Characteristics of Quantum Dots and Single-Phase p-CuInSe₂Nanowire Arrays Electrodeposited as Schottky Diodes with a Silver Contact

Abstract

CuInSe 2 nanowire (NW) arrays were prepared in a heated electrolyte (45 • C) through anodized aluminum oxide template-assisted pulse electrodeposition. After the CuInSe 2 NWs were as-grown, grazing incidence X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) revealed the recrystallization status of the CuInSe 2 NWs annealed at temperatures ranging from 250 • C to 550 • C. The results indicated that the NWs underwent a phase transformation from the (204/220) plane to the (112) plane. Additionally, the material particle size and quantum dots were measured using HRTEM and ultraviolet/visible spectroscopy. The particle size of the as-grown CuInSe 2 NWs ranged from 3.8 to 8 nm. The as-grown CuInSe 2 NWs exhibited a blue-shift in the material absorption band at 1100 and 1200 nm compared with those annealed at 550 • C. The results of scanning electron microscopy had a diameter and length of 80 nm and 2.2 μm, respectively. Mott-Schottky and ohmic contact plots revealed that the CuInSe 2 NWs were p-type semiconductors. Moreover, the different leakage current mechanisms of the nonideal Schottky diode were studied. Finally, near-ideal Schottky barrier diodes were obtained at an annealing temperature of 550 • C, and their work function was estimated to be in the range of 5.04-5. Copper indium selenide (CuInSe 2 ) is commonly used in photovoltaic applications because of its excellent properties, including the presence of a direct bandgap, a high absorption coefficient (> 10 5 cm −1 ), and high thermal and electrical stabilities. 1 According to the literature, thin-film CuInSe 2 solar cells fabricated through electrodeposition exhibit a conversion efficiency of approximately 8.7%, 2 and quaternary compound (CuIn 1-x Ga x Se 2 ) devices exhibit a conversion efficiency of 15.4%.3 However, the minority carrier lifetime of the thin-film structure is short because minority carriers have the longest mobility path (depending on material thickness). Onedimensional (1D) semiconductor nanostructures such as nanorods, nanowires (NWs), and nanotubes have been extensively investigated. These nanostructures show great promise to replace traditional thinfilm structures in optoelectronic and photovoltaic devices because of their unique optical and electronic properties, and because the geometry of 1D nanostructures can influence device performance.4-9 The 1D nanostructure can provide light absorption and a short carrier mobility path (radius of the NW) for minority carrier extraction efficiency. On the other hand, 1D nanostructure carrier lifetimes can be extended by improving scattering mechanisms and lattice vibration. The carrier mobility depends on the grain boundary, and this phenomenon implies that energy loss and the transfer of heat energy inside the material causes lattice vibration. It's worth mentioning, single-phase nanostructure can be easily achieved by control growth mechanisms and annealed through anodized aluminum oxide (AAO) templateassisted pulse electrodeposition. 10,11 Moreover, in the ternary...