Anomalous time variation of photocurrent in GaN during photoelectrochemical reaction for H₂ gas generation in NaOH aqueous solution

Abstract

We investigated the time variation of photocurrent in GaN during photoelectrochemical reaction without bias. The time variation of photocurrent showed a “w”‐shape behaviour. The surface morphology and photoluminescence spectra of GaN after the reaction with different treatment times were also evaluated in order to clarify the “w”‐shape time variation. The roughened and chemically changed surface of the GaN caused the “w”‐shape time variation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Time dependence of water‐reducing photocurrent with change of the characteristics of n‐type GaN photo‐illuminated working electrodes

“…The surfaces of undoped GaN and Si-doped GaN with the donor concentration of 1.3 × 10 16 cm -3 were almost smooth but those of the other Si-doped samples were orange peal like. These surface changes of the higher donor concentration samples were similar to the previous results [4]. For the sample with the donor concentration with 1.3 × 10 16 cm -3 , the surface near the contact electrode was not smooth compared to the other area as shown in Fig.…”

“…Photocurrent density increasing after the decreasing was observed within 200 min from the photoillumination started. The details of the time dependent curves were discussed elsewhere [4]. For Si-doped GaN, the peak photocurrent density with the smaller FWHM of XRC (0.70 mA/cm 2 at 69 min) was higher than that with the larger FWHM of XRC (0.49 mA/cm 2 at 39 min).…”

“…The photocurrent time dependence is accelerated by the increasing of illuminated light intensity and is changed by applied bias [3]. Change of the surface index from (0001) due to the surface photocorrosion was clarified to cause the decreasing of photocurrent [4]. These results suggest that the changing triggers are defect formations at the semiconductor surface.…”

“…The donor concentrations of Sidoped samples were from 10 16 to 10 18 cm -3 and that for undoped GaN was below 10 16 cm -3 . The Si was doped by the additional flow of SiH 4 . The full-widths at half-maximum (FWHM) of x-ray rocking curve (ω-scan, XRC) of (0002) were around 200 to 300 arcsec for all samples.…”

“…Suppression of surface morphology change has been expected when the stable photocurrent of n-type GaN is achieved [4]. The photographs of the GaN surfaces after photoelectrochemical reaction of about 650 min taken by optical microscope are shown in Fig.…”