157 ISSN 1068-3372, Journal of Contemporary Physics (Armenian Academy of Sciences), 2020, Vol. 55, No. 2, pp. 157–163. © Allerton Press, Inc., 2020. Russian Text © The Author(s), 2020, published in Izvestiya Natsional'noi Akademii Nauk Armenii, Fizika, 2020, Vol. 55, No. 2, pp. 228–239. Electric Noise in Field-Effect Transistors Based on ZnO:Li Films R. K. Hovsepyan a, b, *, N. R. Aghamalyan a, b , E. A. Kafadaryan a ,b , A. A. Arakelyan a, b , G. G. Mnatsakanyan a, b , and S. I. Petrosyan a, b a Russian–Armenian University, Yerevan, Armenia b Institute for Physical Research, NAS of Armenia, Ashtarak, Armenia *e-mail: ruben.ovsepyan@mail.ru Received November 22, 2019; revised January 14, 2020; accepted February 21, 2020 Abstract—The noise characteristics of field-effect transistors based on ZnO: Li films and obtained by the diffusion technology are studied. The results of an experimental study of the noise characteristics of the drain current are presented, namely, the Random Telegraph Signal and 1/f-noise. The spectral density of the drain current noises in the low-frequency range (10–5000 Hz) has a classical 1/f-depen- dence. It was found that at low concentrations of the acceptor impurity, 1/f noise is observed, and with an increase in the acceptor impurity concentration the Random Telegraph Signal prevails. Keywords: ZnO, field-effect transistor, hopping and drift conductivity, noise DOI: 10.3103/S1068337220020127 1. INTRODUCTION Transparent electronics has become a rapidly developing field of physics of semiconductors and mate- rials science, which allows to create a number of fundamentally new devices, for example, transparent dis- plays, transparent (invisible) security systems, etc. The main active elements of transparent electronics are transparent field-effect transistors and diodes [1, 2]. Many studies have been devoted to the production and investigation of such transistors, but the noise characteristics of transparent field-effect transistors have been little studied [3]. One of the fundamental factors limiting the performance of electronic struc- tures is the noise during signal transmission or information processing [4]. Decreasing in the noise level in micron and submicron metal–oxide–semiconductor (MOS) structures is an urgent task. In such MOS structures, due to the large surface-to-volume ratio, the noise characteristics, in particular low-frequency current noise, are more pronounced than in silicon semiconductor structures. Therefore, it is important to reduce the noise in such devices, at least to a level of the noise comparable to that in traditional semi- conductor elements. There are various, often conflicting theories, trying to explain the nature of 1/f-noise and, in particu- lar, to determine its relationship with Random Telegraph Signal (RTS). Observed noise, which has the character of RTS, is seen against the background of other noises in many electronic devices [5]. Some researchers suggest that the 1/f-noise is a superposition of several random RTS processes with different characteristic frequencies. Others suggest that 1/f-noise arises due to fluctuations in carrier mobility, and RTS is associated with carrier trapping, leading to a change in charge carrier concentration and, conse- quently, to conductivity fluctuations. Recently, RTS has been described as an impulse noise exhibiting a stepwise change in signal level. This type of the noise manifests itself as a two-level RTS with the same height of current pulses and with randomly distributed time intervals between pulses [6]. In addition, the formation of the multi-level RTS with several discrete levels is possible. Low-frequency 1/f-noise is tradi- tionally used as an indicator of quality and reliability for semiconductor devices. Therefore, these studies are of interest for transistors based on ZnO [7]. The aim of this work is an experimental study of the low-frequency noise of field-effect transistors based on ZnO:Li films. 2. EXPERIMENT To conduct studies of noise characteristics, transistors were manufactured by two different methods [8, 9]. In the first case, a doping impurity, acceptor or donor, was introduced into the film uniformly in thickness