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Li W.,CAS Institute of Semiconductors | Wang X.,CAS Institute of Semiconductors | Wang X.,Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices | Wang X.,ISCAS XJTU Joint Laboratory of Functional Materials and Devices for Informatics | And 7 more authors.
Journal of Alloys and Compounds | Year: 2014

The high electron mobility transistor (HEMT) structure employing novel InxAl1-xN/AlN multiple-quantum-wells (MQWs) as barrier layer is presented. The two-dimensional electron gas (2DEG) characteristics of (InxAl1-xN/AlN) MQWs/GaN heterojunction have been investigated by solving coupled Schrödinger and Poisson equations self-consistently. The influence of AlN thickness, InxAl1-xN thickness, In content and pair number of (InxAl1- xN/AlN)MQWs on sheet carrier density is investigated. AlN thickness dependence of carriers in barrier layer to total carriers in HEMT and In 0.18Al0.82N conduction band diagrams are discussed. The sheet carrier density of (In0.18Al0.82N/AlN)MQWs/GaN heterojunction is larger than that of (AlxGa1 -xN/GaN)SLs/GaN heterojunction and achieves to as large as 3.59 × 1013 cm-2 with AlN thickness of 1.4 nm, barrier thickness of 15 nm and pair number of 5. The calculation shows that (In0.18Al0.82N/AlN)MQWs provide high barrier which confines the 2DEG effectively. © 2014 Elsevier B.V. All rights reserved.


Deng Q.,CAS Institute of Semiconductors | Wang X.,CAS Institute of Semiconductors | Wang X.,ISCAS XJTU Joint Laboratory of Functional Materials and Devices for Informatics | Xiao H.,CAS Institute of Semiconductors | And 9 more authors.
Journal of Physics D: Applied Physics | Year: 2011

The conversion efficiency of InxGa1-xN/GaN multiple quantum well solar cells is originally investigated in theory based on the ideal diode model and the ideal unity quantum well model. The results reveal that the conversion efficiency partially depends on the width of the quantum well and the thickness of the barrier region but is dominated by the number of quantum wells and indium content of InxGa1-xN. The calculated results are found to be basically trustworthy by comparing with reported experimental results. An In0.15Ga0.85N/GaN multiple quantum well solar cell is successfully fabricated with a conversion efficiency of 0.2%. The main discrepancy between calculated and experimental results is the material quality and manufacturing technology which need to be improved. © 2011 IOP Publishing Ltd.


Peng E.,CAS Institute of Semiconductors | Wang X.,CAS Institute of Semiconductors | Wang X.,ISCAS XJTU Joint Laboratory of Functional Materials and Devices for Informatics | Xiao H.,CAS Institute of Semiconductors | And 7 more authors.
Journal of Crystal Growth | Year: 2013

High electron mobility transistors (HEMTs) structures with GaN, Al 0.025Ga0.975N and Al0.04Ga0.96N high resistivity (HR) buffers were grown on sapphire by metal organic chemical vapor deposition (MOCVD). The structural and electrical properties of these three samples were investigated and compared. By increasing Al composition of AlGaN buffer, full width at half maximum (FWHM) values of (0002) and (10-12) x-ray rocking curves for buffer increase, indicating higher threading dislocation density. Room temperature noncontact Hall measurements were performed, and the measured 2DEG mobility was 1828 cm2/V s for GaN buffer, 1728 cm 2/V s for Al0.025Ga0.975N buffer, and 1649 cm2/V s for Al0.04Ga0.96N buffer, respectively. Combining the theoretical calculation with the experiments, it was demonstrated that the decrease of mobility was attributed to higher dislocation density in sample with higher Al composition of AlGaN buffer. Devices were fabricated and it was found that the double heterojunction (DH) HEMT with Al 0.025Ga0.975N buffer could effectively reduce the buffer leakage current. © 2013 Elsevier B.V.


Deng Q.,CAS Institute of Semiconductors | Wang X.,CAS Institute of Semiconductors | Wang X.,ISCAS XJTU Joint Laboratory of Functional Materials and Devices for Informatics | Yang C.,CAS Institute of Semiconductors | And 8 more authors.
Physica B: Condensed Matter | Year: 2011

In this work, the structure of InxGa1-xN/GaN quantum dots solar cell is investigated by solving the Schrdinger equation in light of the KronigPenney model. Compared to pn homojunction and heterojunction solar cells, the InxGa1-xN/GaN quantum dots intermediate band solar cell manifests much larger power conversion efficiency. Furthermore, the power conversion efficiency of quantum dot intermediate band solar cell strongly depends on the size, interdot distance and gallium content of the quantum dot arrays. Particularly, power conversion efficiency is preferable with the location of intermediate band in the middle of the potential well. © 2010 Elsevier B.V.All rights reserved.


Ding J.,CAS Institute of Semiconductors | Wang X.,CAS Institute of Semiconductors | Wang X.,ISCAS XJTU Joint Laboratory of Functional Materials and Devices for Informatics | Xiao H.,CAS Institute of Semiconductors | And 5 more authors.
Physica B: Condensed Matter | Year: 2012

We present numerical optimization of carrier confinement characteristics in (Al xGa 1-xN/AlN)SLs/GaN heterostructures in the presence of spontaneous and piezoelectrically induced polarization effects. The calculations were made using a self-consistent solution of the Schrödinger, Poisson, potential and charge balance equations. It is found that the sheet carrier density in GaN channel increases nearly linearly with the thickness of AlN although the whole thickness and equivalent Al composition of Al xGa 1-xN/AlN superlattices (SLs) barrier are kept constant. This result leads to the carrier confinement capability approaches saturation with thicknesses of AlN greater than 0.6 nm. Furthermore, the influence of carrier concentration distribution on carrier mobility was discussed. Theoretical calculations indicate that the achievement of high sheet carrier density is a trade-off with mobility. © 2012 Elsevier B.V. All rights reserved.


Ding J.,CAS Institute of Semiconductors | Wang X.,CAS Institute of Semiconductors | Wang X.,ISCAS XJTU Joint Laboratory of Functional Materials and Devices for Informatics | Xiao H.,CAS Institute of Semiconductors | And 5 more authors.
Journal of Alloys and Compounds | Year: 2012

We present calculations of carrier confinement characteristics in (Al yGa 1-yN/AlN)SLs/GaN/(In xGa 1-xN/GaN) MQW/GaN heterojunction structure in the presence of spontaneous and piezoelectrically induced polarization effects. The calculations were made using a self-consistent solution of the Schrödinger, Poisson, potential and charge balance equations. An optimization of In xGa 1-xN/GaN multiquantum-well (MQW) was made firstly including thickness of GaN channel, InGaN, and indium composition of In xGa 1-xN in order to increase carrier density and mobility, and the influence of pairs of AlGaN/AlN superlattices (SLs) and InGaN/GaN MQWs on structure was discussed. Theoretical calculations clearly indicate that the two-dimensional electron gas (2DEG) sheet carrier density in designed heterostructure is greatly increased due to the enhancing of carrier confinement compared to those in conventional AlGaN/GaN one at the similar Al composition. Furthermore, the calculated carrier distribution shows that carrier mobility will be improved by reducing interface roughness and alloy disorder scattering in designed heterostructure. © 2012 Elsevier B.V.


Li Z.,CAS Institute of Semiconductors | Xiao H.,CAS Institute of Semiconductors | Wang X.,CAS Institute of Semiconductors | Wang X.,ISCAS XJTU Joint Laboratory of Functional Materials and Devices for Informatics | And 5 more authors.
Physica B: Condensed Matter | Year: 2013

In this study, potential efficiency of InGaN/Si mechanically stacked two-junction solar cell is theoretically investigated by optimizing the band gap and thickness of the top InGaN cell. Results show that the optimum conversion efficiency is 35.2% under AM 1.5 G spectral illuminations, with the bandgap and thickness of top InGaN solar cell are 2.0 eV and 600 nm, respectively. The results and discussion would be helpful in designing and fabricating high efficiency InGaN/Si mechanically stacked solar cell in experiment. © 2013 Elsevier B.V. All rights reserved.


Wan X.-J.,CAS Institute of Semiconductors | Wang X.-L.,CAS Institute of Semiconductors | Wang X.-L.,ISCAS XJTU Joint Laboratory of Functional Materials and Devices for Informatics | Wang X.-L.,Xi'an Jiaotong University | And 9 more authors.
Chinese Physics Letters | Year: 2013

The valence band offset (VBO) of an Al0.17Ga0.83N/GaN heterojunction is determined to be 0.13 ± 0.07 eV by x-ray photoelectron spectroscopy. From the obtained VBO value, the conduction band offset (CBO) of ∼0.22 eV is obtained. The results indicate that the Al0.17Ga0.83N/GaN heterojunction exhibits a type-I band alignment. © 2013 Chinese Physical Society and IOP Publishing Ltd.


Peng E.,CAS Institute of Semiconductors | Wang X.,CAS Institute of Semiconductors | Wang X.,ISCAS XJTU Joint Laboratory of Functional Materials and Devices for Informatics | Xiao H.,CAS Institute of Semiconductors | And 7 more authors.
Journal of Alloys and Compounds | Year: 2013

This is a theoretical study of AlGaN/AlN/GaN/AlGaN double heterojunction (DH) structure with AlGaN as buffer layer. Our calculation shows that as the buffer Al content increases, though two-dimensional electron gas (2DEG) sheet density decreases, the channel back-barrier caused by polarization-induced electric field in GaN provides better electron confinement. And under certain conditions the DH-structure shows bipolar characteristics, with an additional two-dimensional hole gas (2DHG) formed at GaN/AlGaN interface. The influence of the buffer Al content and GaN channel thickness on the 2DEG and 2DHG sheet densities are investigated, and the conditions for the disappearance of 2DHG are discussed. Also, the mobility inhibited by dislocation scattering is enhanced in DH-structure due to the enhancement of screening effect of the 2DEG. © 2013 Elsevier B.V. All rights reserved.


Kang H.,CAS Institute of Semiconductors | Wang Q.,CAS Institute of Semiconductors | Xiao H.-L.,CAS Institute of Semiconductors | Wang C.-M.,CAS Institute of Semiconductors | And 10 more authors.
Chinese Physics Letters | Year: 2014

Lateral Schottky barrier diodes (SBDs) on AlGaN/GaN heterojunctions are fabricated and studied. The characteristics of the fabricated SBDs with different Schottky contact diameters and different Schottky-Ohmic contact spacings are investigated. The breakdown voltage can be increased by either increasing the Schottky-Ohmic contact spacing or increasing the Schottky contact diameter. However, the specific on-resistance is increased at the same time. A high breakdown voltage of 1400 V and low reverse leakage current below 20nA are achieved by the device with a Schottky contact diameter of 100 μm and a contact spacing of 40 μm, yielding a high V2BR/RON,sp value of 194 MW.cm-2. © 2014 Chinese Physical Society and IOP Publishing Ltd.

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