Arrays of III–V direct-bandgap semiconductor nanopillars represent promising photovoltaic candidates due to their inherent high optical absorption coefficients and minimized reflection arising from light trapping, efficient charge collection in the radial direction and the ability to synthesize them on low-cost platforms. However, the increased surface area results in surface states that hamper the power conversion efficiency. Here, we report the first demonstration of GaAs nanopillar-array photovoltaics employing epitaxial passivation with air mass 1.5 global power conversion efficiencies of 6.63%. High-bandgap epitaxial InGaP shells are grown in situ and cap the radial p–n junctions to alleviate surface-state effects. Under light, the photovoltaic devices exhibit open-circuit voltages of 0.44 V, short-circuit current densities of 24.3 mA cm−2 and fill factors of 62% with high external quantum efficiencies >70% across the spectral regime of interest. A novel titanium/indium tin oxide annealed alloy is exploited as transparent ohmic anode.

We demonstrate nanopillar-(NP) based plasmon-enhanced photodetectors (NP-PEPDs) operating in the near-infrared spectral regime. A novel fabrication technique produces subwavelength elongated nanoholes in a metal surface self-aligned to patterned NP arrays that acts as a 2D plasmonic crystal. Surface plasmon Polariton Bloch waves (SPP-BWs) are excited by the metal nanohole array resulting in electric field intensity "hot spots" in the NP. The NP periodicity determines the peak responsivity wavelength while the nanohole asymmetry produces polarization-dependent coupling of the SPP-BW modes. Resulting photodetectors have 0.28 A/W responsivity peaked at 1100 nm at a reverse bias of -5 V. Designs for further increasing the optical coupling efficiency into the nanopillar are explored. This technology has potential applications for plasmonically enhanced focal plane arrays and plasmonic photovoltaics.

InAs1-xSbx nanowires have recently attracted interest for infrared sensing applications due to the small bandgap and high thermal conductivity. However, previous reports on nanowire-based infrared sensors required low operating temperatures in order to mitigate the high dark current and have shown poor sensitivities resulting from reduced light coupling efficiency beyond the diffraction limit. Here, InAsSb nanopillar photodiodes with high quantum efficiency are achieved by partially coating the nanopillar with metal that excites localized surface plasmon resonances, leading to quantum efficiencies of ∼29% at 2390 nm. These high quantum efficiency nanopillar photodiodes, with 180 nm diameters and 1000 nm heights, allow operation at temperatures as high as 220 K and exhibit a detection wavelength up to 3000 nm, well beyond the diffraction limit. The InAsSb nanopillars are grown on low cost GaAs (111)B substrates using an InAs buffer layer, making our device architecture a promising path toward low-cost infrared focal plane arrays with high operating temperature.

We demonstrate a nanopillar (NP) device structure for implementing plasmonically enhanced avalanche photodetector arrays with thin avalanche volumes (∼ 310 nm × 150 nm × 150 nm). A localized 3D electric field due to a core-shell PN junction in a NP acts as a multiplication region, while efficient light absorption takes place via surface plasmon polariton Bloch wave (SPP-BW) modes due to a self-aligned metal nanohole lattice. Avalanche gains of ∼216 at 730 nm at -12 V are obtained. We show through capacitance-voltage characterization, temperature-dependent breakdown measurements, and detailed device modeling that the avalanche region is on the order of the ionization path length, such that dead-space effects become significant. This work presents a clear path toward engineering dead space effects in thin 3D-confined multiplication regions for high performance avalanche detectors for applications in telecommunications, sensing and single photon detection.