Shi-Ming Peng

Characteristic Improvements of ZnO-Based Metal–Semiconductor–Metal Photodetector on Flexible Substrate with ZnO Cap Layer

In this work, ZnO-based metal–semiconductor–metal photodetectors with and without a ZnO cap layer were fabricated on flexible substrates of poly(ethylene terephthalate) (PET) for comparative analysis. The ZnO films were prepared by a low-temperature sputtering process. The photodetector with a ZnO cap layer (stack structure: ZnO/Ag/ZnO/PET) shows a much higher UV-to-visible rejection ratio of 1.56 ×103 than that without. This can be attributed to the photocurrents that are not only significantly increased in the UV region but also slightly suppressed in the visible region for such a novel structure. With an incident wavelength of 370 nm and an applied bias of 3 V, the responsivities of both photodetectors with and without a ZnO cap layer are 3.80 ×10-2 and 2.36 ×10-3 A/W, which correspond to quantum efficiencies of 1.13 and 0.07%, respectively. The Schottky barrier height at the Ag/ZnO interface is also determined to be 0.782 eV.

Semitransparent Field-Effect Transistors Based on ZnO Nanowire Networks

This investigation demonstrates the fabrication of semitransparent field-effect transistors with self-assembling ordered ZnO nanowire (NW) networks, using a high-k HfO₂ gate. The devices exhibit excellent optical transparency and transistor performance at on/off ratios of >;10⁵, a mobility of ~7.59 cm² V^-1 s^-1, and threshold voltages of 4 V. Under UV illumination (3.65 eV), the devices exhibit the highest relative photoconductivity (2.08 10^5), corresponding to a photoresponsivity of 3.96 A/W at low operating voltages ( V_GS = 0 V and V_DS = 1 V). The result suggests that the NW-based devices have low power consumption and high photosensivity when used in photodetection.

Photoelectrical and Noise Characteristics of ZnO Nanowire Networks Photosensor

This study describes the photoresponse and noise characteristics of UV photosensors with ZnO nanowire networks. The fabrication approach, which combines conventional photolithography with sidewall nucleation sites, achieves site specificity and the self-assembly of an ordered ZnO nanowire networks. The photoresponse of the device is approximately three orders of magnitude, because the high surface-to-volume ratio enables efficient light absorption. These results reveal that the reproducible photocurrent response, high-photosensivity, internal gain and detectivity suggest that the device has potential applications in UV photodetection.

Transparent ZnO Nanowire-Network Ultraviolet Photosensor

This paper demonstrates the fabrication of transparent ultraviolet (UV) photosensors with a self-assembling ordered ZnO nanowired network. The average optical transmission of the entire networked photosensor structure in the visible range of the spectrum is about 70%. At an applied bias of 5 V and 340-nm irradiation, the photoresponsivity and the ratio of UV-to-visible rejection was 175.58 and 207.63 A/W for the transparent UV photosensors. For a bandwidth of 100 Hz and an applied bias of 5 V, the noise equivalent power and normalized detectivity of the devices were 2.32 × 10-10 W and 4.36 × 108 cm · Hz0.5/W , respectively.

Ultraviolet photodetectors based on MgZnO thin films

In this work, Ti/Au Ohmic contacts to both Mg0.24Zn0.76O and ZnO film-based metal-semiconductor-metal (MSM) photodetectors (PDs) were fabricated on glass substrates for comparative analysis. The transmittance spectra measured around the optical energy gap revealed that Mg0.24Zn0.76O films have a larger optical energy gap (3.54 eV) than ZnO films (3.25 eV). Mg0.24Zn0.76O MSM-structured ultraviolet (UV) PDs show a much higher UV-to-visible rejection ratio of 2.78×103 than those made of ZnO films. This can be attributed to the low dark current (0.08 pA) of the Mg0.24Zn0.76O UV PDs and the small full width at half maximum (0.34°) of the Mg0.24Zn0.76O (002) x-ray diffraction peak, indicating better crystal quality than that of ZnO. With an applied bias of 5 V and illuminations at 350 and 380 nm, the Mg0.24Zn0.76O and ZnO film-based MSM PDs exhibited responsivities of 0.4 and 0.32 A/W, respectively.

Photosensitivity of Field-Effect Transistors Based on ZnO Nanowire Networks

Self-assembling ordered ZnO nanowire (NW) network-based field-effect transistors (FETs) were fabricated by bottom-up photolithography. The devices had on/off ratios of >; 104, mobilities of ~1.31 cm2 V-1 s-1, mobilities of and threshold voltages of ~-1 V. Under UV treatment (340 nm, 57.46 ), the devices exhibited relative photoconductivity ratio increases of at a depletion state of 8 V gate bias (1.56 × 103 A/V). The fabricated FETs exhibit a broad range of electrical characteristics because of variation in the contact quality of the metal/NW, the dielectric/NW, and the NW/NW interfaces. However, the fabricated approach offers a cost-effective route to integrate self-assembled ZnO NW network-based FETs.

Electrical and Photosensivity Characteristics of Hybrid/Composite ZnO Nanorod Transistors

This letter shows the bottom-contact-type transistors with free-standing ZnO NR arrays that were fabricated by hydrothermal decomposition. The NR arrays were selectively grown in the channel layer between the source and drain electrodes in order to enhance the electrical characteristics of the hybrid/composite NR transistors. The on/off current ratio and mobility of hybrid/composite NR transistors (3.98 × 10⁵; 0.66 cm²·V^-1·s^-1) are higher than those of the ZnO film transistors (2.2 × 10⁴; 0.29 cm²·V^-1·s^-1). The relative photoconductivity (γ) and photoresponsivity (<i>R</i>) of hybrid/composite NR transistors (γ_NR = 4.6 × 10⁵; <i>R</i> = 0.2 A/W) performed better than conventional film transistors (γ_film = 2.27 × 10²; <i>R</i> = 1.06 × 10^-3 A/W) in the depletion region (<i>V</i>_DS = -19 V; <i>V</i>_GS = 50 V ).