Persistent Photoconductivity of Solution-Grown ZnO–Based UV Detectors

Abstract

Based on space-confining effect, ZnO nanowire-based photodetectors with different diameters have been fabricated onto interdigitated electrodes with varied seed density in solution process. It is found that the rise and recovery time are determined by the diameter of nanowires due to the fact that the photogenerated carriers recombined swiftly with the increasing amount of surface states. After modifying the ZnO NWs in a hydrothermal process the response time decreases obviously, which is resulted from suppressed oxygen vacancy. A possible model about the origin of the persistent photoconductivity is proposed. The persistent photoconductivity is considered to result from the shallow donor state of neutral oxygen vacancy which is developed from electron transit to singly ionized oxygen vacancy. An electron prefers to be captured by recombination center present in middle of the forbidden band while holes are migrating to surface of nanowire caused by band bending near surface.

Ultrahigh-Responsivity, Rapid-Recovery, Solar-Blind Photodetector Based on Highly Nonstoichiometric Amorphous Gallium Oxide

“…46,47 For example, the recombination of photogenerated carriers in ZnO nanowires was dramatically accelerated as the diameters of the nanowires decreased; this behavior was attributed to the appearance of more surface states with larger surface-to-volume ratios, and accordingly, enhanced surface recombination. 48,49 In this work, a high density of defects, for example, structural disorders 50 and oxygen vacancies, 47 as observed in the a-GaO x thin film, facilitated the recombination of nonequilibrium carriers (process 8 in Figure 7b). 51 More importantly, the assputtered film possessed a rough and porous surface and, thus, a large surface-to-volume ratio, which might further enhance the surface recombination and shorten the carrier lifetime.…”

“…In fact, deep-level defects can function not only as carrier traps, but also as effective recombination centers . Moreover, surface, rather than bulk, recombination is often the dominant mechanism during the annihilation of nonequilibrium carriers because of the much higher density of defect states, including some that are unique to the surface. , For example, the recombination of photogenerated carriers in ZnO nanowires was dramatically accelerated as the diameters of the nanowires decreased; this behavior was attributed to the appearance of more surface states with larger surface-to-volume ratios, and accordingly, enhanced surface recombination. , In this work, a high density of defects, for example, structural disorders and oxygen vacancies, as observed in the a-GaO x thin film, facilitated the recombination of nonequilibrium carriers (process 8 in Figure b) . More importantly, the as-sputtered film possessed a rough and porous surface and, thus, a large surface-to-volume ratio, which might further enhance the surface recombination and shorten the carrier lifetime.…”

High rate (~7 nm/s), atmospheric pressure deposition of ZnO front electrode for Cu(In,Ga)Se2 thin‐film solar cells with efficiency beyond 15%

“…As shown in Figure , the sheet resistance decreases sharply, from ~2 MΩ/sq to 20 Ω/sq in 4 min, when ZnO films are exposed to an iron lamp which emits a radiation in the range from 302 to 527 nm. The resistance of ZnO thin films is known to decrease when exposed to UV radiation . A UV optical filter has been used to absorb the near‐UV radiation (i.e., from 302 to 380 nm) emitted by the lamp.…”

8.4L: Late‐News Paper: Electrical Properties of a‐IGZO Films Depending on Trap States

“…It indicates that the slow relaxation is attributed to the slow neutralization of the ionized oxygen vacancies. Moreover, a recent study [13] reported that the PPC observed in solutionprocessed ZnO was attributed to the shallow donor state of neutral oxygen vacancy which is developed from electron transit to singly ionized oxygen vacancy. Even there exists several explanations, it is consistent that oxygen vacancy is related to the self-doping and…”