Trap states and space charge limited current in dispersion processed zinc oxide thin films

Abstract

The electric transport properties of nanoparticulate zinc oxide (ZnO) thin films are investigated in nitrogen and ambient atmosphere with respect to the effects of polymer adsorbates, in order to study the origin of hysteresis behavior of ZnO thin film transistors. A strong dependence on the polymer adsorbate of the conductivity in nitrogen atmosphere is observed. Utilizing the space charge limited current theory, the trap depth and concentration in the films have been estimated. According to this analysis, the low conductivity of polymer free thin films in ambient atmosphere is caused by an increase in deep traps, compensating free charge carriers and not by a reduction in donorlike defect states. Furthermore, polymeric additives seem to induce similar trap states, which make the transport properties less sensitive against atmospheric influences. However, the strongly compensated semiconductor created in this way, causes a slow trap and release behavior resulting in a strong hysteresis in the transistor characteristics and long-term instabilities. It is shown, that ignoring these time-dependent characteristics, straight forward derived transistor parameters like the field effect mobility can be easily overestimated.

Hysteresis-free DC conduction in zinc oxide films with a conducting polymer counter electrode

“…The maximum µ obtained, from the intercept of linear plot between log I versus 2log V at room temperature, is 0.0426 cm 2 /Vs. Similar SCLC has been reported for 330 nm thick ZnO film with 10% polymethyl vinyl etheralt-maleic anhydride stabilisers on glass substrates at room temperature under atmospheric condition [38]. The inset of Fig.…”

Enhancement and tuning of the defect-induced electroluminescence of ZnO mesoporous layers in the visible range

“…The I-V curve cannot be fitted with the usual exponential function typical of a P-N junction, but rather with a succession of power laws with different exponents. This observation is indicative of a space-chargelimited current (SCLC), a regime already observed in several transport studies on ZnO [27][28][29][30][31]. In some instances, the value of the exponents used to fit the different parts of the curve, as well as the voltage ranges at which each power law occurs can be used to extract quantitative information on the nature and the density of the defect states [32].…”

Improved sensitivity of polychlorinated-biphenyl-orientated porous-ZnO surface photovoltage sensors from chemisorption-formed ZnO-CuPc composites

“…As ordinary ZnO is an n -type semiconductor due to its intrinsic-defect-induced stoichiometry deviation 23 , a stable and visible-light-sensitive p -type semiconductor may be a suitable modification material to enhance the electron transfer from the p -type medication material to the n -type semiconductor ZnO under illumination. Since the surface states usually act as the charge traps 24 , so some transferring electrons may be captured in the ZnO's surface states. As a result, the electron population in the ZnO's surface states can be increased significantly, leading to enormously enhanced SPV-signal.…”