ZnO films deposited by optimized PLD technique with bias voltages

Abstract

The pulsed laser deposition (PLD) technique with bias voltage application for formation of high quality ZnO films was investigated. Oxygen ambient in the PLD chamber significantly decreased the photoluminescence (PL) intensity of near band edge (NBE) emission. Then, instead of using oxygen ambient, the PLD technique with bias voltage application was optimized to attain the stoichiometric composition of the ZnO films. As the deposition temperature was increased, the X‐ray spectrum width diffracted from the (0002) planes was decreased and it showed a minimum value at 700 °C. The PL intensity of the NBE emission also had its maximum value for the film deposited at 700 °C. For the ZnO films deposited at 700 °C, the X‐ray spectrum width showed the minimum value under a bias voltage of –50 V. The PL intensity of the NBE emission also had a maximum value under the same bias voltage. Thus, ZnO films deposited under a bias voltage of –50 V at 700 °C had strong NBE emission intensities. These results could be explained not only by attaining the stoichiometric composition of the ZnO film but also by decreasing the number of high energy O2– ions which caused non‐radiative recombination centers in the film. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Defect‐related mechanism of ferromagnetic behaviors for ZnCoO:H films formed by PLD with bias voltage application

“…In this paper, we observed the saturation magnetization (M s ) of the ZnCoO:H films formed by changing the defect concentration using two techniques (the oxygen partial pressure and the PLD bias voltage [14]) and found that as the defect concentration was increased, M s significantly decreased but sometimes increased. We also found that the defect concentration certainly affected the saturation magnetization but it did so only through the shift of the Fermi level.…”

“…If positive (negative) ions were accelerated by a negative (positive) bias voltage on the grid, they would be decelerated by a positive (negative) bias voltage between the grid and the substrate. Accordingly, this bias voltage technique simply controlled the ratio of the positive and the negative ions without increasing their kinetic energy [14]. A Nd:YAG laser (266 nm) was utilized for the ablation; the pulse duration was 10 ns, the repetition rate was 10 Hz and the output energy was 75 mJ.…”

“…A typical deposition rate of the films was about 3nm/min. Sapphire (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) substrates were thermally cleaned at 800 °C for 30 min in the chamber and a ZnO buffer layer was deposited at 400 °C for 30 min. After 800 °C annealing of the buffer layer for 10 min in the PLD chamber, ZnCoO films were deposited at 700 °C.…”

Characteristics of ZnO/CuO heterojunctions formed by direct bonding and PLD with bias voltage application

“…To date, several techniques have been proposed to overcome these problems. Some examples include: using the pulsed laser deposition (PLD) technique to precisely control partial pressures of the oxygen ambient in the deposition chamber in order to attain the stoichiometric composition of ZnO films [3,4]; and applying bias voltages on the mesh grid in the deposition chamber in order to control the ratio of Zn and O ions which arrive at the substrates [5][6][7]. Various heterojunction structures have also been pro-posed to form n-type ZnO/p-type other semiconductors to avoid using p-type ZnO [8][9][10][11][12].…”

“…An n-ZnO film was deposited on the n-ZnO substrate by the PLD technique with bias voltage application. The details of the bias voltage PLD system are described elsewhere [7]. If a positive bias voltage is applied on the grid electrode, positive ions (Zn 2+ ) are repelled and negative ions (O 2-) are attracted, while if a negative bias voltage is applied on the electrode, negative ions are repelled, and positive ions are attracted.…”