Tsung-Hsien Kao

ZnO-Based Ultraviolet Photodetectors With Novel Nanosheet Structures

This study presents the fabrication of ZnO nanosheets on a glass substrate using a room-temperature (approximately 25 °C) solution method. The average length and diameter of the ZnO nanosheets were 1.2 μm and approximately 5 nm, respectively. The ultraviolet (UV)-to-visible rejection ratio of the sample is approximately 42 when biased at 1 V, and the fabricated UV photodetector is visible-blind with a sharp cutoff at 370 nm. The transient time constants measured during the rise time and fall time were τr = 5.37 s and 6.02 s, respectively. The low-frequency noise spectra obtained from the UV photodetector were caused purely by the 1/ f noise. The noise-equivalent power and normalized detectivity ( D^*) of the ZnO nanosheet photodetector were 6.12 × 10 ^-9W and 2.17 × 10 ⁹ cm·Hz ^0.5 W ^-1, respectively.

Low-Frequency Noise Characteristics of In-Doped ZnO Ultraviolet Photodetectors

We report the growth of vertically aligned indium-doped ZnO (IZO) nanorods on a glass substrate using a low-temperature hydrothermal method. An IZO nanorod metal-semiconductor-metal (MSM) ultraviolet (UV) photodetector (PD) was also fabricated. It was found that the UV-to-visible rejection ratio of the fabricated PD was ~109 when biased at 1 V with a sharp cutoff at 390 nm. With an incident light wavelength of 390 nm and an applied bias of 1 V, it was found that measured responsivity of the PD was 2.5 A/W. Furthermore, it was also found that the noise equivalent power and detectivity of the fabricated IZO nanorod MSM PD were 1.42×10-10 W and 1.44×1011 cm·Hz0.5·W-1, respectively.

Novel Ga-ZnO Nanosheet Structures Applied in Ultraviolet Photodetectors

Vertically aligned Ga-doped ZnO (GZO) nanosheets were grown on a glass substrate using a low-temperature (90 °C) hydrothermal method. The average length and diameter of the nanosheets were ~720 and 26 nm, respectively. The GZO nanosheets exhibited wurtzite and monoclinic structures. A metal-semiconductor-metal ultraviolet (UV) photodetector (PD) was also fabricated for the GZO nanosheets. Results revealed that the photoresponses of the GZO UV PD were flat at short wavelengths. Meanwhile, a sharp cutoff was observed at 340 nm. The UV-to-visible rejection ratio of the fabricated PD was ~89 at 1 V bias voltage.

Noise Properties of Ag Nanoparticle-Decorated ZnO Nanorod UV Photodetectors

A novel and simple hydrothermal method was performed to synthesize vertically aligned Ag nanoparticle (NP)-decorated ZnO nanorods (NRs) on a seed layer/glass substrate. At an applied bias of 0.2 V and incident light wavelength of 380 nm, the measured fabricated photodetector (PD) responsivity value was ~12.4 A/W, whereas the corresponding UV to visible rejection ratio was ~4478. In addition, the noise equivalent power and corresponding detectivities of the fabricated Ag NPdecorated ZnO NR metal-semiconductor-metal (MSM) PD were 4.85 × 10^-11 W and 2.72 × 10¹¹ cm · Hz^0.5 · W^-1, respectively.

The Effect of Ga Doping Concentration on the Low-Frequency Noise Characteristics and Photoresponse Properties of ZnO Nanorods-Based UV Photodetectors

This study investigates the control of Ga doping in ZnO nanorods (NRs) grown on an amorphous ZnO-seeded glass substrate through hydrothermal method. ZnO was doped with various Ga concentrations (0.25, 0.5, and 1 mM). The average lengths of the resulting NRs were approximately 2.36, 1, and 1.5 μm, respectively, and the average diameters were 123, 78, and 117 nm, respectively. In addition, Ga-doped ZnO (GZO) NR-based ultraviolet photodetectors (PDs) with a sharp cutoff at 370 nm were fabricated. With an applied voltage of 1 V, different Ga precursor solution concentrations of 0.25, 0.5, and 1 mM yielded measured device responsitivities of 2.2 × 10^-2, 14.9, and 14.1 A/W, respectively. The Ga concentration can be used to control the responsivity of the fabricated PDs. Furthermore, the measured noise equivalent power of the PDs at 0.25, 0.5, and 1 mM were 1.06 × 10^-9, 3.13 × 10^-11, and 1.29 × 10 ^-10 W, respectively. The corresponding detectivities of the GZO NR PDs were measured at 1.24 × 10 ¹⁰, 4.21 × 10¹¹ W, and 1.01 × 10¹¹ cm·Hz^0.5·W ^-1, respectively.

Trap properties of high-k/metal gate pMOSFETs with aluminum ion implantation by random telegraph noise and 1/f noise measurements

In this study, the impact of aluminum ion implantation on 1/f noise characteristics and random telegraph noise (RTN) in high-k/metal gate (HK/MG) p-type metal–oxide–semiconductor field-effect transistors (pMOSFETs) was investigated. Aluminum ion implantation (Al I/I) into TiN/HfO2/SiO2 was implemented to tune an effective work function (EWF) in pMOSFETs without EOT increase complicated processes. RTN and 1/f results revealed that regardless of the implanted dose, HK/MG devices with Al I/I exhibit lower slow oxide trap densities than the control devices, which are responsible for the reduced trap position (xt) from the SiO2 interfacial layer (IL)/Si interface. For the HK/MG devices with different implanted doses, no significant differences in trap properties were observed.

Impact of Aluminum Ion Implantation on the Low Frequency Noise Characteristics of Hf-Based High- \(k\) /Metal Gate pMOSFETs

The impact of aluminum ion implantation (Al I/I) on the 1/f noise and random telegraph noise (RTN) characteristics of high-k/metal gate (HK/MG) pMOSFETs is investigated. The Al I/I technology was implemented to tune the effective work function (EWF) of pMOSFETs without increasing the equivalent oxide thickness and complicating the process. The RTN and 1/f noise results showed that irrespective of the implanted dose, the HK/MG devices with Al I/I still exhibit lower slow oxide trap densities for the control device, because the Al filled the defect and formed a thin Al2O3 layer. In addition, for the HK/MG devices with different implanted doses, no significant differences in the trap properties are noted. However, the modulated EWF can be attributed to the Al I/I-induced dipoles at the HfO2/SiO2 interface.

Nonvolatile organic transistor-memory devices based on pentacene semiconductors and poly (methyl methacrylate)/graphene quantum-dot composite trap layers

Summary form only given. In this study, we have demonstrated nonvolatile memory devices using poly (methyl methacrylate) (PMMA)/grapheme quantum-dots (GQDs) trap layers with pentacene semiconductor channel. A strong memory effect was also found in the entacene-based OTFTs and the electrical characteristics were improved by introducing the PMMA/GQDs composite layer. PMMA/GQDs memory achieved a larger memory window, higher on/off current ratio and lower subthreshold swing than that of PMMA memory. Moreover, the PMMA/GQDs memory has well switching cycle performance. In this study, it suggests the exciting potential of PMMA/GQDs trap layers to be used for a highly promising material in non-volatile memory devices. In addition, the process for fabricating nonvolatile memory devices was based on simple solution processes and organic semiconductor/charge trapping layers.

Low-Frequency Noise Spectra of Laterally Bridged ZnO Microrod-Based Photodetectors

The laterally bridged ZnO microrods grown from an Au electrode applied to metal-semiconductor-metal photodetector was fabricated. Interlaced ZnO microrods with approximate single-crystalline structure can be grown from Au electrode fingers. The dark-current was 5.00 × 10^-5 A with an applied voltage of 1 V. Highly dense lateral ZnO microrod-based photodetectors produce remarkable responsivity of 1.93 × 10⁵ A/W. Moreover, an extremely high internal photoconductive gain of 6.28 × 10⁵ exists in the fabricated photodetectors. For a given bandwidth of 10 kHz and 1 V applied bias, the noise equivalent power of photodetectors were estimated to be 1.86 × 10^-13 W, and correspond to normalized detectivity of 1.12 × 10¹² cm·Hz^0.5 W^-1. This result may be attributed to an internal photoconductive gain mechanism and high-density bridged ZnO microrods. Our approach provides a simple and seed-layer-free method to fabricate high-performance ultraviolet photodetectors.

Investigation of trap properties in high-k/metal gate p-type metal-oxide-semiconductor field-effect-transistors with aluminum ion implantation using random telegraph noise analysis

In this study, the impact of aluminum ion implantation (Al I/I) on random telegraph noise (RTN) in high-k/metal gate (HK/MG) p-type metal-oxide-semiconductor field-effect-transistors (pMOSFETs) was investigated. The trap parameters of HK/MG pMOSFETs with Al I/I, such as trap energy level, capture time and emission time, activation energies for capture and emission, and trap location in the gate dielectric, were determined. The configuration coordinate diagram was also established. It was observed that the implanted Al could fill defects and form a thin Al2O3 layer and thus increase the tunneling barrier height for holes. It was also observed that the trap position in the Al I/I samples was lower due to the Al I/I-induced dipole at the HfO2/SiO2 interface.