Development of ZnO-based thin film transistors and phosphorus-doped ZnO and (Zn, Mg)O by pulsed laser deposition.

摘要

Top-gate type ZnO-based TFTs were fabricated on glass substrate via photolithography and wet chemical etching processing. The ZnO layers were deposited using pulsed laser deposition (PLD). N-channel depletion-mode operation was shown for the undoped ZnO and P-doped ZnO thin film transistors. The current-voltage measurements demonstrated an enhancement-mode device operation for the thin film transistors with P-doped (Zn,Mg)O as the active channel layer.; P-type phosphorus-doped (Zn0.9Mg0.1)O films have been realized via PLD without post-annealing process. The conduction type of the films strongly depends on the oxygen partial pressure during the deposition process. Increasing the oxygen partial pressure from 20 to 200 mTorr yielded a carrier type conversion from n-type to p-type. The P-doped (Zn,Mg)O films grown at 150 mTorr oxygen partial pressure were p-type and exhibited a hole concentration of 2.7 x 1016 cm-3, a mobility of 8.2 cm2/Vs and a resistivity of 35 O-cm.; (Zn0.9Mg0.1)O:P/ZnO heterostructures were fabricated on sapphire and ZnO substrates via PLD with Au and Ti/Au served as Ohmic contacts. Both structures exhibit rectifying electrical characteristics. The turn-on voltages were determined to be 1.36 V and 1.15 V for the structure grown on sapphire and ZnO substrate, respectively.; The resistivity of Al-doped ZnO depends on growth temperature, laser energy and oxygen pressure. The photoluminescence properties of the Al-doped ZnO films have strong correlations to the electrical properties and crystallinity of the films. The possibility of the non-radiative trapping through deep level defect states decreases with increasing the electron density of Al-doped ZnO films. AFM results showed that the root-mean-square roughness increases with growth temperature and oxygen partial pressure.; The resistivity of the as-deposited 0.2 at.% P-doped films grown in ozone/oxygen ambient rapidly increased with growth temperature. The improvement in band edge emission intensity for the films grown in O2/Ar/H2 mixture may reflect the passivation effect of the deep acceptor-related levels by hydrogen, which also yields the passivation of the deep level emission. Oxygen interstitials may contribute to the deep level emission of RT-PL for annealed P-doped ZnO films.