Zheng You-Dou

Au/Pt/InGaN/GaN Heterostructure Schottky Prototype Solar Cell

A patterned Au/Pt/In0.2Ga0.8N/GaN heterostructure Schottky prototype solar cell is fabricated. The forward current-voltage characteristics indicate that thermionic emission is a dominant current transport mechanism at the Pt/InGaN interface in our fabricated cell. The Schottky solar cell has an open-circuit voltage of 0.91 V, short-circuit current density of 7mA/cm2, and fill factor of 0.45 when illuminated by a Xe lamp with a power density of 300 mW/cm2. It exhibits a higher short-circuit current density of 30 mA/cm2 and an external quantum efficiency of over 25% when illuminated by a 20-mW-power He-Cd laser.

Chemical mechanical polishing of freestanding GaN substrates

Chemical mechanical polishing (CMP) has been used to produce smooth and scratch-free surfaces for GaN. In the aqueous solution of KOH, GaN is subjected to etching. At the same time, all surface irregularities, including etch pyramids, roughness after mechanical polishing and so on will be removed by a polishing pad. The experiments had been performed under the condition of different abrasive particle sizes of the polishing pad. Also the polishing results for different polishing times are analyzed, and chemical mechanical polishing resulted in an average root mean square (RMS) surface roughness of 0.565 nm, as measured by atomic force microscopy.

Optical and Magnetic Properties of Fe-Doped GaN Diluted Magnetic Semiconductors Prepared by MOCVD Method

Fe-doped GaN thin films are grown on c-sapphires by metal organic chemical vapour deposition method (MOCVD). Crystalline quality and phase purity are characterized by x-ray diffraction and Raman scattering measurements. There are no detectable second phases formed during growth and no significant degradation in crystalline quality as Fe ions are doped. Fe-related optical transitions are observed in photoluminescence spectra. Magnetic measurements reveal that the films show room-temperature ferromagnetic behaviour. The ferromagnetism may originate from carrier-mediated Fe-doped GaN diluted magnetic semiconductors or nanoscale iron clusters and Fe-N compounds which we have not detected.

Effects of interface traps in silicon-quantum-dots-based memory structures

Abstract Effects of interface traps in silicon-quantum-dots(Si-QDs) based memory structures have been investigated using capacitance–voltage measurement. The observations demonstrate that both the interface traps at Si-QDs and the interface states at SiO 2 /Si-substrate have strong influences on the charge storage characteristics. The observed long-term charge retention behavior is analyzed in terms of direct charge-tunneling from deep trapping centers at Si-QDs to the interface states at SiO 2 /Si-substrate, considering three-dimensional quantum confinement and Coulomb charging effects.

Polyaniline / silicon heterojunctions

Abstract The p-n and p-p polyaniline PAn/Si heterojunctions have been prepared and investigated. It is demonstrated experimentally that the p-n PAn/si heterojunction is a fine rectifying junction with obvious photoelectrical characteristics, and the barrier of the p-n PAn/Si heterojunction is mostly concentrated at the surface of Si. The interface states located at 1/3 E g in the band gap of Si play important roles in the p-n PAn/Si heterojuction. The operation principle of the conducting polymer PAn/Silicon heterojunction is different from that of conventional heterojunction consisting of two kinds of inorganic semiconductors.

Field plate engineering for GaN-based Schottky barrier diodes

The practical design of GaN-based Schottky barrier diodes (SBDs) incorporating a field plate (FP) structure necessitates an understanding of their working mechanism and optimization criteria. In this work, the influences of the parameters of FPs upon breakdown of the diode are investigated in detail and the design rules of FP structures for GaN-based SBDs are presented for a wide scale of material and device parameters. By comparing three representative dielectric materials (SiO2, Si3N4 and Al2O3) selected for fabricating FPs, it is found that the product of dielectric permittivity and critical field strength of a dielectric material could be used as an index to predict its potential performance for FP applications.

Properties of Fe/Si heterostructure grown by MOCVD

An Fe film was grown on an Si(100) substrate by metalorganic chemical vapor deposition (MOCVD) using thermal decomposition of iron pentacarbonyl, Fe(CO)5. The X-ray diffraction and cross-sectional high resolution electron microscopy (HREM) show that the Fe deposited film is a single crystal Fe film on Si(100). Single crystal Fe/Si Schottky barrier diodes exhibit good rectification.

Surface morphology and composition studies in InGaN/GaN film grown by MOCVD

InGaN films were deposited on (0001) sapphire substrates with GaN buffer layers under different growth temperatures by metalorganic chemical vapor deposition. The In-composition of InGaN film was approximately controlled by changing the growth temperature. The connection between the growth temperature, In content, surface morphology and defect formation was obtained by X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy (AFM). Meanwhile, by comparing the SEM and AFM surface morphology images, we proposed several models of three different defects and discussed the mechanism of formation. The prominent effect of higher growth temperature on the quality of the InGaN films and defect control were found by studying InGaN films at various growth temperatures.

Photoresponse of the In0.3Ga0.7N metal–insulator–semiconductor photodetectors

In 0.3Ga 0.7N metal–insulator–semiconductor (MIS) and metal–semiconductor (MS) surface barrier photodetectors have been fabricated. The In0.3Ga0.7N epilayers were grown on sapphire by metalorganic chemical vapour deposition (MOCVD). The photoresponse and reverse current–voltage characteristics of the In0.3Ga0.7N MIS and MS photodetectors were measured. A best zero bias responsivity of 0.18 A/W at 450 nm is obtained for the In0.3Ga0.7N MIS photodetector with 10 nm Si3N4 insulator layer, which is more than ten times higher than the In0.3Ga0.7N MS pho-todetector. The reason is attributed to the decrease of the interface states and increase of surface barrier height by the inserted insulator. The influence of the thickness of the Si3N4 insulator layer on the photoresponsivity of the MIS photodetector is also discussed.

High-quality ZnO growth, doping, and polarization effect

The authors have reported their recent progress in the research field of ZnO materials as well as the corresponding global advance. Recent results regarding (1) the development of high-quality epitaxy techniques, (2) the defect physics and the Te/N co-doping mechanism for p-type conduction, and (3) the design, realization, and properties of the ZnMgO/ZnO hetero-structures have been shown and discussed. A complete technology of the growth of high-quality ZnO epi-films and nano-crystals has been developed. The co-doping of N plus an iso-valent element to oxygen has been found to be the most hopeful path to overcome the notorious p-type hurdle. High mobility electrons have been observed in low-dimensional structures utilizing the polarization of ZnMgO and ZnO. Very different properties as well as new physics of the electrons in 2DEG and 3DES have been found as compared to the electrons in the bulk.