Photovoltaic measurements in carbon nanotube - Amorphous silicon core/shell nanowire

Carbon nanotube is one of the promising materials for exploring new concepts in solar energy conversion and photon detection. Here, we report the first experimental realization of a single core/shell nanowire photovoltaic device (2-4μm) based on carbon nanotube and amorphous silicon. Specifically, a multi-walled carbon nanotube (MWNTs) was utilized as the metallic core, on which n-type and intrinsic amorphous silicon layers were coated. A Schottky junction was formed by sputtering a transparent conducting indium-tin-oxide layer to wrap the outer shell of the device. The single coaxial nanowire device showed typical diode ratifying properties with turn-on voltage around 1V and a rectification ratio of 104 when biased at ±2V. Under illumination, it gave an open circuit voltage of ∼0.26V. Our study has shown a simple and useful platform for gaining insight into nanowire charge transport and collection properties. Fundamental studies of such nanowire device are important for improving the efficiency of future nanowire solar cells or photo detectors. © 2012 IEEE.

Band alignment between Ta2O5 and metals for resistive random access memory electrodes engineering

Band alignment of resistive random access memory (RRAM) switching material Ta2O5 and different metal electrode materials was examined using high-resolution X-ray photoelectron spectroscopy. Schottky and hole barrier heights at the interface between electrode and Ta2O 5 were obtained, where the electrodes consist of materials with low to high work function (Φ m, v a c from 4.06 to 5.93 eV). Effective metal work functions were extracted to study the Fermi level pinning effect and to discuss the dominant conduction mechanism. An accurate band alignment between electrodes and Ta2O5 is obtained and can be used for RRAM electrode engineering and conduction mechanism study. © 2013 American Institute of Physics.

Nanoplasmonics for guiding, focusing and detection applications

In this talk we demonstrate configurations and devices that allow plasmonic assisted guiding and confinement of electromagnetic energy at the nanoscale. We also demonstrate silicon plasmonic Schottky detector for telecom wavelengths. © 2011 OSA.

Nanoplasmonics for guiding, focusing and detection applications

In this talk we demonstrate configurations and devices that allow plasmonic assisted guiding and confinement of electromagnetic energy at the nanoscale. We also demonstrate silicon plasmonic Schottky detector for telecom wavelengths. ©2011 Optical Society of America.

Compact Reconfigurable Binary-Decision-Diagram Logic Circuit on a GaAs Nanowire Network

We describe a reconfigurable binary-decision-diagram logic circuit based on Shannon's expansion of Boolean logic function and its graphical representation on a semiconductor nanowire network. The circuit is reconfigured by using programmable switches that electrically connect and disconnect a small number of branches. This circuit has a compact structure with a small number of devices compared with the conventional look-up table architecture. A variable Boolean logic circuit was fabricated on an etched GaAs nanowire network having hexagonal topology with Schottky wrap gates and SiN-based programmable switches, and its correct logic operation together with dynamic reconfiguration was demonstrated.

Electric tunable of electron spin polarization in hybrid magnetic-electric barrier structures

Electron spin-dependent transport properties have been theoretically investigated in two-dimensional electron gas (2DEG) modulated by the magnetic field generated by a pair of anti-parallel magnetization ferromagnetic metal stripes and the electrostatic potential provided by a normal metal Schottky stripe. It is shown that the energy positions of the spin-polarization extremes and the width of relative spin conductance excess plateau could be significantly manipulated by the electrostatic potential strength and width, as well as its position relative to the FM stripes. These interesting features are believed useful for designing the electric voltage controlled spin filters. (C) 2008 Elsevier B.V. All rights reserved.

Photoelectric characteristics of metal/InGaN/GaN heterojunction structure

A heterojunction structure photodetector was fabricated by evaporating a semitransparent Ni/Au metal film oil the InGaN/GaN structure. The photocurrent (PC) spectra show that both the Schottky junction (NiAu/InGaN) and the InGaN/GaN isotype heterojunction contribute to the PC signal which suggests that two junctions are connected in series and result in a broader spectral response of the device. Secondary electron, cathodoluminescence and electron-beam-induced current images measured from the same area of the edge surface clearly reveal the profile of the layer structure and distribution of the built-in electric field around the two junctions. A band diagram of the device is drawn based oil the consideration of the polarization effect at the InGaN/GaN interface. The analysis is consistent with the physical mechanism of a tandem structure of two junctions connected in series.

Influence of electron irradiation on hydrothermally grown zinc oxide single crystals

The resistivity of hydrothermally grown ZnO single crystals increased from similar to 10(3) Omega cm to similar to 10(6) Omega cm after 1.8 MeV electron irradiation with a fluence of similar to 10(16) cm(-2), and to similar to 10(9) Omega cm as the fluence increased to similar to 10(18) cm(-2). Defects in samples were studied by thermally stimulated current (TSC) spectroscopy and positron lifetime spectroscopy (PLS). After the electron irradiation with a fluence of 10(18) cm(-2), the normalized TSC signal increased by a factor of similar to 100. A Zn vacancy was also introduced by the electron irradiation, though with a concentration lower than expected. After annealing in air at 400 degrees C, the resistivity and the deep traps concentrations recovered to the levels of the as-grown sample, and the Zn vacancy was removed.

Effect of p-GaN layer thickness on the performance of p-i-n structure GaN ultraviolet photodetectors

We investigated the influence of thickness of p-GaN layer on the performance of p-i-n structure GaN ultraviolet photodetector. Through the simulation calculation, it was found that both the quantum efficiency and dark current of device decrease when employing thicker p-GaN layer, while both the quantum efficiency and dark current increase with decreasing thickness of p-GaN layer. It is suggested that the Schottky contact junction between the metal and p-GaN may be responsible for the incompatible effect. We has to make a suitable choice of the thickness of p-GaN in the device design according to the application requirement.

Hydrogen sensors based on AlGaN/AIN/GaN HEMT

Pt/AlGaN/AIN/GaN high electron mobility transistors (HEMT) were fabricated and characterized for hydrogen sensing. Pt and Ti/Al/Ni/Au metals were evaporated to form the Schottky contact and the ohmic contact, respectively. The sensors can be operated in either the field effect transistor (FET) mode or the Schottky diode mode. Current changes and time dependence of the sensors under the FET and diode modes were compared. When the sensor was operated in the FET mode, the sensor can have larger current change of 8 mA, but its sensitivity is only about 0.2. In the diode mode, the current change was very small under the reverse bias but it increased greatly and gradually saturated at 0.8 mA under the forward bias. The sensor had much higher sensitivity when operated in the diode mode than in the FET mode. The oxygen in the air could accelerate the desorption of the hydrogen and the recovery of the sensor. (c) 2007 Elsevier Ltd. All rights reserved.

Photovoltaic effects in InGaN structures with p-n junctions

InGaN photovoltaic structures with p-n junctions have been fabricated by metal organic chemical vapour deposition. Using double-crystal X-ray diffraction measurements, it was found that the room temperature band gaps of p-InGaN and n-InGaN films were 2.7 and 2.8 eV, respectively. Values of 3.4 x 10(-2) mA cm(-2) short-circuit current, 0.43 V open-circuit voltage and 0.57 fill factor have been achieved under ultraviolet illumination (360 nm), which were related to p-n junction connected back-to-back with a Schottky barrier and many defects of the p-InGaN film. 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fabrication and transport properties of ZnO/Nb-1 wt %-doped SrTiO3 epitaxial heterojunctions

(110) ZnO/(001) Nb-1 wt %-doped SrTiO3 n-n type heteroepitaxial junctions were fabricated using the pulse laser deposition method. A diodelike current behavior was observed. Different from conventional p-n junctions or Schottky diodes, the diffusion voltage was found to increase with temperature. At all temperatures, the forward current was perfectly fitted on the thermionic emission model. The band bending at the interface can qualitatively explain our results, and the extracted high ideality factor at low temperatures, as well as large saturation currents, is ascribed to the deep-level-assisted tunneling current through the junction. (C) 2008 American Institute of Physics.

Determination of the relative permittivity of the AlGaN barrier layer in strained AlGaN/GaN heterostructures

Using the measured capacitance-voltage curves and the photocurrent spectrum obtained from the Ni Schottky contact on a strained Al0.3Ga0.7N/GaN heterostructure, the value of the relative permittivity of the AlGaN barrier layer was analysed and calculated by self-consistently solving Schrodinger's and Poisson's equations. It is shown that the calculated values of the relative permittivity are different from those formerly reported, and reverse biasing the Ni Schottky contact has an influence on the value of the relative permittivity. As the reverse bias increases from 0 V to - 3 V, the value of the relative permittivity decreases from 7.184 to 7.093.

Effect of silver growth temperature on the contacts between Ag and ZnO thin films

Highly c-axis oriented ZnO thin films were deposited on Si substrates by the pulsed laser deposition (PLD) method. At different growth temperatures, 200 nm silver films as the contact metal were deposited on the ZnO thin films. The growth temperatures have great influence on the crystal quality of Ag films. Current-voltage characteristics were measured at room temperature. The Schottky contacts between Ag and ZnO thin films were successfully obtained when silver electrodes were deposited at 150A degrees C and 200A degrees C. Ohmic contacts were formed while the growth temperatures were lower than 150A degrees C or higher than 200A degrees C. After analysis, the forming of Ag/ZnO Schottky contacts was shown to be dependent on the appearance of the p-type inversion layer at the interface between Ag and ZnO layers.

A Fully Integrated 900-MHz Passive RFID Transponder Front End With Novel Zero-Threshold RF-DC Rectifier

This paper presents a fully integrated CMOS analog front end for a passive 900-MHz radio-frequency identification (RFID) transponder. The power supply in this front end is generated from the received RF electromagnetic energy by using an RF-dc voltage rectifier. In order to improve the compatibility with standard CMOS technology, Schottky diodes in conventional RF-dc rectifiers are replaced by diode-connected MOS transistors with zero threshold. Meanwhile, theoretical analyses for the proposed rectifier are provided and verified by both simulation and measurement results. The design considerations of the pulsewidth-modulation (PWM) demodulator and the backscatter modulator in the front end are also discussed for low-power applications. The proposed front end is implemented in a 0.35-mu m 2P4M CMOS technology. The whole chip occupies a die area of 490 x 780 mu m(2) and consumes only 2.1 mu W in reading mode under a self-generated 1.5-V supply voltage. The measurement results show that the proposed rectifier can properly operate with a - 14.7-dBm input RF power at a power conversion efficiency of 13.0%. In the proposed RFID applications, this sensitivity corresponds to 10.88-m communication distance at 4-W equivalent isotropically radiated power from a reader base station.