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Title: UV light induced insulator-metal transition in ultra-thin ZnO/TiO{sub x} stacked layer grown by atomic layer deposition

Abstract

In the present study, atomic layer deposition has been used to grow a series of Ti incorporated ZnO thin films by vertically stacking different numbers (n = 1–7) of ZnO/TiO{sub x} layers on (0001) sapphire substrates. The effects of defect states mediated chemisorption of O{sub 2} and/OH groups on the electrical properties of these films have been investigated by illuminating the samples under UV light inside a high vacuum optical cryostat. The ultra-thin film having one stacked layer (n = 1) did not show any change in its electrical resistance upon UV light exposure. On the contrary, marginal drop in the electrical resistivity was measured for the samples with n ≥ 3. Most surprisingly, the sample with n = 2 (thickness ∼ 12 nm) showed an insulator to metal transition upon UV light exposure. The temperature dependent electrical resistivity measurement on the as grown film (n = 2) showed insulating behaviour, i.e., diverging resistivity on extrapolation to T→ 0 K. However, upon UV light exposure, it transformed to a metallic state, i.e., finite resistivity at T → 0 K. Such an insulator-metal transition plausibly arises due to the de-trapping of conduction electrons from the surface defect sites which resulted in an upward shift of the Fermi level above the mobility edge. The low-temperature electron transportmore » properties on the insulating film (n = 2) were investigated by a combined study of zero field electrical resistivity ρ(T) and magnetoresistance (MR) measurements. The observed negative MR was found to be in good agreement with the magnetic field induced suppression of quantum interference between forward-going paths of tunnelling electrons. Both ρ(T) and MR measurements provided strong evidence for the Efros-Shklovskii type variable range hopping conduction in the low-temperature (≤40 K) regime. Such studies on electron transport in ultra-thin n-type doped ZnO films are crucial to achieve optimum functionality with long term reliability of ZnO based transparent conducting oxides.« less

Authors:
;  [1]
  1. Laser Materials Processing Division, Raja Ramanna Centre for Advanced Technology, Indore 452 013 (India)
Publication Date:
OSTI Identifier:
22598890
Resource Type:
Journal Article
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 120; Journal Issue: 8; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-8979
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CHEMISORPTION; CRYOSTATS; DEPOSITION; DOPED MATERIALS; ELECTRON TEMPERATURE; ELECTRONS; EXTRAPOLATION; FERMI LEVEL; LAYERS; MAGNETIC FIELDS; MAGNETORESISTANCE; METALS; SAPPHIRE; SUBSTRATES; TEMPERATURE DEPENDENCE; THIN FILMS; TITANIUM OXIDES; TUNNEL EFFECT; ULTRAVIOLET RADIATION; ZINC OXIDES

Citation Formats

Saha, D., E-mail: sahaphys@gmail.com, E-mail: pmisra@rrcat.gov.in, Misra, P., E-mail: sahaphys@gmail.com, E-mail: pmisra@rrcat.gov.in, Joshi, M. P., and Kukreja, L. M. UV light induced insulator-metal transition in ultra-thin ZnO/TiO{sub x} stacked layer grown by atomic layer deposition. United States: N. p., 2016. Web. doi:10.1063/1.4961415.
Saha, D., E-mail: sahaphys@gmail.com, E-mail: pmisra@rrcat.gov.in, Misra, P., E-mail: sahaphys@gmail.com, E-mail: pmisra@rrcat.gov.in, Joshi, M. P., & Kukreja, L. M. UV light induced insulator-metal transition in ultra-thin ZnO/TiO{sub x} stacked layer grown by atomic layer deposition. United States. doi:10.1063/1.4961415.
Saha, D., E-mail: sahaphys@gmail.com, E-mail: pmisra@rrcat.gov.in, Misra, P., E-mail: sahaphys@gmail.com, E-mail: pmisra@rrcat.gov.in, Joshi, M. P., and Kukreja, L. M. Sun . "UV light induced insulator-metal transition in ultra-thin ZnO/TiO{sub x} stacked layer grown by atomic layer deposition". United States. doi:10.1063/1.4961415.
@article{osti_22598890,
title = {UV light induced insulator-metal transition in ultra-thin ZnO/TiO{sub x} stacked layer grown by atomic layer deposition},
author = {Saha, D., E-mail: sahaphys@gmail.com, E-mail: pmisra@rrcat.gov.in and Misra, P., E-mail: sahaphys@gmail.com, E-mail: pmisra@rrcat.gov.in and Joshi, M. P. and Kukreja, L. M.},
abstractNote = {In the present study, atomic layer deposition has been used to grow a series of Ti incorporated ZnO thin films by vertically stacking different numbers (n = 1–7) of ZnO/TiO{sub x} layers on (0001) sapphire substrates. The effects of defect states mediated chemisorption of O{sub 2} and/OH groups on the electrical properties of these films have been investigated by illuminating the samples under UV light inside a high vacuum optical cryostat. The ultra-thin film having one stacked layer (n = 1) did not show any change in its electrical resistance upon UV light exposure. On the contrary, marginal drop in the electrical resistivity was measured for the samples with n ≥ 3. Most surprisingly, the sample with n = 2 (thickness ∼ 12 nm) showed an insulator to metal transition upon UV light exposure. The temperature dependent electrical resistivity measurement on the as grown film (n = 2) showed insulating behaviour, i.e., diverging resistivity on extrapolation to T→ 0 K. However, upon UV light exposure, it transformed to a metallic state, i.e., finite resistivity at T → 0 K. Such an insulator-metal transition plausibly arises due to the de-trapping of conduction electrons from the surface defect sites which resulted in an upward shift of the Fermi level above the mobility edge. The low-temperature electron transport properties on the insulating film (n = 2) were investigated by a combined study of zero field electrical resistivity ρ(T) and magnetoresistance (MR) measurements. The observed negative MR was found to be in good agreement with the magnetic field induced suppression of quantum interference between forward-going paths of tunnelling electrons. Both ρ(T) and MR measurements provided strong evidence for the Efros-Shklovskii type variable range hopping conduction in the low-temperature (≤40 K) regime. Such studies on electron transport in ultra-thin n-type doped ZnO films are crucial to achieve optimum functionality with long term reliability of ZnO based transparent conducting oxides.},
doi = {10.1063/1.4961415},
journal = {Journal of Applied Physics},
issn = {0021-8979},
number = 8,
volume = 120,
place = {United States},
year = {2016},
month = {8}
}