ANNEALING TIME EFFECT ON NANOSTRUCTURED n-ZnO/p-Si HETEROJUNCTION PHOTODETECTOR PERFORMANCE

Abstract

In this work, n-ZnO/p-Si heterojunction photodetectors were prepared by drop casting of ZnO nanoparticles (NPs) on single crystal p-type silicon substrates, followed by (15-60) min; stepannealing at 600 C. Structural, electrical, and optical properties of the ZnO NPs¯lms deposited on quartz substrates were studied as a function of annealing time. X-ray di®raction studies showed a polycrystalline, hexagonal wurtizte nanostructured ZnO with preferential orientation along the (100) plane. Atomic force microscopy measurements showed an average ZnO grain size within the range of 75.9 nm-99.9 nm with a corresponding root mean square (RMS) surface roughness between 0.51 nm-2.16 nm. Dark and under illumination current-voltage (I-V) characteristics of the n-ZnO/ p-Si heterojunction photodetectors showed an improving recti¯cation ratio and a decreasing saturation current at longer annealing time with an ideality factor of 3 obtained at 60 min annealing time. Capacitance-voltage (C-V ) characteristics of heterojunctions were investigated in order to estimate the built-in-voltage and junction type. The photodetectors, fabricated at optimum annealing time, exhibited good linearity characteristics. Maximum sensitivity was obtained when ZnO/Si heterojunctions were annealed at 60 min. Two peaks of response, located at 650 nm and 850 nm, were observed with sensitivities of 0.12-0.19 A/W and 0.18-0.39 A/W, respectively. Detectivity of the photodetectors as function of annealing time was estimated.

Annealing dependence on flexible p-CuGaO2/n-ZnO heterojunction diode deposited by RF sputtering method

“…The effect of annealing duration on the ideality factor calculated forward bias I-V characteristic was observed is in the range of those reported for ITO/ poly(3,4,ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/poly(2-methoxy-5-(2-ethlhexyloxy))-1,4-phenylenevinylene)(MEH-PPV)/Alq3/Lif/Au Schottky diode [24], and comparable to that those reported for ITO/MEH-PPV/A21 [28]. Large values of ideality factor were obtained due to the presence of recombination in the junction deposition or at junction interface [25], besides some structural defects and lattice mismatch between ZnO and CuGaO2 [19]. The improvement of the device performance is attributed to the smoother surface [26].…”

“…An obvious increment in the intensity of ZnO (002) peak noticed from 10, 20 and 30 minutes annealing duration indicating better crystallinity. An increase in the diffraction intensity observed with long annealing duration due to the enhanced films quality [19]. However, the intensity of ZnO (002) peak drops at 40 minutes and continues to decrease in longer annealing duration of 60 minutes indicate the films crystallinity deteriorates.…”

Effect of annealing temperature on structural, electrical, and UV sensingcharacteristics of n-ZnO/p-Si heterojunction photodiodes

“…[26]. Higher annealing temperatures improve the grain growth, which may also increase the porosity of the films [27]. Although the RMS values are higher than an ideal smooth surface (a few angstroms), they are still in a comparable range for ZnO-based devices used in various applications [2,28,29].…”

“…The threshold voltage approaches 0 V and the reverse bias current increases after 350 • C annealing. It has been reported that mobility increases with increasing grain size [27], and the presence of localized defect sites may act as a leak path. Hence, the rise in the reverse current (dark current) is associated with the crystallization of the ZnO layer.…”

Substrate Effects on Structural and Optical Properties of ZnO Thin Films Deposited by Chemical Spray Pyrolysis

“…Great unremtiting efforts have been made by the researches to synthesized ZnO thin films and nanosrtucture ZnO thin films [1][2][3][4][5][6]Zinc oxide (ZnO) is a wide band gap direct semiconductor having a band gap of (3.37) eV at room temperature. It also possesses large exciton-binding energy of 60 meV.…”