Effect of Li doping in NiO thin films on its transparent and conducting properties and its application in heteroepitaxial p-n junctions

Abstract

Li doped NiO (LixNi1−xO) thin films were epitaxially grown along [111] orientation on c-sapphire by pulsed laser deposition. The structural, electrical, and optical properties of the films were investigated using x-ray diffraction, four probe technique, and UV-visible spectra, respectively. The epitaxial growth of [111] Li doped NiO on [0001] sapphire was determined by using high resolution x-ray Φ scan. Effects of the deposition condition and Li doping concentration variations on the electrical and optical properties of Li doped NiO films were also investigated. The analysis of the resistivity data show that doped Li ions occupy the substitutional sites in the films, enhancing the p-type conductivity. The minimum resistivity of 0.15 Ω cm was obtained for Li0.07Ni0.93O film. The activation energy of Li doped NiO films were estimated to be in the range of 0.11–0.14 eV. Based upon these values, a possible electrical transport mechanism is discussed. A p-n heterojunction has also been fabricated for the optimized p-Li doped NiO with n-ZnO. The insertion of i-MgZnO between the p and n layer led to improved current-voltage characteristics due to reduced leakage current. In the diode architecture, a heteroepitaxial relationship of [111]NiO‖[0001]MgZnO‖[0001]ZnO‖[0001]GZO‖[0001]Al2O3 among the layers was obtained. The p-i-n heterojunction showed good rectification behavior with turn on voltage of 2.8 V and breakdown voltage of 8.0 V.

Lattice spacings and domain sizes of room-temperature epitaxial Li x Ni 1−x O (0 ≤ x ≤ 0.48) thin films grown on ultra-smooth sapphire substrates

“…This is due to two types of terraces of the 0.2-nm-high stepped sapphire (0 0 0 1) substrate with the three-fold symmetry [16]. consistent with that reported in [11,17]. Fig.…”

“…It is noteworthy that the value of the (1 1 1) lattice spacing of Li 0.48 Ni 0.52 O thin film is most close to that of bulk NiO cubic structure. The decrease of the unit cell size with increasing a Li amount might be partly due to the difference in ionic radius between Ni 2+ and Ni 3+ ions [17,18].…”

Cyclic voltammetry on sputter-deposited films of electrochromic Ni oxide: Power-law decay of the charge density exchange

“…The details differ, however, and the main diffraction peaks corresponding to the (111) and (220) lattice planes are shifted slightly towards higher diffraction angles for colored as well as bleached films, which implies a shrinkage of the separation between these lattice planes compared to their separation in asdeposited films. This effect is connected with the irreversible Li insertion and has been noted also in earlier work on lithiated Ni oxide [52][53][54]89]. It is associated with compressive stress whose origin is not known.…”

Fabrication of visible‐light transparent solar cells composed of NiO/NixZn1‐xO/ZnO heterostructures

“…In fact, NiO has attracted attention because Li- [4,5], Na- [6], K- [7], Cu- [8], N- [9], or unintentionally doped NiO shows p-type conductivity [10][11][12]. Therefore, visible-light-transparent diodes [13][14][15], ultraviolet (UV)/visible light-emitting diodes [16], and UV detectors [17] have been fabricated by using p-type NiO and n-type oxide semiconductors (e.g., ZnO). Recently, NiO has also been used in visible-light transparent solar cells, which are attractive because of their optical transparency that allows greater flexibility in choosing the installation location.…”