Effect of disorder on carrier transport in ZnO thin films grown by atomic layer deposition at different temperatures

Abstract

We have grown $200 nm thick ZnO films on (0001) sapphire substrates using atomic layer deposition at different substrate temperatures ranging from $150 to 350 C. X-ray diffraction and photoluminescence spectra of these films showed that crystalline and compositional native defects were strongly dependent on the substrate temperature. Room temperature Hall measurement showed that all the films were degenerate with carrier concentration exceeding the Mott's critical density n c required for metallic conduction. The lowest value of room temperature resistivity $3.6 Â 10 À3 X cm was achieved for the film deposited at $200 C, which had an estimated carrier concentration $5.7 Â 10 19 cm À3 and mobility $30 cm 2 /V s. The films deposited both below and above $200 C showed increased resistivity and decreased mobility presumably due to the intensified defects and deteriorated crystalline quality of these films. To investigate the effect of disorder on the underlying charge transport mechanisms in these films, the electrical resistivity was measured in the temperature range of $4.2 to 300 K. The films grown at $150, 300, and 350 C were found to be semiconducting in the entire range of the measurement temperature due to the intensified disorder which impeded the metallic transport in these films. However, the films grown at $200 and 250 C showed a transition from metallic to semiconducting transport behaviour at lower temperatures due to the reduced defects and improved crystalline quality of these films. The observed semiconducting behaviour below the transition temperature for these films could be well explained by considering quantum corrections to the Boltzmann conductivity which includes the effect of disorder induced weak localization and coulomb electron-electron interactions. V C 2013 AIP Publishing LLC. [http://dx.

Weak localization and size effects in thin In 2 O 3 films prepared by autowave oxidation

“…Negative MR in TCO is often observed in the weak localization regime. Furthermore, such cases are usually observed at low temperatures [15,24]. An understanding of the experimental data based on the WL model requires the existence of extended states at low temperatures.…”

“…Disorder in semiconductors can be created by film growth [23][24][25] or doping [26]. In disordered semiconductors, where there is a large amount of impurities or defects, electrons in diffuse mode can have multiple scatterings from impurities or defects without a loss of energy that is the elastic collision.…”

Effect of growth temperature on diode parameters of n-ZnO/p-Si heterojuction diodes grown by atomic layer deposition

“…This additional oxygen in the form of OH groups can act as acceptors thereby reducing the electron concentrations [13,14]. On the contrary when growth temperature was increased beyond 200°C, oxygen vacancy and Zn interstitial related defects may be created due to decomposition of precursors on heated substrate surface [13,15]. These defects are donor type defects which can increase the electron concentration in the ensuing ZnO films [1,15].…”

“…On the contrary when growth temperature was increased beyond 200°C, oxygen vacancy and Zn interstitial related defects may be created due to decomposition of precursors on heated substrate surface [13,15]. These defects are donor type defects which can increase the electron concentration in the ensuing ZnO films [1,15]. Moreover some first principle theoretical studies have revealed that Hydrogen may be a potential donor in ZnO [25], but according to experimental studies of Guziewicz et al Hydrogen does not act as a dominant donor in ZnO thin films grown by ALD [26].…”

“…The n-ZnO/p-Si heterojunctions have been grown by various growth techniques like pulse laser deposition [1], RF sputtering [3], metal organic chemical vapor deposition [6], solution growth [12] etc. Recently atomic layer deposition (ALD) has emerged as a promising growth methodology for growing metal oxides' thin films for practical device applications due to its fine control over film thickness, good thickness uniformity in large substrate area, comparatively low-temperature deposition process and high-degree of repeatability in film properties [13][14][15].…”