Jia-Chuan Lin

Manufacturing method for n-type porous silicon based on Hall effect without illumination

A method for the fabrication of n-type porous silicon (n‐PS) is developed. The Hall effect is applied in the fabrication process. The majority carriers in n-type Si (electrons) are swept down by the Lorentz force. Enough holes continuously appear on the surface layer to participate in chemical reaction during the etching process. Illumination sources are not necessary in this method. Therefore, no illumination limit has to be concerned in the formation of deep PS layer. The morphology, porosity, and photoluminescence of the n‐PS prepared by the proposed method are investigated. Strong visible photoluminescence emissions are demonstrated on n‐PS at about 650nm.

White-light emissions from p-type porous silicon layers by high-temperature thermal annealing

In this study, the white-light emissions, including red, green and blue colors, appearing on the same porous silicon samples are originally introduced by a thermal-annealing method. The SEM, FTIR, and PL are discussed for different annealing temperature cases. The FTIR is used to monitor the chemical bonding structures of the PS samples under different annealing temperatures. The results show that the variation of chemical bonding relates to the variation of the emission wavelength. The emission intensities of the blue-green-light components are enhanced with the increase of annealing temperature. The PL spectra cover the entire visible region under the excitations of He-Cd laser beam, and a strong white-light emission can be observed by the naked eye at room temperature.

Photoluminescence from n-type porous silicon layer enhanced by a forward-biased np-junction

A new approach for the fabrication of n-type porous silicon layer is proposed. A hole-rich p-layer is arranged underneath the n-layer, and the np-junction is under forward biased condition in the etching process. Therefore sufficient holes can drift straight-upward and pass across the np-junction from p-region to n-region to participate in electrochemical reaction during the etching process with an unfailing supply. Illumination is an optional hole-supplier in this approach, so the problem of illumination-depth limitation can be overcome. Strong visible photoluminescence emissions are demonstrated on the hole-poor n-type porous layer at about 650 nm.

Light emission and negative differential conductance of n-type nanoporous silicon with buried p-layer assistance

The light-emission and current-voltage properties of n-type nanoporous silicon (n-NPS) with a hole assistance of buried p layer are explored. The influences of anodic current density on the formation, morphology, and properties of n-NPS are measured. Such n-NPS films have nanoscaled pores and high-aspect-ratio pillars. Since the anisotype junction is forward biased during the anodization process, many holes can drift straightupward from p layer and participate in the electrochemical reaction. At room temperature, high peak-to-valley current ratios of about 117.3 can be obtained in negative difference conductance region as well as strong visible light emissions are clearly observed under ultraviolet excitation.

Simulation and analysis of metamorphic high electron mobility transistors

In this paper, the metamorphic high electron mobility transistors (mHEMTs) are investigated numerically and compared with pseudo-morphic high electron mobility transistors (pHEMTs). The two-dimensional device simulator, MEDICI, is used to solve the Poissons equation and the electron/hole current continuity equations. The influences of @d-doping concentration and position, gate width, spacer thickness, etc. on the performances of HEMTs are explored. It shows clearly that mHEMTs have higher transconductances, drain currents and DC voltage swings than pHEMTs.

Preparation and optoelectronic properties of NiO/ZnO heterostructure nanowires

This study proposes the use of a ZnO-nanowire (ZnO-NW)-based heterojunction structure for applications of nano optoelectronic sensors and photovoltaic devices. Nano heterojunctions (NHJs) were formed via e-beam deposition of ptype nickel oxide (NiO) onto the vertical-aligned ZnO-NWs grown by hydro-thermal growth method. The dark J-V curve shows that the prepared NiO/ZnO-NWs NHJ has a diode-like behavior with a forward threshold voltage (Vth) of 1.2 V and a leakage current (Jr at -1V) of 0.02 μA/cm2, respectively. It also exhibits a superior response to UV (366 nm) and AM 1.5G light illuminations. The Vth and the photocurrents (i.e., Jr at -1V) under UV (366 nm @ 6 mW/cm2) and AM 1.5G light were 0.7 V/0.06 μA/cm2 and 0.5 V/ 3.2 μA/cm2, respectively, revealing an increase in the diode current of about 3× and 160×, respectively.

The fabrication of glucose sensor by nanoporous silicon film and its switching characteristics on visible color light response

An investigation of the visible light glucose sensor by utilized nanoporous (NPS) silicon material as a sensitive layer was proposed. In the experiments, all studied NPS films are prepared by electrochemical anodization technique and the obtained depth are about 3.3 μm. The peak of PL-intensity curve is 610 nm under normal air condition. Based on its high surface to volume ratio (SVR) and unique light emission properties, the studied NPS glucose sensor has a high sensitivity and stability. The visible light response on the film surface switches obviously between distinct colors with/without glucose treatment. As compared with conventional electronic glucose sensor, the highly sensitive and obvious light switching characteristics would be important to related detection. It has a potential application on small-size, low-cost, portable and electric-free sensor systems. After the immersion treatment of 1M glucose solution on the studied NPS samples, an obvious blue-shift behavior of PL-feature (from 610 to 560 nm) is observed at room temperature. The color switching can be read by a naked-eye easily.

High Field-Emission Stability of Offset-Thin-Film Transistor-Controlled Al-Doped Zinc Oxide Nanowires

Aluminum-doped zinc oxide (AZO) nanowire (NW) arrays incorporating an offset thin-film transistor (offset-TFT) have been proposed to achieve high field-emission (FE) stability. The AZO NW field emission arrays (FEAs) were hydrothermally grown at a low temperature of 85 °C. The uncontrolled AZO NW FEAs demonstrated superior FE characteristics (i.e., turn-on field of ~2.17 V/µm and threshold field of ~3.43 V/µm) compared with those of the conventional CNT FEAs grown at a temperature below 600 °C. However, uncontrolled AZO NW FEAs show a larger current fluctuation of 15.6%. Therefore, the offset-TFTs were used to control the AZO NW FEAs. Consequently, the fluctuation of AZO NW FEAs could be significantly reduced to less than 2%. This novel field emission device exhibits good emission stability, low-voltage controllability, low-temperature processing, and structural simplicity, making it promising for applications in flat panel displays.

Thermal sensors based on nano porous silicon

In this study, the thermal properties of silicon samples with surfaces of porous and geometrical formation were reported. The etching methods of anodization chemical and heated KOH were utilized to perform the studied nano porous silicon (NPS) and pyramidal, respectively. Compared with usual surface formation of ordinary silicon sample, the larger surface to volume ratios were obtained from the fabricated NPS and pyramidal silicon devices. For the thermal applications such as thermal sensor and microheater, the etching profiles and surface to volume ration of studied were clarified by SEM measurement. Furthermore, the differential scanning calorimetry (DSC) was used to evaluate the thermal dissipation properties of studied samples.

Preparation of ZnO nanowires/p-GaN nanoheterojunction arrays and their optoelectric characteristics under UV and solar lights

One dimensional (1D) heterojunction arrays with high-density well-aligned ZnO nanowires (ZnO NWs) on p-type semiconductor has been demonstrated to be potential building blocks for photovoltaic (PV) and photodetecting devices applications due to its direct/wide bandgap and th e oriented geometry which provides a high carrier collection efficiency [1–6]. In this paper, we present the synthesis of vertically aligned ZnO NWs on a p-type gallium nitride (GaN) layer by using a n easy hydrothermal method to form ZnO NW/p-GaN nano heterojunction (NHJ) arrays f or optoelectronic devices applications. The optoelectronic properties of the ZnO NWs/p-GaN N HJs wi th good UV sensitivities and superior PV performances under an UV (366 nm) light and a simulated AM1.5G so lar illumination were reported. Effects of t he length of ZnO NW s on the PV performance of the ZnO NWs/p-GaN NH Js were also investigated and discussed.