Photodetection by light-induced barrier modulation in Cu-diffused Au–CdS diodes

Abstract

Modified Schottky barriers of the type Au-CdS: Cu were prepared by diffusing Cu to a depth of O.l...{).2 JJ.m into single crystals of CdS, prior to evaporating rectifying Au contacts. The electronic and photoelectronic properties of these junctions are adequately described by a simple model in which the Cu acts as an ionized acceptor, resulting in a "humped" potential barrier between the Au and the bulk CdS. Hole trapping by the acceptors under band-gap illumination reduces their ionization and, consequently, the hump height. The forward current density in the dark and under illumination can be accurately described by a thermionic emission model as, where the hump potential V H (0) is light sensitive and where /3 (1 < /3 < 1.35) arises from a weak voltage dependence of the barrier height.Barrier height determinations, in the dark and under illumination with 5OOO-A light, by means of internal photoemission, thermal activation energy, and J -V measurements unequivocally show that under saturating light conditions the hump in the potential barrier is reduced by 0.23±0.03 V. This barrier mechanism of photoconductive response results in steady-state electron/photon gains in excess of 10 6 at light intensities lower that 5X lOll photons cm-2 sec-I, where response times exceed 1 sec.

Network-Enhanced Photoresponse Time of Ge Nanowire Photodetectors

“…It should be highlighted that this light-induced barrier height modulation is much faster than the trap discharging or oxygen diffusion processes (which usually accounts for photodetectors with Ohmic contact). For example, previous studies showed that the photocurrent response time for Au-CdS and Pt-ZnO Schottky barriers were typically below 1 s. However, the time required for trap discharging or oxygen diffusion was usually on the order of several minutes or upto hours ,,,− . Previously, Zhou et al reported that the reset time of ZnO NW photodetectors could be enhanced by intentionally deposited Schottky contact on single NW .…”

Metal‐p+‐n Enhanced Schottky Barrier Structures on (100) InP

“…Theoretical background.--Modified barrier heights due to shallow surface doping have been examined theoretically in considerable detail (9,(18)(19)(20)(21)(22)(23)(24)(25)(26) since the early 1970's. Various levels of approximation of carrier effects have been considered, including (i) the depletion approximation (9,(19)(20)(21)(22)(23)(24)(25), (ii) a limited inversion approximation that accounted for minority free-carriers outside the p* region (26), and (iii) numerical calculations, including both electron and hole free-carriers throughout the device structure (present work). In addition to approximations for the free-carrier densities, the effects associated with nonplanar doping profiles in the shallow p" layer have been considered by a number of authors (19,23).…”

“…Various levels of approximation of carrier effects have been considered, including (i) the depletion approximation (9,(19)(20)(21)(22)(23)(24)(25), (ii) a limited inversion approximation that accounted for minority free-carriers outside the p* region (26), and (iii) numerical calculations, including both electron and hole free-carriers throughout the device structure (present work). In addition to approximations for the free-carrier densities, the effects associated with nonplanar doping profiles in the shallow p" layer have been considered by a number of authors (19,23). A synopsis of these results pertinent to our data analysis follows.…”

“…In their analysis of Cu-diffused CdS diodes, Lubberts et al (19) outlined a scheme for determining K and t based on measurements of the barrier enhancement and the zero-bias capacitance. Our own measurements indicated that following Zn diffusion, the zero-bias capacitance showed strong frequency dispersion, making the determination of K and t highly uncertain.…”

Wide-bandgap Zn2GeO4 nanowire networks as efficient ultraviolet photodetectors with fast response and recovery time

“…The light induced barrier height modulation is typically much faster than the oxygen diffusion process ͑on the order of several minutes or hours͒. For example, it was shown previously that the photocurrent response time for bulk Au-CdS Schottky barrier was typically below 1 s. 18 Very recently, it was also reported that the recovery time of ZnO NW UV-sensors could be improved by focus-ion-beam deposited contacts with Schottky barrier. 8 In this letter, we suggest that the response and recovery time can be enhanced by using NW networks with NW-NW barrier dominated conductance.…”