Chin-Ching Lin

Properties of nitrogen-implanted p-type ZnO films grown on Si3N4/Si by radio-frequency magnetron sputtering

An nitrogen-implanted p-type ZnO film has been grown on a Si substrate buffered with Si3N4 using radio-frequency magnetron sputtering. The Si3N4 buffer layer can effectively improve film stoichiometry and reduce the formation of oxygen vacancies compared to ZnO on Si. The electrical properties of the p-type ZnO films implanted with 5×1012–1×1014 cm−2 N+ dose show a hole concentration of 5.0×1016–7.3×1017 cm−3, hole mobility of 2.51–6.02 cm2/V s, and resistivity of 10.11–15.3 Ω cm. The p-type ZnO films also showed an excellent crystallinity and a strong ultraviolet emission peak near 3.30 eV at room temperature. Moreover, as evidenced by extended x-ray absorption fine structure analysis, the local structure of the p-type ZnO films was changed due to the substitution of nitrogen ions for oxygen ions in p-type ZnO films. Our finding of p-type ZnO films grown on a Si3N4/Si substrate could provide a simple method to fabricate reproducible p-type ZnO films on silicon substrate for the development of large-scale...

Enhanced luminescent and electrical properties of hydrogen-plasma ZnO nanorods grown on wafer-scale flexible substrates

Photoelectronic characteristics are performed in well-aligned hydrogen-plasma ZnO nanorods grown on 4 in. flexible organic substrates buffered with ZnO film. Enhancement of photoluminescence (PL) properties due to H2 plasma treatment by a factor of 60 times for relative intensity ratio (ultraviolet emission to deep level emission) has been observed. X-ray photoelectron spectroscopy analysis reveals that the enhanced PL property is attributed to both defect passivation and modification on the surface region of ZnO nanorods due to the absorption of hydrogen ions. However, the PL spectra of H2 plasma ZnO nanorods can be restored to the original state of ZnO nanorods by thermal annealing process. The current-voltage measurements suggest that the n-type ZnO nanorods with H2 plasma treatment present a higher conductivity of about 5–6 orders of magnitude than the nonplasma ZnO nanorods.

Core-shell CuInS2/ZnS quantum dots assembled on short ZnO nanowires with enhanced photo-conversion efficiency

A novel quantum-dot-based solar cell assembly consisting of core-shell Zn-doped CuInS2@ZnS (Zn-CIS@ZnS) quantum dots associated with short ZnO (5 μm in length) nanowires was developed and systematically investigated in terms of its nanostructure and optical properties, associated with corresponding solar cell parameters, i.e., VOC, JSC, fill factor (FF). In this investigation, the photo-conversion efficiency of the Zn-CIS-based solar cells without the presence of the ZnS shell can be readily tuned by controlling the Zn/Cu ratio. Furthermore, the efficiency was significantly improved upon the deposition of a thin ZnS shell on these Zn-CIS QDs, where a significant enhancement in short-circuit current density (JSC) by 88% was observed because the ZnS coating is able to effectively eliminate excited electron recombination and enhance the charge transfer efficiency from Zn-CIS QDs to ZnO nanowires. Power-conversion efficiency as high as 0.71% can be attained, which is improved more than 2–3 times compared with that without ZnS coating. Such a unique nanoarchitecture through coupling with both core-shell QDs and short ZnO nanowires suggests a promising design for a quantum dot-based solar cell with considerably improved power-conversion efficiency.

Magnetophotoluminescence properties of Co-doped ZnO nanorods

We present the detailed experimental results of the magnetic and optical properties of cobalt doped ZnO nanorods, especially the temperature and magnetic field dependence of photoluminescence up to 14 T. The Raman measurements indicate that our Co-doped ZnO nanorods have the same lattice constant as crystalline bulk ZnO. Sharp luminescence peaks centered at around 670 nm were observed at low temperature and their intensity decreased with increasing magnetic field. The luminescence peaks were attributed to d-d transitions in the Ligand field from the doped Co ions. We also observed a diamagnetic shift at a temperature of 1.5 K when the magnetic field was scanned from 0 to 14 T. The exciton radius of the Co-doped ZnO nanorods was deduced from the magnetophotoluminescence results.

Synthesis and optical properties of ZnO–ZnS core-shell nanotube arrays

Heterostructured ZnO–ZnS core-shell nanotube arrays with the diameters of 50–80nm and lengths up to 1μm were synthesized by a two-step chemical reaction. First, the ZnO layer was grown by atomic-layer deposition. It was found that the preferred growth orientation was strongly dependent on the substrate temperature. After sulfuration conversion from arrayed ZnO nanorods, the ZnS–ZnO composite arrays can be successfully prepared, as evidenced from transmission electron microscopy. This confirms that the ZnO–ZnS core-shell nanotube-arrayed structure has been fabricated. X-ray photoelectron spectroscopy analysis indicates that the binding energy of S 2p is the same as that of bulk single-crystal ZnS and that the Zn 2p3∕2 peak is shifted about 0.5eV due to the formation of Zn–S bonds. Photoluminescence shows the relative-intensity ratio of ultraviolet emission (IUV) to deep-level emission (IDLE) for ZnO∕ZnS core-shell nanotubes can be enhanced to be nine times that of original ZnO nanotubes.

Fully silicided NiSi gate on La 2 O 3 MOSFETs

We have fabricated the fully silicided NiSi on La/sub 2/O/sub 3/ for n- and p-MOSFETs. For 900/spl deg/C fully silicided CoSi/sub 2/ on La/sub 2/O/sub 3/ gate dielectric with 1.5 nm EOT, the gate dielectric has large leakage current by possible excess Co diffusion at high silicidation temperature. In sharp contrast, very low gate leakage current density of 2/spl times/10/sup -4/ A/cm/sup 2/ at 1 V is measured for 400/spl deg/C formed fully silicided NiSi and comparable with Al gate. The extracted work function of NiSi was 4.42 eV, and the corresponding threshold voltages are 0.12 and -0.70 V for respective n- and p-MOSFETs. Electron and hole mobilities of 156 and 44 cm/sup 2//V-s are obtained for respective n- and p-MOSFETs, which are comparable with the HfO/sub 2/ MOSFETs without using H/sub 2/ annealing.

Formation of Ni germano-silicide on single crystalline Si/sub 0.3/Ge/sub 0.7//Si

We have studied the Ni and Co germano-silicide on Si/sub 0.3/Ge/sub 0.7//Si. The Ni germano-silicide shows a low sheet resistance of 4-6 /spl Omega///spl square/on both P/sup +/N and N/sup +/P junctions, which is much smaller than Co germano-silicide. In addition, small junction leakage currents of 3/spl times/10/sup -8/ A/cm/sup 2/ and 2/spl times/10/sup -7/ A/cm/sup 2/ are obtained for Ni germano-silicide on P/sup +/N and N/sup +/P junctions, respectively. The good germano-silicide integrity is due to the relatively uniform thickness as observed by cross-sectional TEM.

Electron transport behavior of individual zinc oxide coated single-walled carbon nanotubes.

Uniform zinc oxide coated single-walled nanotubes (SWNTs) were fabricated by ultrasonic irradiation with acid-treated SWNTs, zinc acetate, and triethanolamine at low temperature in aqueous phase processing. The ZnO coating process did not decrease the dark current of the SWNTs, but a real decrease in the steady state negative photocurrent was observed after ZnO coating, suggesting a clear photosensitization effect. Transport measurements reveal that the negative photocurrent in s (semiconducting)-SWNTs@ZnO could be described by electron-hole compensation behavior attributed to the ZnO layer under ultraviolet excitation. This simple coating method for one-dimensional material can open up new possibilities for multifunctional nanodevices.

Enhanced UV photoresponse in nitrogen plasma ZnO nanotubes.

The photoresponse behavior of one-dimensional ZnO nanowires (NWs) and nanotubes (NTs) grown on ITO-coated glass substrates via a wet-chemical route was investigated. The photoluminescence spectra exhibited a decrease in the deep-level intensity, indicating that the oxygen defects and impurities are occupied by the presence of N ions in the ZnO NT matrix after a nitrogen plasma treatment. I-V tests demonstrate an enhanced dark current (4.83 x 10(-7) A) after an extended plasma treatment of up to 900 s for ZnO NTs compared to that (0.571 x 10(-7) A) of NWs. Furthermore, the ZnO NTs show the highest reliable photoresponse, 20 times that of NWs under UV irradiation (325 nm) in air at room temperature. It is believed that nitrogen plasma ZnO nanotubes can potentially be useful in the designs of 1D ZnO-based solar cells and optoelectronic devices.

Ultraviolet Emission in ZnO Films Controlled by Point Defects

The undoped ZnO films were grown on silicon (001) substrates by radio frequency magnetron sputtering. The dependence of defect formation and photoluminescence (PL) of ZnO films on the annealing temperature and oxygen mole ratio (OMR) were investigated using X-ray diffraction and PL spectra. A sharp ZnO (002) peak with a strong UV emission peak around 3.28 eV can be obtained for the films annealed in O 2 and N 2 atmospheres. However, the films annealed in nitrogen show strong deep-level emission peaks that vary with the annealing temperature. Below 850°C, Zn interstitials become the dominant point defects, but for the ZnO films annealed at higher temperatures such as 1000°C, oxygen vacancies become the predominant point defects. In contrast, in an oxygen atmosphere, a strong UV emission along with invisible deep-level peaks can be detected for ZnO films sputtered at an OMR of 5% and annealed at 850°C. This result is attributed to the enhanced crystallization and a reduced defect concentration.