ZnO thin-films are grown on a p-Si(111) substrate by RF sputtering. The effects of growth temperature and O2 mixture ratio on the ZnO films are investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and roomtemperature photoluminescence (PL) measurements. All the grown ZnO thin films show a strong preferred orientation along the c-axis, with an intense ultraviolet emission centered at 377 nm. However, when O2 is mixed with the sputtering gas, the half width at half maximum (FWHM) of the XRD peak increases and the deep-level defect-related emission PL band becomes pronounced. In addition, an n-ZnO/p-Si heterojunction diode is fabricated by photolithographic processes and characterized using its current-voltage (I-V) characteristic curve and photoresponsivity. The fabricated n-ZnO/p-Si heterojunction diode exhibits typical rectifying I-V characteristics, with turn-on voltage of about 1.1 V and ideality factor of 1.7. The ratio of current density at ± 3 V of the reverse and forward bias voltage is about 5.8 × 103, which demonstrates the switching performance of the fabricated diode. The photoresponse of the diode under illumination of chopped with 40 Hz white light source shows fast response time and recovery time of 0.5 msec and 0.4 msec, respectively.

Nanostructures of ZnO, such as nanowires, nanorods, nanorings, and nanobelts have been actively studied andapplied in electronic or optical devices owing to the increased surface to volume ratio and quantum confinement that theyprovide. ZnO seed layer (about 40nm thick) was deposited on Si(100) substrate by RF magnetron sputtering with power of60 W for 5 min. ZnO nanorods were grown on ZnO seed layer/Si(100) substrate at 95oC for 5 hr by hydrothermal methodwith concentrations of Zn(NO3)2·6H2O [ZNH] and (CH2)6N4 [HMT] precursors ranging from 0.02M to 0.1M. We observed themicrostructure, crystal structure, and photoluminescence of the nanorods. The ZnO nanorods grew with hexahedron shape tothe c-axis at (002), and increased their diameter and length with the increase of precursor concentration. In 0.06 M and 0.08M precursors, the mean aspect ratio values of ZnO nanorods were 6.8 and 6.5; also, ZnO nanorods had good crystal quality.Near band edge emission (NBE) and a deep level emission (DLE) were observed in all ZnO nanorod samples. The highestpeak of NBE and the lower DLE appeared in 0.06 M precursor; however, the highest peak of DLE and the lower peak ofNBE appeared in the 0.02 M precursor. It is possible to explain these phenomena as results of the better crystal quality andhomogeneous shape of the nanorods in the precursor solution of 0.06 M, and as resulting from the bed crystal quality and theformation of Zn vacancies in the nanorods due to the lack of Zn++ in the 0.02 M precursor.

In this study, the effects of an annealed buffer layer with different thickness on heterojunction diodes based on the ZnO/ZnO/p-Si(111) systems were reported. The effects of an annealed buffer layer with different thickness on the structural, optical, and electrical properties of zinc oxide (ZnO) films on p-Si(111) were also studied. Before zinc oxide (ZnO) deposition, different thicknesses of ZnO buffer layer, 10 nm, 30 nm, 50 nm and 70 nm, were grown on p-Si(111) substrates using a radio-frequency sputtering system; samples were subsequently annealed at 700˚C for 10 minutes in N2 in a horizontal thermal furnace. Zinc oxide (ZnO) films with a width of 280nm were also deposited using a radio-frequency sputtering system on the annealed ZnO/p-Si (111) substrates at room temperature; samples were subsequently annealed at 700˚C for 30 minutes in N2. In this experiment, the structural and optical properties of ZnO thin films were studied by XRD (X-ray diffraction), and room temperature PL (photoluminescence) measurements, respectively. Current-voltage (I-V) characteristics were measured with a semiconductor parameter analyzer. The thermal tensile stress was found to decrease with increasing buffer layer thickness. Among the ZnO/ZnO/p-Si(111) diodes fabricated in this study, the sample that was formed with the condition of a 50 nm thick ZnO buffer layer showed a strong c-axis preferred orientation and I-V characteristics suitable for a heterojunction diode.

We studied the initial reaction mechanism of Zn precursors, namely, di-methylzinc (Zn(CH3)2, DMZ) and diethylzinc (Zn(C2H5)2, DEZ), for zinc oxide thin-film growth on a Si (001) surface using density functional theory. We calculated the migration and reaction energy barriers for DMZ and DEZ on a fully hydroxylized Si (001) surface. The Zn atom of DMZ or DEZ was adsorbed on an O atom of a hydroxyl (-OH) due to the lone pair electrons of the O atom on the Si (001) surface. The adsorbed DMZ or DEZ migrated to all available surface sites, and rotated on the O atom with low energy barriers in the range of 0.00-0.13 eV. We considered the DMZ or DEZ reaction at all available surface sites. The rotated and migrated DMZs reacted with the nearest -OH to produce a uni-methylzinc (-ZnCH3, UMZ) group and methane (CH4) with energy barriers in the range of 0.53-0.78 eV. In the case of the DEZs, smaller energy barriers in the range of 0.21-0.35 eV were needed for its reaction to produce a uni-ethylzinc (-ZnC2H5, UEZ) group and ethane (C2H6). Therefore, DEZ is preferred to DMZ due to its lower energy barrier for the surface reaction.