ZnO-based interdigitated MSM and MISIM ultraviolet photodetectors

Abstract

The paper reports the fabrication and characterization of ZnO-based interdigitated metal–semiconductor–metal (MSM) and metal–insulator–semiconductor–insulator–metal (MISIM) ultraviolet photodetectors. The ZnO thin film was grown on a p-type Si ⟨1 0 0⟩ substrate by the sol–gel technique. With applied voltage in the range from −3 to 3 V we estimated the contrast ratio, responsivity, detectivity and quantum efficiency of the photodetectors for an incident optical power of 0.1 mW at 365 nm ultraviolet wavelength. The I–V characteristics were studied and the parameters such as ideality factor, leakage current and barrier height were extracted from the measured data. For Au/Cr/SiO2/ZnO/SiO2/Al (MISIM) structure the product (mχ) of the tunnelling effective electron mass (m) and the mean tunnelling barrier height (χ) was also extracted.

Ultraviolet Photodetection Properties of ZnO/Si Heterojunction Diodes Fabricated by ALD Technique Without Using a Buffer Layer

“…The responsivity of the photodiode at -2 V bias voltage under the UV illumination at 365 nm with incident optical power of 650 µW is estimated to be ~0.075 A/W which is in good agreement with that reported by Luo et al for their ZnO nanowire/Si heterojunction photodiodes prepared by vapour transport method [9]. The optical to electrical conversion efficiency of the photodiode, termed as the external quantum efficiency (EQE) η is defined by [8]:…”

“…the reverse saturation current 0 I ) is ~44.8 nA and current under UV illumination at 365 nm is ~48.5 µA respectively at 2 V reverse bias. The resultant contrast ratio which is defined as the ratio of photocurrent and dark current [8] is measured as ~1115 which appears to be much larger than the reported data [12]. The reason behind this huge enhancement of photocurrent is investigated further.…”

“…By using the conventional method [8], the parameters n and 0 I are estimated from the ln(I) versus V plot at room temperature as ~2.72 and ~4.15×10 The key parameters of the device clarify that the interface quality of the n-ZnO thin film /p-Si heterojunction is comparatively better than the heterojunction photodiode reported by Yakuphanoglu et al [12] by using sol-gel method without using a buffer layer.…”

“…As an alternative, many researchers are trying to explore the low-cost, environment friendly and wide band gap (~3.34 eV) zinc oxide (ZnO) material with large exciton energy (~60 meV larger than GaN ~25 meV) for the UV detection applications [5,6]. They have shown their interest to investigate ZnO based UV photodetectors with different configurations such as Schottky diode [5,6], MSM (metal-semiconductor-metal) [3,7,8], MISM (metalinsulator-semiconductor-metal) [2,8] and p-n heterojunction [9][10][11][12][13] photodiode structures. Since, ZnO is an intrinsically n-type semiconductor, the fabrication of a stable and controllable p-type ZnO thin film is very difficult [11].…”

“…without using any seed layer) by using the ALD technique which is commonly recommended for the conformal deposition of high quality ZnO thin films with precise thickness and composition control at low deposition temperature [16,17,19]. Although, the ALD grown n-ZnO film has already been used in the metal/nZnO/metal structure (MSM type) based UV detectors with palladium Schottky contacts [8], but, to the best of our available knowledge, the ALD grown ZnO thin film for the fabrication of n-ZnO /p-Si heterojunction photodiode is believed to be considered for the first time in this paper.…”