Electrochemical properties of GaN nanowire electrodes—influence of doping and control by external bias

Abstract

We report on the electrochemical characteristics of GaN nanowire (NW) ensembles grown by plasma-assisted molecular beam epitaxy on Si111 substrates and on the influence of Si and Mg doping. The NW electrochemical properties in terms of surface capacitance (C(S)), surface resistance (R(S)) are extracted from electrochemical impedance spectra. While Mg doping of GaN NWs does not cause a significant variation of these quantities, an increase of the Si concentration leads to an increase of C(S) and a simultaneous decrease of R(S), indicating the presence of charge carriers in the NWs. According to the extracted values for R(S) and C(S) the NWs are classified into resistive and conductive. For conductive NWs charge transfer to a ferricyanide redox couple in the electrolyte is demonstrated and the ensemble average of the flatband voltage was determined. Variation of the lateral surface potential due to application of an external bias via the electrolyte is demonstrated.

Photoelectrochemical reduction of carbon dioxide using Ge doped GaN nanowire photoanodes

“…The growth conditions included a substrate temperature of 750 • C, nitrogen flow rate of 1.0 sccm, plasma forward power of 350 W, and Ga beam equivalent pressure of ∼6 × 10 −8 Torr. 13,36,37 The Ge effusion cell temperature was 1130 • C, which corresponds to Ge beam equivalent pressure (BEP) of ∼10 −11 Torr, which is similar the previous reports. 35,38 Due to the suitable atom size, Ge can be incorporated into GaN with less lattice distortion and can provide better nanowire morphology, compared to Si-doping.…”

“…However, the saturation photocurrent of undoped GaN nanowire photoanode was only ∼4.1 mA cm −2 at 1 V, indicating GaN nanowire with Ge doping is a promising photoanode material, due to enhanced conductivity. 32,37 The electrochemical impedance spectroscopy (EIS) also confirms that the conductivity of GaN nanowires is enhanced by Ge doping, which is in agreement with the carrier density increase of Ge doped GaN nanowires calculated from Mott-Schottky plot (not shown). The lack of obvious current saturation is likely related to the enhanced nonradiative recombination induced by Ge doping, due to the relatively high doping concentration.…”

Optical Analysis of Oxygen Self‐Diffusion in Ultrathin CeO2 Layers at Low Temperatures

“…MBE Growth of InGaN/GaN NWs : The InGaN/GaN nanowire core of the nanohybrid structure was prepared by a self‐assembled growth process using PAMBE and consists of a GaN base with a height of 390 nm (730 nm for Al 2 O 3 ‐coated samples) and an InGaN top part with a height of 350 nm (370 nm for Al 2 O 3 coated), the diameter varies between 50 and 100 nm over the substrate area. The position of InGaN PL emission indicates a band gap of ≈2.4 eV (Al 2 O 3 ‐coated: 2.25 eV) at room temperature.…”

Enhanced water splitting performance of GaN nanowires fabricated using anode aluminum oxide templates

“…GaN nanowires have strong potential applications in solar cells, nano-lasers, light emitting diodes (LED) and photoelectrochemical (PEC) water splitting. [4][5][6] Compared with thin lms and nano-sized powders, one-dimensional GaN nanowires exhibit a substantial enhancement in water splitting performance due to their high volume-to-surface ratio [7][8][9][10] and reduced distance for carriers to reach the electrolyte. 11,12 Furthermore, GaN has high chemical stability against the harsh PEC experiment conditions compared to other semiconductors.…”