Effects of Annealing Environments on the Solution‐Grown, Aligned Aluminium‐Doped Zinc Oxide Nanorod‐Array‐Based Ultraviolet Photoconductive Sensor

Abstract

We have fabricated metal-semiconductor-metal- (MSM-) type ultraviolet (UV) photoconductive sensors using aluminium- (Al-) doped zinc oxide (ZnO) nanorod arrays that were annealed in different environments: air, oxygen, or a vacuum. The Al-doped ZnO nanorods had an average diameter of 60 nm with a thickness of approximately 600 nm that included the seed layer (with thickness~200 nm). Our results show that the vacuum-annealed nanorod-array-based UV photoconductive sensor has the highest photocurrent value of 2.43 × 10-4 A. The high photocurrent is due to the high concentration of zinc (Zn) interstitials in the vacuum-annealed nanorod arrays. In contrast, the oxygen-annealing process applied to the Al-doped ZnO nanorod arrays produced highly sensitive UV photoconductive sensors, in which the sensitivity reached 55.6, due to the surface properties of the oxygen-annealed nanorods, which have a higher affinity for oxygen adsorption than the other samples and were thereby capable of reducing the sensor’s dark current. In addition, the sensor fabricated using the oxygen-annealed nanorod arrays had the lowest rise and decay time constants. Our result shows that the annealing environment greatly affects the surface condition and properties of the Al-doped ZnO nanorod arrays, which influences the performance of the UV photoconductive sensors.

Microwave Synthesized ZnO Nanorod Arrays for UV Sensors: A Seed Layer Annealing Temperature Study

“…It is expected that the films annealed at higher temperatures presents a lower decay value due to the annihilation of surface trap [49]. …”

Effect of annealing process in tuning of defects in ZnO nanorods and their application in UV photodetectors

“…Considering the various restrictions of pure ZnO layer as an UV-detector such as low sensitivity and long time of response, various works have been carried out to optimize it as an efficient PD device [9,10]. Among the various modifications, the surface modification of ZnO nanostructures is accounted as an attractive way because of the diversity of fabrication methods for these nanostructures, their large surface availability, excellent optoelectronical, physical and chemical properties [11].…”

“…The concentration of defects in ZnO NR arrays undergoes a considerable change through annealing. On the other hands, the annealing, as a surface treatment process, can remove surface defects and contamination and modify surface absorption and desorption of oxygen molecules, thereby improving the surface condition of ZnO [11]. In this regard and since the UV photoconductivity is governed by the surface conditions of the NR arrays, effective annealing methods should be developed to reduce the number of defects and improve the surface quality of the prepared ZnO NR arrays.…”

“…Dhara et al [15] reported the major improvement in UV photosensitivity and faster photoresponse from vertically aligned ZnO nanowires by means of rapid thermal annealing at 700°C in Ar gas ambient. Also, Mamat et al [11] fabricated MSM (metal-semiconductor-metal) UV PDs using Al-doped ZnO NR arrays that were annealed at different atmospheres. They observed the higher photosensitivity for oxygen-annealed ZnO NRs.…”

Structural, Optical, Electrical, and Photoresponse Properties of Postannealed Sn‐Doped ZnO Nanorods

“…Photoresponse ( on / off ) increases as annealing temperature increases [52][53][54][55][56][57][58]. In ZnO-type materials, photoresponse is generally caused by oxygen desorption and adsorption process originating from either a bulk-or surface-related process [52,59,60].…”