Homo- and heteroepitaxial ZnMgO:Al, ZnCaO:Al and ZnO:Ga films have been grown on sapphire and ZnO substrates by RF (13.56 MHz) reactive magnetron sputtering from oxidic targets. The films grow epitaxially, i.e. with a preferred in-plane and out-of plane orientation. However, the heteroepitaxial films on sapphire exhibit a much higher crystallographic defect density, compared to the homepitaxial films. The ZnMeO films (Me – metal)on a-plane sapphire exhibit a lower defect density leading to higher Hall mobilities. Both, homo- and heteroepitaxial ZnO:Ga films with carrier concentrations N>1020 cm−3 exhibit the same mobility values, which increase with increasing carrier concentration. This behaviour is typical for electrical grain barrier limited transport, as decribed recently for polycrystalline ZnO:Al(Ga) films on glass. For the ZnCaO:Al films, deposited at similar conditions as the ZnO:Ga films, much lower carrier concentrations were measured, both for sapphire as well as for ZnO substrates. The mobilities of the ZnCaO:Al films on ZnO are much higher than that on the sapphire single crystals. The measured Hall mobilities are compared to single crystalline ZnO transport data.

Additionally, the work functions of the ZnMeO layers have been measured by X-ray and ultra-violet photoelectron spectroscopy. As expected, the work functions are lower compared to unalloyed ZnO, which can be used for ZnO band gap and band alignment engineering.

In this paper effects of NH3 doping on ZnO thin films grown by metal organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates using diethyl zinc (DEZn) and O2 precursors and N2 as the carrier gas have been studied. NH3 flow rates were varied from 0.1% to 4% in the growth runs. All the runs were done at 500°C at 10 Torr pressure.

The XRD measurements show a single ZnO (002) peak. Raman data for the samples confirms presence of ZnO:N modes at 275cm−1, 510cm−1 and 575 cm−1 and 645cm−1. The PL results for Zn rich films show weak broad peaks centered at 480nm and 650nm with no ZnO band edge emission, while oxygen rich films show weak ZnO band edge emission and a strong broad orange peak centered at 650nm. Hall effect measurements indicate that all of the as-grown films are highly resistive. Some are weakly p-type with carrier concentration of 4.24 × 1014 cm−3 and mobility of 16.55 cm2/Vs. Annealing in N2 ambient for 60 minutes at 800°C enhances the PL band edge emission and converts all the films to highly conducting n-type, with carrier concentration on the order of 8 × 1018 cm−3, mobility on the order of 12 cm2/Vs and resistivity of 0.063 Ω-cm.

This work emphasizes room temperature deposition and fabrication of staggered bottom-gate ZnO and IZO TFTs. We synthesized these oxide thin films by RF sputtering in an Ar/Oxygen ambience with no intentional heating of the substrates. Bottom gate staggered structure ZnO TFTs were fabricated (Ti/Au/Ti gate and Au/Ti source/drain) and characterized. ZnO TFTs retained well-behaved transfer characteristics down to a channel length of 4 μm with field effect mobility of 5 cm2/V.s, on/off current ratio exceeding 106 and threshold voltage around -5V. The IZO TFTs, with ITO as gate metal layer and highly conducting amorphous IZO forming the source/drain material had reasonably high field effect mobility of 20 cm2/V.s and on/off current ratio exceeding 106, which are well suited for active matrix display applications. Finally, to demonstrate the viability of oxide-based device integration, simple circuits such as inverters and pseudo-logic circuits are designed, fabricated and tested.

Nb-doped anatase TiO2 films were deposited on unheated glass by dc magnetron sputtering using a slightly reduced TiO2-x–Nb2O5-x target with oxygen flow ratios [O2/(Ar+O2)] in the range from 0.00 to 0.20%. After post-annealing in a vacuum (6 × 10−4 Pa) at 500 and 600 °C for 1 h, the films were crystallized into the polycrystalline anatase TiO2 structure. The resistivity of the both films decreased to 6.3-6.8 × 10−4 Ω·cm with increasing [O2/(Ar+O2)] to 0.10%, where the carrier density and Hall mobility were 1.9-2.0 × 1021 cm−3 and 4.9-5.0 cm2·V−1·s−1, respectively. The films exhibited high transparency of over 60-70% in the visible region of light.