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  1. International Collaboration project: The interface effects in HgCdTe infrared optoelectronic material and devices,

  The University of Western Australia and Shanghai Institute of Technical Physics, (CNSF60811120169)

  This project will undertake a fundamental investigation interfaces and quantum structures in molecular beam epitaxy (MBE) grown HgCdTe semiconductor materials and devices. HgCdTe (an alloy of CdTe and HgTe) is the most sensitive IR detector material known, with unique optoelectronic and structural properties that are attractive for IR focal plane arrays, ultra-sensitive single detectors and tunable sensors for wavelengths from 1um to greater than 25um. These properties include high IR absorption, low electron effective mass, low Auger recombination, tunable bandgap (by changing the ratio, x of CdTe to HgTe), and near constant lattice parameter over the entire range of x. As a result, HgCdTe is of significant importance for IR detection in security, mineral exploration, environmental monitoring and biological and chemical sensing for commercial as well as related uses. The advent of HgCdTe MBE growth (a relatively recent advance) has made available many new bandgap-engineered materials and device structures. A common factor that has limited the application of these new structures has been high interface state densities, both at surfaces and at internal heterojunction interfaces, and 1/f noise performance. Recent work indicates that these limitations may be related.

  In this project optoelectronic properties of MBE grown HgCdTe infrared structures will be studied at the quantum level both theoretically and experimentally. In the theoretical work, first-principles methods will be used to study the structures, including interfaces (both surfaces and internal heterointerfaces), impurity structures and energy states, and to determine their effects on the optoelectronic behaviour of HgCdTe materials and devices, including 1/f noise. Experimental work will include investigation of statistical carrier transport behaviour at p-n junctions and interfaces development of a new infrared modulation spectroscopy technology to study interband transition behaviour in HgCdTe quantum structures. Using these data, the parameters for the HgCdTe material and interfaces will be extracted for device modeling. The comprehensive range of tools and expertise needed to undertake this work is only possible because of the collaboration between the two institutes involved in this project, which will allow investigation into the fundamental origins of interface states in HgCdTe materials, and develop techniques to mitigate their effects in MBE grown photodiode structures.

  2. International Collaboration project: The self-heating effect and electrical characterization of GaN-based MOS-HEMTs, (SH2008B116)

  Purdue University, USA and Shanghai Institute of Technical Physics, China

  Different static interface trap and charge densities created at the AlGaN/Al2O3 interface are considered in the output characteristics. The effect of the gate and source/drain extension lengths on both the output performance and self-heating is discussed in detail, allowing for device optimization. The dissipated Joule electric power causes the self-heating effects, which lead to negative differential output conductance. Hot electrons make a negligible contribution to the negative differential output conductance in our long channel MOS-HEMTs. The self-heating is also strongly affected due to the fluctuation of the interface states. By designing and optimization of GaN-based MOS-HEMTs, the measurements decreasing hot electron and current collapse effects for GaN-based MOS-HEMTs are discussed in detail supplying device optimization with theoretical references. The simulated drain lag characteristics are in good agreement with reported experimental data. The trapped charges may accumulate at the drain-side gate edge, where the electric field significantly changes and gate-to-drain-voltage-dependent strain is induced, causing a notable current collapse. Quantum-well MOS-HEMTs have been proposed and demonstrated for device optimization. The simulations confirm that better electron localization can dramatically reduce current collapse.


  [1] W. D. Hu, X. S. Chen, Z. J. Quan, X. M. Zhang, Y. Huang, C. S. Xia, W. Lu, and P. D. Ye, Simulation and optimization of GaN-based metal-oxide-semiconductor high-electron-mobility-transistor using field-dependant drift velocity model, Journal of Applied Physics, 102, 034502 (2007).

  [2] W. D. Hu, X. S. Chen, Z. J. Quan, C. S. Xia, W. Lu, and P. D. Ye, Self-heating simulation of GaN-based metal-oxide-semiconductor high-electron-mobility transistors including hot electron and quantum effects, Journal of Applied Physics, 100, 074501 (2006).

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