Tse-Pu Chen

Simple Fabrication Process for 2D ZnO Nanowalls and Their Potential Application as a Methane Sensor

Two-dimensional (2D) ZnO nanowalls were prepared on a glass substrate by a low-temperature thermal evaporation method, in which the fabrication process did not use a metal catalyst or the pre-deposition of a ZnO seed layer on the substrate. The nanowalls were characterized for their surface morphology, and the structural and optical properties were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence (PL). The fabricated ZnO nanowalls have many advantages, such as low growth temperature and good crystal quality, while being fast, low cost, and easy to fabricate. Methane sensor measurements of the ZnO nanowalls show a high sensitivity to methane gas, and rapid response and recovery times. These unique characteristics are attributed to the high surface-to-volume ratio of the ZnO nanowalls. Thus, the ZnO nanowall methane sensor is a potential gas sensor candidate owing to its good performance.

Bending effects of ZnO nanorod metal–semiconductor–metal photodetectors on flexible polyimide substrate

The authors report the fabrication and I-V characteristics of ZnO nanorod metal–semiconductor–metal photodetectors on flexible polyimide substrate. From field-emission scanning electron microscopy and X-ray diffraction spectrum, ZnO nanorods had a (0002) crystal orientation and a wurtzite hexagonal structure. During the I-V and response measurement, the flexible substrates were measured with (i.e., the radius of curvatures was 0.2 cm) and without bending. From I-V results, the dark current decreased, and the UV-to-visible rejection ratio increased slightly in bending situation. The decreasing tendency of the dark current under bending condition may be attributed to the increase of the Schottky barrier height.

Low-Frequency Noise Characteristics of ZnO Nanorods Schottky Barrier Photodetectors

A Schottky barrier photodetector with ZnO nanorods is fabricated on a glass substrate and the I-V characteristics are investigated. The ZnO nanorods are synthesized by an aqueous method, which allowed the fabricated Schottky barrier photodetector to be more sensitive in the UV region. Under 370-nm illumination, the photocurrent of the ZnO nanorod Schottky barrier photodetector is 6.56 μA and the UV-to-visible ratio is 780.8 at -1V. In addition, the noise equivalent power and normalized detectivity (D*) of the photodetector are 6.74×10-13 W and 3.29 ×1011 cmHz0.5W-1 at -1V, respectively.

Synchrotron radiation based cross-sectional scanning photoelectron microscopy and spectroscopy of n-ZnO:Al/p-GaN:Mg heterojunction

Al-doped ZnO (AZO) deposited by radio frequency co-sputtering is formed on epitaxial Mg-doped GaN template at room temperature to achieve n-AZO/p-GaN heterojunction. Alignment of AZO and GaN bands is investigated using synchrotron radiation based cross-sectional scanning photoelectron microscopy and spectroscopy on the nonpolar side-facet of a vertically c-axis aligned heterostructure. It shows type-II band configuration with valence band offset of 1.63 ± 0.1 eV and conduction band offset of 1.61 ± 0.1 eV, respectively. Rectification behavior is clearly observed, with a ratio of forward-to-reverse current up to six orders of magnitude when the bias is applied across the p-n junction.

Optoelectronic Properties of Thermally Evaporated ZnO Films with Nanowalls on Glass Substrates

Zinc oxide (ZnO) films with two-dimensional (2D) vertically aligned nanowalls, denoted by nanowalls-films, are successfully prepared on glass substrates at a low growth temperature of 450 °C without using metal catalysts. The morphology and optical properties of the nanowalls-film are characterized by scanning electron microscopy, X-ray diffraction analysis, transmission electron microscopy, energy dispersive X-ray spectroscopy, and photoluminescence measurement. The ZnO nanowalls-film show a strong UV emission and a preferred c-axis orientation with a hexagonal structure. The UV sensor measurement of the ZnO nanowalls-film shows a high sensitivity to UV light, rapid rise and decay times, and a good UV-to-visible rejection ratio.

Effect of surface modification by self-assembled monolayer on the ZnO film ultraviolet sensor

A simple surface modification process to reduce the negative influences of oxygen vacancies/surface contamination and promote the performance of ZnO ultraviolet (UV) sensor is reported. ZnO film was self-assembled by 3-aminopropyltrimethoxysilane (APTMS) molecules for passivating its surface defects. APTMS molecules are hydrolyzed at the methoxy end, and then condensed with the substrate hydroxyl groups to produce siloxanes. Compared with the conventional ZnO UV sensor, in which the reproducibility and homogeneity of device performance strongly suffer from a difficulty in controlling the ZnO surface state conditions, the APTMS molecules leads to a reduction of the dark leakage current by more than 2 orders of magnitude.

Growth and Characterization of ZnSe/CdSe Multiquantum Disks

The authors report the growth of high-density ZnSe/CdSe multiquantum disks on oxidized Si substrate. It was found the as-grown nanotips were tapered with the mixture of cubic zinc blende and hexagonal wurtzite structures. Also, photoluminescence intensities observed from these ZnSe/CdSe multiquantum disks were much larger than that observed from the homogeneous ZnSe. Activation energies for the ZnSe/CdSe multiquantum disks with well widths Lw of 8, 12, and 16 nm were 22, 62, and 56 meV, respectively.

Low-Frequency Noise Characteristics of GaN Schottky Barrier Photodetectors Prepared With Nickel Annealing

In this paper, GaN Schottky barrier photodetectors (PDs) prepared with and without Ni treatment were fabricated. I-V and noise characteristics of these devices were then investigated. Comparing the GaN PDs with and without Ni treatment, it was found that GaN PDs prepared with Ni treatment can not only reduce dark current, but also enhance the UV-to-Vis rejection ratio. With an applied bias of -2 V, it was found that noise equivalent power (NEP) and detectivity (D*) for the PDs prepared without Ni treatment were 9.95 × 10^-8 W and 1.59 × 10⁷ cmHz^0.5W^-1, respectively. At the same applied bias, it was also found that NEP and D* for PDs prepared with Ni treatment were 1.74 × 10^-11 W and 9.07 × 10¹⁰ cmHz^0.5W^-1, respectively.