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| 3. |
- Eriksson, Martin. O., et al.
(författare)
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The Dynamics of Charged and Neutral Excitons in an InGaN Quantum Dot on a GaN Pyramid
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The neutral (X0) and negatively charged excitons (X-) in an InGaN QD on a GaN pyramid is studied by the timeintegrated micro-photoluminescence (μPL) and time-resolved micro-photoluminescence (TRμPL) microcopies. Both X0 and X- exhibit mono-exponential decay curves with fitted lifetimes of 310 and 140 ps, respectively. Neither energy shifts nor changes in the life times X0 and X- with increasing excitation power were observed, indicating the QD is small and free from the quantum confine Stark effect. The TRμPL is not only a powerful technique for studying the dynamics of exciton in QDXs, but also for the identification of exciton complexes in QDs.
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| 4. |
- Fagerlind, Martin, 1980, et al.
(författare)
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Influence of gate position on dispersion characteristics of GaN HEMTs
- 2008
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Ingår i: WOCSDICE 2008, Abstract book. ; , s. 99-100
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Konferensbidrag (refereegranskat)abstract
- GAN HEMTs with varying design have been fabricated to optimize device performance. The focus of this report is the minimization of drain current dispersion by the variation of the electric field distribution. In this work this is done by varying the placement of the gate and to some extent varying gate length and length of the gate connected field plate. We present pulsed IV characteristics for a number of different device designs.
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| 5. |
- Fagerlind, Martin, 1980, et al.
(författare)
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Investigation of the interface between silicon nitride passivations and AlGaN/AlN/GaN heterostructures by C(V) characterization of metal-insulator-semiconductor-heterostructure capacitors
- 2010
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 108:1
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Tidskriftsartikel (refereegranskat)abstract
- Capacitance-voltage [C(V)] measurements of metal-insulator-semiconductor-heterostructure capacitors are used to investigate the interface between silicon nitride passivation and AlGaN/AlN/GaN heterostructure material. AlGaN/AlN/GaN samples having different silicon nitride passivating layers, deposited using three different deposition techniques, are evaluated. Different interface state distributions result in large differences in the C(V) characteristics. A method to extract fixed charge as well as traps from the C(V) characteristics is presented. Rough estimates of the emission time constants of the traps can be extracted by careful analysis of the C(V) characteristics. The fixed charge is positive for all samples, with a density varying between 1.3 x 10(12) and 7.1 x 10(12) cm(-2). For the traps, the peak density of interface states is varying between 16 x 10(12) and 31 x 10(12) cm(-2) eV(-1) for the three samples. It is concluded that, of the deposition methods investigated in this report, the low pressure chemical vapor deposited silicon nitride passivation shows the most promising results with regards to low densities of interface states. (C) 2010 American Institute of Physics. [doi:10.1063/1.3428442]
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| 6. |
- Forsberg, Urban, et al.
(författare)
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Improved hot-wall MOCVD growth of highly uniform AlGaN/GaN/HEMT structures
- 2009
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 311:10, s. 3007-3010
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Tidskriftsartikel (refereegranskat)abstract
- The inherent advantages of the hot-wall metal organic chemical vapor deposition (MOCVD) reactor (low temperature gradients, less bowing of the wafer during growth, efficient precursor cracking) compared to a cold-wall reactor make it easier to obtain uniform growth. However, arcing may occur in the growth chamber during growth, which deteriorates the properties of the grown material. By inserting insulating pyrolytic BN (PBN) stripes in the growth chamber we have completely eliminated this problem. Using this novel approach we have grown highly uniform, advanced high electron mobility transistor (HEMT) structures on 4 semi-insulating (SI) SiC substrates with gas-foil rotation of the substrate. The nonuniformities of sheet resistance and epilayer thickness are typically less than 3% over the wafer. The room temperature hall mobility of the 2DEG is well above 2000 cm(2)/V s and the sheet resistance about 270 Omega/sqr.
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| 8. |
- Henry, Anne, et al.
(författare)
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AlGaN Multiple Quantum Wells and AlN Grown in a Hot-wall MOCVD for Deep UV Applications
- 2009
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Ingår i: ECS Transactions, Vol. 25, Iss. 8. - : ECS. - 9781566777452 ; , s. 837-844
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Konferensbidrag (refereegranskat)abstract
- AlxGa1-xN multiple quantum wells (MQW) were grown on AlN epilayer grown on 4H-SiC substrate. The growth was performed without interruption in a horizontal hot-wall MOCVD reactor using a mixture of hydrogen and nitrogen as carrier gases. The precursors were ammonia, trimethylaluminum and trimethylgallium. Results obtained from X-ray diffraction and infra-red reflectance were used to obtain the composition of the films when growing simple AlxGa1 xN layer. Visible reflectance was used to evaluate the thickness of the films. Finally the MQW parameters as thicknesses and composition variation were obtained by scanning transmission electron microscopy and demonstrated an agreement with the growth parameters used
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| 9. |
- Henry, Anne, et al.
(författare)
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Large area mapping of the alloy composition of AlxGa1-xN using infrared reflectivity
- 2009
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Ingår i: PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS. - : Wiley. - 1862-6254. ; 3:5, s. 145-147
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Tidskriftsartikel (refereegranskat)abstract
- The energy position of a dip observed in the IR-reflectance spectra recorded from wurtzite c-plane AlxGa1-xN epitaxial films grown on SiC substrate reflects the composition of the alloy. A calibration procedure is presented with the possibility of mapping for large area wafer. The technique is non-destructive, scalable and fast. The limitations are discussed and comparisons with other techniques are made.
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| 10. |
- Holtz, Per Olof, et al.
(författare)
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Deterministic Single InGaN Quantum Dots grown on GaN Micro-Pyramid Arrays
- 2013
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Ingår i: Advanced Materials Research. - : Trans Tech Publications Inc.. - 1022-6680 .- 1662-8985. ; 646, s. 34-37
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- InGaN quantum dots (QDs) formed on top of GaN pyramids have been fabricated by means of selective area growth employing hot wall MOCVD. Upon regrowth of a patterned substrate, the growth will solely occur in the holes, which evolve into epitaxially grown wurtzite based pyramids. These pyramids are subsequently overgrown by a thin optically active InGaN well. The QDs are preferably nucleating at the apices of the pyramids as evidenced by the transmission electron microscopy (TEM). The emission from these QDs have been monitored by means of microphotoluminescence (µPL), in which single emission lines have been detected with a sub-meV line width. The µPL measurements undoubtedly reveal that the QDs are located in the apexes of the pyramids, since the sharp emission peaks can only be monitored as the excitation laser is focused on the apices in the µPL. It is also demonstrated that the emission energy can be changed in a controlled way by altering the growth conditions, like the growth temperature and/or composition, for the InGaN layers. The tip of the GaN pyramid is on the nm scale and can be made sharp or slightly truncated. TEM analysis combined with µPL results strongly indicate that the Stranski-Krastanow growth modepreferably is taking place at the microscopic c-plane truncation of the GaN pyramid. Single emission lines with a high degree of polarization is a common feature observed for individual QDs. This emission remains unchanged with increasing the excitation power and sample temperature. An in-plane elongated QD forming a shallow potential with an equal number of electrons and holes is proposed to explain the observed characteristics of merely a single exciton emission with a high degree of polarization.
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