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So far xiangyu has created 91 blog entries.

Theoretical considerations on efficiency degradation due to thermal effect in a planar GaN-based LED with a GaN substrate

In this paper, using a fully-coupled, three-dimensional electro-thermal device simulator, we study the mechanism of efficiency degradation at high current operation in planar GaN-based light emitting diodes (LED). In particular, the improvement of the efficiency degradation using thicker conductive GaN substrates has been demonstrated. First, it is found that local Joule heating inside thin conductive [...]

December 11th, 2018|

An optical study of the D—D neutron irradiation-induced defects in Co- and Cu-doped ZnO wafers

Room-temperature photoluminescence and optical transmittance spectroscopy of Co-doped (1 × 1014, 5 × 1016, and 1 × 1017 cm−2) and Cu-doped (5 × 1016 cm−2) ZnO wafers irradiated by D—D neutrons (fluence of 2.9 × 1010 cm−2) have been investigated. After irradiation, the Co or Cu metal and oxide clusters in doped ZnO wafers are [...]

December 4th, 2018|

Realization of Low Dislocation GaN/Sapphire Wafers by 3-Step Metalorganic Vapor Phase Epitaxial Growth with Island Induced Dislocation Control

A novel dislocation reducing mechanism was successfully introduced into the conventional 2-step metalorganic vapor phase epitaxial (MOVPE) growth method of GaN/sapphire wafer by inserting an additional intermediate-temperature (IT)-GaN buffer between the low-temperature (LT)-GaN buffer and the main high-temperature (HT)-GaN layer. During the growth of the IT-GaN buffer, high-density islands with faceted slopes were formed. Vertically [...]

November 26th, 2018|

Electrical impedance tomography applied to semiconductor wafer characterization

A new method is described for determining the distribution of resistivity of semiconductor wafers and thin conducting films. It uses peripheral electrodes to inject small direct currents into the wafer or film and to measure the resultant potential differences, from which the distribution of resistivity is calculated. The usable area of the wafer is not [...]

November 22nd, 2018|

Characterization of Interface in GaAs Epitaxial Wafer by Spatially Resolved Photoluminescence from Cleaved Face

We characterized the interface between the epitaxial layer and substrate of a GaAs wafer by measuring the microscopic photoluminescence (PL) on the cleaved face of the wafer. The intensity of the band-edge PL was higher in the epitaxial layer than in the substrate and locally decreased at the interface. This finding indicates that the non-radiative [...]

November 14th, 2018|

Fabrication of through-wafer 3D microfluidics in silicon carbide using femtosecond laser

We demonstrate a prototype through-wafer microfluidic structure in bulk silicon carbide (SiC) fabricated by femtosecond laser micromachining. The effects of laser fluence and scanning speed on the laser-affected zone are also investigated. Furthermore, the wettability of the laser-affected surface for the target liquid, mineral oil, is examined. Microchannels of various cross-sectional shapes are fabricated by [...]

November 7th, 2018|

Nanoscale transport properties at silicon carbide interfaces

Wide bandgap semiconductors promise devices with performances not achievable using silicon technology. Among them, silicon carbide (SiC) is considered the top-notch material for a new generation of power electronic devices, ensuring the improved energy efficiency required in modern society. In spite of the significant progress achieved in the last decade in the material quality, there [...]

September 13th, 2018|

Single crystalline and core–shell indium-catalyzed germanium nanowires—a systematic thermal CVD growth study

Germanium nanowires were synthesized using thermal chemical vapor deposition (CVD) and indium as a catalyst. The process parameter space for successful growth was studied. By optimizing the growth temperature and gas pressure, high aspect ratio germanium nanowires have been obtained. Scanning electron microscopy investigations indicate that the final diameter of the nanowires is strongly influenced [...]

September 5th, 2018|

Growth related aspects of epitaxial nanowires

We use metal–organic vapour phase epitaxy for growth investigations of epitaxial nanowires in III–V materials, such as GaAs, GaP, InAs, and InP. In this paper we focus on gold assisted growth of nanowires. The nature of the metal particle—whether it is in the solid or liquid state—is discussed. For InAs and InP we have demonstrated [...]

August 29th, 2018|

Highly aligned, template-free growth and characterization of vertical GaN nanowires on sapphire by metal–organic chemical vapour deposition

We report the growth of exceptionally well aligned and vertically oriented GaN nanowires on  r-plane sapphire wafers via metal–organic chemical vapour deposition. The nanowires were grown without the use of either a template or patterning. Transmission electron microscopy indicates the nanowires are single crystalline, free of threading dislocations, and have triangular cross-sections. The high degree of [...]

August 22nd, 2018|