Controlled Growth of ZnO films on Si Substrate and N-doping Behavior
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Controlled Growth of ZnO films on Si Substrate and N-doping Behavior Y. F. Mei1, Ricky K. Y. Fu1, R. S. Wang2, K. W. Wong1, H. C. Ong2, L. Ding3, W. K. Ge3, G. G. Siu1, and Paul K. Chu1,* 1 Department of Physics and Materials Science, City University of Hong Kong, Hong Kong 2 Department of Physics, Chinese University of Hong Kong, Shatin, Hong Kong 3 Department of Physics, Hong Kong University of Science & Technology, Hong Kong ABSTRACT ZnO films with orientations of (001), (110), and (100) were fabricated on silicon by different substrate biases at low temperature. Dynamic cathodoluminescence (CL) dependence on electron bombardment revealed unstable Zn-N bonding if N2 was used as a predecessor. CL under various accelerated voltages showed the possible energies of Zn-N. N-related photoluminescence (PL) at low temperature confirmed that nitrogen was released after annealing. These N-doping behaviors agreed to the theoretical calculation. INTRODUCTION Recently, the fabrication of ZnO films by the filtered cathodic vacuum arc (FCVA) technique has aroused interests because of the readily adjustable deposition parameters, large area, low growth temperature, and convenient in-situ doping when conducted under an overlying plasma [1-6]. ZnO films have been synthesized under non-equilibrium conditions in our plasma immersion ion implantation and deposition (PIII&D) system that is similar to FCVA because of the high kinetic energies of the precursors accelerated by the substrate bias and low substrate temperature [7]. Hence, films with unique properties can be fabricated on silicon, and more information can be obtained to fathom the growth mechanism of ZnO films. In this work, (001), (110), and (100) ZnO films were synthesized on silicon by using different substrate biases at low temperature. The N-doping behavior was investigated using dynamic cathodoluminescence (CL) under various accelerated voltages to determine the possible energies of Zn-N. Comparison of the photoluminescence (PL) spectra acquired from ZnO single crystal, undoped ZnO film, fresh N-doped ZnO film, and N-doped ZnO films after rapid thermal annealing (RTA) showed the N-related PL ranges and demonstrated unstable Zn-N bonding. EXPERIMENTAL DETAILS The substrates were 10 ~ 30 Ω⋅cm p-type (100) silicon wafers. The base pressure in the vacuum chamber of our plasma immersion ion implanter equipped with a cathodic arc vacuum arc source was about 1 × 10-5 Torr [7, 8]. The zinc plasma was formed in the cathodic arc source, guided through a magnetic filter to reduce detrimental macro-particles, and drifted into the vacuum chamber. Oxygen gas (flow rate: 20 sccm; pressure: ~ 1.0 × 10-3 Torr) was simultaneously bled into the vacuum chamber during deposition and interacted with the drifting zinc plasma thereby producing a dual plasma consisting of both zinc and oxygen ions. The samples that were biased from 0 to -300 V were positioned about 10 cm from the exit of the plasma stream. To produce N-doped films, a mixture of gases [flow rate (O2: N2, sccm): 5: 15
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