| 21. |
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| 22. |
- Wang, Qin, et al.
(författare)
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Analysis of surface oxides on narrow bandgap III-V semiconductors leading towards surface leakage free IR photodetectors
- 2012
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 8353, s. 835311-
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Tidskriftsartikel (refereegranskat)abstract
- Narrow bandgap semiconductors GaSb, InAs, and InSb are important building blocks for infrared photodetectors based on type-II InSb quantum dots or an InAs/GaSb strained layer superlattice. Understanding the surface chemical composition of these materials can provide valuable information that enables optimization of device surface passivation techniques leading towards surface leakage free IR photodetectors. We report on an investigation into Ga-, In-, Sb-, and As-oxides and other chemical species on the surface of untreated, dry etched and thermally treated GaSb, InAs and InSb samples by x-ray photoelectron spectroscopy. The experimental results reveal the presence of Sb- and Ga-oxides on the surfaces of the untreated and treated GaSb samples. Both Sb- and In-oxides were observed on the surface of all InSb samples, and especially the dry etched sample had thicker oxide layers. In the case of the InAs samples, not only In-and As-oxides XPS signals were obtained, but also AsCl species were found on the ICP dry etched sample. These results helped to analyze the dark current of our fabricated IR detectors.
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| 23. |
- Wang, Qin, et al.
(författare)
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MWIR interband transitions in type-II (III) In(GaAl)Sb quantum dots
- 2015
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Konferensbidrag (refereegranskat)abstract
- In this work we present an alternative approach for realizing desired IR devices with appropriate operating wavelengths in the MWIR region utilizing In(GaAl)Sb quantum dots embedded in an InAs matrix grown by MBE. The QDs exhibit spatially indirect interband transitions in a type-II broken bandgap alignment, with a transition energy that can be tuned by bandgap and strain engineering utilizing either the quantum dot size or the incorporation of Ga or (GaAl) into the QDs. Furthermore, the growth of such QDs does not require sophisticated epitaxial designs needed for superlattices or quantum cascade structures regarding large numbers of alternating layers and very exact interfaces. The QD structures are expected to exhibit key advantages for IR devices e.g. higher operating temperature, lower power consumption, size, weight, and cost. The structural and composition properties of designed and grown In(GaAl)Sb QDs were characterized using AFM, SEM, TEM, and XRD. The corresponding optical properties, both in terms of absorption and emission, were analyzed and compared for selected QD samples before and after annealing at 650 °C.
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| 24. |
- Wang, Qin, et al.
(författare)
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Surface states characterization and simulation of type-II In(Ga)Sb quantum dot structures for processing optimization of LWIR detectors
- 2013
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 9780819494955
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Konferensbidrag (refereegranskat)abstract
- Quantum structures base on type-II In(Ga)Sb quantum dots (QDs) embedded in an InAs matrix were used as active material for achieving long-wavelength infrared (LWIR) photodetectors in this work. Both InAs and In(Ga)Sb are narrow band semiconductor materials and known to possess a large number of surface states, which apparently play significant impact for the detector's electrical and optical performance. These surface states are caused not only by material or device processing induced defects but also by surface dangling bonds, oxides, roughness and contaminants. To experimentally analyze the surface states of the QD structures treated by different device fabrication steps, atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) measurements were performed. The results were used to optimize the fabrication process of the LWIR photodetectors in our ongoing project. The dark current and its temperature dependence of the fabricated IR photodetectors were characterized in temperature range 10 K to 300 K, and the experiment results were analyzed by a theoretic modeling obtained using simulation tool MEDICI.
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| 25. |
- Zhao, Ming, et al.
(författare)
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Molecular beam epitaxy growth of Si/SiGe bound-to-continuum quantum cascade structures for THz emission
- 2008
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 517:1, s. 34-37
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Tidskriftsartikel (refereegranskat)abstract
- A Si/SiGe bound-to-continuum quantum cascade design for THz emission was grown using solid-source molecular beam epitaxy on Si0.8Ge0.2 virtual substrates. The growth parameters were carefully studied and several samples with different boron doping concentrations were grown at optimized conditions. Extensive material characterizations revealed a high crystalline quality of the grown structures with an excellent growth control. Layer undulations resulting from a nonuniform strain field, introduced by high doping concentration, were observed. The device characterizations suggested that a modification on the design was needed in order to enhance the THz emission.
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| 26. |
- Zhao, Ming, et al.
(författare)
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Strain-symmetrized Si/SiGe multi-quantum well structures grown by molecular beam epitaxy for intersubband engineering
- 2006
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Ingår i: Journal of luminescence. - : Elsevier BV. - 0022-2313. ; 121:2, s. 403-408
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Tidskriftsartikel (refereegranskat)abstract
- Three strain-symmetrized Si/SiGe multi-quantum well structures, designed for probing the carrier lifetime of intrawell intersubband transitions between heavy hole 1 (HH1) and light hole 1 (LH1) states with transition energies below the optical phonon energy, were grown by molecular beam epitaxy at low temperature on fully relaxed SiGe virtual substrates. The grown structures were characterized by using various experimental techniques, showing a high crystalline quality and very precise growth control. The lifetime of the LH1 excited state was determined directly with pump-probe spectroscopy. The measurements indicated an increase of the lifetime by a factor of 2 due to the increasingly unconfined LH1 state, which agreed very well with the design. It also showed a very long lifetime of several hundred picoseconds for the holes excited out of the well to transit back to the well through a diagonal process.
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