its growth substrate allows for potential reuse of the remaining substrate, which can reduce the substrate cost by a factor of total number of recycling. Moreover, thin-film structures allow fabrication of lightweight, flexible devices with improved photon recycling or light trapping, which can enhance device performance compared to conventional substrate devices. In this thesis, we introduce various applications using thin-film III-V photovoltaics (PV) and photodetectors. With non-destructive epitaxial lift-off (ND-ELO) technique, we demonstrate a thin-film GaAs PV cell fabrication and substrate recycling on a 4” GaAs wafer. We then integrate the thin-film PV cells with a low-cost mini parabolic concentrator array, which can potentially maintain a low profile compared to conventional bulky concentrated PV (CPV) modules. We also demonstrate a GaAs p-n junction focal plane array that resembles the shape and size of the human eye. Moreover, we deploy thin-film In0.53Ga0.47As (InGaAs) p-n junction thermophotovoltaic (TPV) device with Au surface back reflector and demonstrate a near-field heat transfer, with nearly an order of magnitude enhanced power conversion efficiency. xviii In addition, we estimate manufacturing cost of single junction GaAs PV cells with potential cost reduction scenarios such as improved throughput or increased number of substrate recycling. Our study reassures that substrate recycling plays a critical role in reducing the final cost. We also find that past claims that enhanced throughput can bring down the cost of GaAs PV to levels comparable to Si in terrestrial applications may be misleading. Finally, we demonstrate a Si TPV cell using air-bridge back surface reflector, with low series-resistance and high out-of-band reflectance (~97%). We estimate ~10% power conversion efficiency even under 1500K blackbody radiation, a source temperature where Si is considered impractical due to its high bandgap. We expect this advance could expedite the widespread of TPV system via reduced cost compared to conventional TPV materials such as InGaAs or InSb.