We report the fabrication of GaN nanopillar arrays with good structural uniformity using the top-down approach. The photoluminescence intensity from the nanopillar arrays is enhanced compared to the epilayer. We use finite difference time domain simulations to show that the enhancement in photoluminescence intensity from the nanopillar arrays is a result of anti-reflection properties of the arrays that result in enhanced light absorption and increase light extraction efficiency compared to the epilayer. The measured quantum efficiency of the nanopillars is comparable to that of an epitaxially grown GaN epilayer.

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The effect of light soaking (LS) is studied in hydrogenated amorphous silicon (a-Si:H) containing different amounts of nanocrystals, prepared by varying the deposition conditions in a plasma enhanced chemical vapor deposition (PECVD) system. We find that the presence of nanocrystals (nc-Si) stabilizes the a-Si:H against LS. The long range potential fluctuations (LRPF) are measured and we find that they become smaller as the fraction of nanocrystals (χ) in the films increases. Raman spectra show a peak at 490 cm−1, which is taken to be the result of Intermediate Range Order (IRO) in the films. This IRO peak appears just when the hydrogen dilution is sufficiently high for the crystallization to begin, and increases with increasing hydrogen dilution as the crystallization increases. In contrast LRPF have maximum width when χ is zero and it decreases as χ increases. Further, the degradation upon LS is negligible when χ > 25%. We suggest an alternative mechanism for the improved stability, in which the photogenerated carriers moving under the influence of the long range potential fluctuations have a propensity to go to nc-Si, and recombine in that region.

Arrays of n-CdS nanowires were investigated as replacement for the planar n-CdS film; the latter is presently used as a window layer in important photovoltaic devices like CdS-CdTe and CdS-CIGS. CdS nanowire arrays continued to exhibit substantial transmission even when the wavelength of incident radiation was well below 512 nm, which is the wavelength corresponding to the energy band gap of single crystal CdS. Theoretical calculation involving the number of excess photons transmitted through the CdS nanowire window layer indicated a potential enhancement in photocurrent by as much as 38% over the planar CdS film window layer device. Next, Au/CdS Schottky diodes were formed by depositing thin films of gold on the nanowire arrays. Analysis of the currentvoltage characteristics of these Schottky diodes showed smaller diode ideality factors and higher carrier concentrations in devices with CdS nanowires than in devices with planar CdS films; these are desirable junction characteristics when the designer is trying to maximize the open circuit voltage and the power output.