SwePub - sökning: WFRF:(Monemar Bo 1942 )

Numrering	Referens	Omslagsbild	Hitta
1.	Bergman, Peder, 1961-, et al. (författare) Radiative recombination in InGaN/GaN multiple quantum well 2000 Ingår i: ICSCRM 99,1999. ; , s. 1571- Konferensbidrag (refereegranskat)
2.	Gogova, Daniela, et al. (författare) Growth and characterization of free-standing HVPE GaN on two-step epitaxial lateral overgrown GaN template 2005 Konferensbidrag (refereegranskat)
3.	Harati Zadeh, Hamid, 1964-, et al. (författare) Photoluminescence study of Si-doped GaN/Al0.07Ga0.93N multiple quantum wells with different dopant position 2004 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 84:25, s. 5071-5073 Tidskriftsartikel (refereegranskat)abstract The Si-doped GaN/Al0.07Ga0.93N multiple quantum wells (MQW) were investigated, using photoluminescence (PL) and time-resolved (PL) measurements. The influence of Si doping on the emission energy and recombination dynamics of the MWQs were also investigated, with different dopant position in the wells. It was observed that the redshifted emission of the MQWs was attributed to the self-energy shift of the electron states due to the correlated motion of the electrons exposed to the fluctuating potential of the donor ions. It was also observed that the PL decay time of the sample was ∼760 ps, at low temperature.
4.	Kasic, A., et al. (författare) Characterization of crack-free relaxed GaN grown on 2″ sapphire 2005 Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 98:7, s. 73525- Tidskriftsartikel (refereegranskat)abstract We demonstrate the growth of high-quality and virtually strain-free bulklike GaN by hydride vapor-phase epitaxy in a vertical atmospheric-pressure reactor with a bottom-fed design. The 300‐μm-thick GaN layer was grown on a 2″ (0 0 0 1) sapphire substrate buffered with a ∼ 2‐μm-thick GaN layer grown by metal-organic chemical-vapor deposition. During the cool down process to room temperature, cracking was induced in the sapphire substrate, thereby allowing the bulklike GaN layer to relax without provoking cracking of itself. The crystalline quality and the residual strain in the 2″ GaN wafer were investigated by various characterization techniques. The lateral homogeneity of the wafer was monitored by low-temperature photoluminescence mapping. High-resolution x-ray diffraction and photoluminescence measurements proved the high crystalline quality of the material grown. The position of the main near-band-gap photoluminescence line and the phonon spectra obtained from infrared spectroscopic ellipsometry show consistently that the 2″ crack-free GaN is virtually strain-free over a diameter of approximately 4 cm.
5.	Monemar, Bo, 1942-, et al. (författare) Defect related issues in the "current roll-off" in InGaN based light emitting diodes 2007 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91, s. 181103-1-181103-3 Tidskriftsartikel (refereegranskat)abstract Defect related contributions to the reduction of the internal quantum efficiency of InGaN-based multiple quantum well light emitting diodes under high forward bias conditions are discussed. Screening of localization potentials for electrons is an important process to reduce the localization at high injection. The possible role of threading dislocations in inducing a parasitic tunneling current in the device is discussed. Phonon-assisted transport of holes via tunneling at defect sites along dislocations is suggested to be involved, leading to a nonradiative parasitic process enhanced by a local temperature rise at high injection.
6.	Yakimova, Rositsa, 1942-, et al. (författare) Preface 2007 Ingår i: First International Symposium on Growth of Nitrides ISGN-1,2006. - Journal of Crystal Growth, Vol. 300 : Elsevier Science. Konferensbidrag (refereegranskat)
7.	Advances in Light emitting Materials 2008 Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract This special-topic volume‚ Advances in Light-Emitting Materials’, makes an important contribution to the field of silicon and III-nitride semiconductors. It begins with a brief history of visible-light emitting diodes. However, silicon is currently expanding from micro-electronics and into photonics. Due to its unsuitable band-gap, it has not previously been the material-of-choice for opto-electronic integration. That is now beginning to change and silicon devices have been developed which have the capability to emit, modulate, guide and detect light and which can be combined with microelectronics to form electronic and photonic integrated circuits. read more...In particular, the performance of silicon-based light-emitters has made rapid progress during the last few years: the first paper describes the potential value of the D-band luminescence caused by dislocations in silicon and its use in infra-red light-emitters. Silicon-wafer direct-bonding, which permits the controlled formation of dislocation networks, is described in detail in the next paper. Silicon and silicon-germanium light-emitting diodes (LED), which emit band-to-band radiation, are then described. This paper is followed by observations on the effect of carrier-confinement on the emission of the band-to-band radiation of LEDs fabricated in silicon-on-insulator form. Finally, MOS light-emitting devices, based upon rare-earth ion-implantation, are described. These structures exhibit efficient electroluminescence within the wavelengths ranging from UV to visible light.Altogether, this volume presents an in-depth review of this important topic.
8.	Arnaudov, B., et al. (författare) On the nature of the near bandedge luminescence of InN epitaxial layers 2005 Ingår i: AIP Conference Proceedings. - 0094-243X .- 1551-7616. ; 772, s. 285-286 Tidskriftsartikel (refereegranskat)
9.	Arnaudov, B., et al. (författare) Radiative recombination mechanism in highly modulation doped GaN/AlGaN multiple quantum wells 2006 Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - 1610-1634 .- 1610-1642. ; 6, s. 1888-1891 Tidskriftsartikel (refereegranskat)
10.	Arwin, Hans, 1950-, et al. (författare) Assessment of phonon mode characteristics via infrared spectroscopic ellipsometry on a-plane GaN 2005 Ingår i: ICSN-6,2005. Konferensbidrag (övrigt vetenskapligt/konstnärligt)
11.	Buyanova, Irina, 1960-, et al. (författare) Effect of electron irradiation on optical properties of gallium nitride 1999 Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T79, s. 72-75 Tidskriftsartikel (refereegranskat)abstract The effect of electron irradiation on the optical properties of GaN epilayers is studied in detail by photoluminescence (PL) spectroscopy. The most common types of GaN material are used, i.e. strained heteroepitaxial layers grown on 6H SiC or Al2O3 substrates, and thick bulk-like layers with the conductivity varying from n-type to semi-insulating and p-type. The main effects of electron irradiation on all investigated samples are found to be as follows: (i) a radiation-induced quenching of excitonic emissions in the near band gap region; (ii) an appearance of broad overlapping PL emissions within the spectral range 0.7-1.1 eV and (iii) the appearance of a PL band with a sharp no-phonon (NP) line at around 0.88 eV followed by a rich phonon assisted sideband. The 0.88 eV band is shown to originate from an internal transition of a deep defect. With increasing temperature a hot PL line can be observed at about 2-4 meV above the NP line, originating from higher lying excited states of the defect. The electronic structure of the 0.88 eV defect is shown to be very sensitive to the internal strain field in the GaN epilayers.
12.	Buyanova, Irina, 1960-, et al. (författare) Effect of Growth Conditions on the Photoluminescence of GaNAs/GaAs Quantum Structures 1999 Ingår i: Joint International Meeting the 196th Meeting of The Electrochemical Society ECS and the 1999 Fall Meeting of The Electrochemical Society of Japan ECSJ,1999. ; , s. 774- Konferensbidrag (övrigt vetenskapligt/konstnärligt)
13.	Buyanova, Irina, 1960-, et al. (författare) Effect of growth temperature on photoluminescence of GaNAs/GaAs quantum well structures 1999 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 75:24, s. 3781- Tidskriftsartikel (refereegranskat)abstract The effect of growth temperature on the optical properties of GaAs/GaNxAs1-x quantum wells is studied in detail using photoluminescence (PL) spectroscopies. An increase in growth temperature up to 580 °C is shown to improve the optical quality of the structures, while still allowing one to achieve high (>3%) N incorporation. This conclusion is based on: (i) an observed increase in intensity of the GaNAs-related near-band-edge emission; (ii) a reduction in band-edge potential fluctuations, deduced from the analysis of the PL line shape; and (iii) a decrease in concentration of some extended defects detected under resonant excitation of the GaNAs. The thermal quenching of the GaNAs-related PL emission, however, is almost independent of the growth temperature and is attributed to a thermal activation of an efficient nonradiative recombination channel located in the GaNAs layers.
14.	Buyanova, Irina, 1960-, et al. (författare) Electronic Properties of Ga(In)NAs Alloys 2001 Ingår i: MRS Internet Journal of Nitride Semiconductor Research. - 1092-5783. ; 6 Tidskriftsartikel (refereegranskat)abstract A brief review on the present knowledge of the electronic properties of the Ga(In)NAs ternary and quaternary alloys is given mainly from an experimental perspective. The discussion is focused on Ga(In)NAs with low N composition (< 10 %), where a large amount of experimental work has been done. Important fundamental electronic properties of the material system are analyzed with the emphasis on the nature of the giant band gap bowing in the alloy and nitrogen-induced modifications of the electronic structure of the conduction band. The current knowledge of the key material parameters, relevant for the device applications, such as electron effective mass, recombination processes and band alignment in Ga(In)NAs/GaAs heterostructures, is also reviewed.
15.	Buyanova, Irina, 1960-, et al. (författare) Electronic structure of the 0.88-eV luminescence center in electron-irradiated gallium nitride 1999 Ingår i: Physical review. B, Condensed matter and materials physics. ; 60:3, s. 1746-1751 Tidskriftsartikel (refereegranskat)abstract Photoluminescence (PL) spectroscopy is employed to determine the nature of a near-infrared PL emission with a no-phonon line at ∼0.88 eV, commonly present in electron-irradiated GaN. This PL emission is suggested to originate from an internal transition between a moderately shallow excited state (with an ionization energy ∼21 meV) and the deep ground state (with an ionization energy ∼900 meV) of a deep defect. The existence of a higher-lying second excited state related to the 0.88-eV PL center is also shown from temperature-dependent studies. A different electronic character of the wave functions related to the first and second excited states has been revealed by PL polarization measurements. Since the PL emission has been observed with comparable intensity in all electron-irradiated GaN samples independent of doping on the starting material, it is proposed that either native defects, or common residual contaminants or their complexes are involved. The substitutional ON donor (or related complex) is considered as the most probable candidate, based on the observed striking similarity in the local vibrational properties between the 0.88-eV PL centers and the substitutional OP donor in GaP.
16.	Buyanova, Irina, 1960-, et al. (författare) Mechanism for Light Emission in GaNAs/GaAs Structures Grown by Molecular Beam Epitaxy 1999 Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 216:1, s. 125-129 Tidskriftsartikel (refereegranskat)abstract A detailed photoluminescence (PL) study reveals that the low-temperature PL emission in GaNAs epilayers and GaAs/GaNxAs1 - x quantum well structures grown by molecular beam epitaxy is governed by recombination of localized excitons. This conclusion is based on the analysis of the PL lineshape, its dependence on the excitation power and measurement temperature, as well as PL transient data. The depth of the localization potential is estimated as about 60 meV, varying slightly among the different structures.
17.	Buyanova, Irina, 1960-, et al. (författare) Mechanism for low-temperature photoluminescence in GaNAs/GaAs structures grown by molecular-beam epitaxy 1999 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 75:4, s. 501- Tidskriftsartikel (refereegranskat)abstract The mechanism for low-temperature photoluminescence (PL) emissions in GaNAs epilayers and GaAs/GaNxAs1 - x quantum well (QW) structures grown by molecular-beam epitaxy is studied in detail, employing PL, PL excitation, and time-resolved PL spectroscopies. It is shown that even though quantum confinement causes a strong blueshift of the GaNAs PL emission, its major characteristic properties are identical in both QW structures and epilayers. Based on the analysis of the PL line shape, its dependence on the excitation power and measurement temperature, as well as transient data, the PL emission is concluded to be caused by a recombination of excitons trapped by potential fluctuations in GaNAs.
18.	Buyanova, Irina, 1960-, et al. (författare) On the spin injection in ZnMnSe/ZnCdSe heterostructures 2002 Konferensbidrag (refereegranskat)abstract We present results from a detailed study of spin injection in thin II-VI wide band gap semiconductor heterostructures by magnetooptical spectroscopy. It is shown that efficient spin alignment can be achieved in a diluted magnetic semiconductor barrier (a layer of ZnMnSe or ZnMnSe/CdSe superlattice) as thin as 10 nm. Rather efficient spin injection from such a thin spin aligner to a non-magnetic quantum well is demonstrated, even when the tunneling energy barrier is as thick as 10 nm. The effect of spin relaxation process on spin injection is also closely examined.
19.	Buyanova, Irina, 1960-, et al. (författare) Photoluminescence characterization of GaNAs/GaAs structures grown by molecular beam epitaxy 2000 Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 75:2-3, s. 166-169 Tidskriftsartikel (refereegranskat)abstract A number of optical spectroscopies, including photoluminescence (PL), PL excitation and cathodoluminescence, are employed for characterization of GaNAs epilayers and GaAs/GaNxAs1-x quantum well structures grown by gas source molecular beam epitaxy at low temperature. The existence of strong potential fluctuations in the band edge of the GaNAs alloy is concluded, even for the samples with high optical quality, from a detailed analysis of the characteristic properties of the GaNAs-related PL emission. Based on the observed similarity in the PL properties between the GaNAs epilayers and the QW structures, the potential fluctuations are suggested to be mainly due to composition disorder and strain nonuniformity of the alloy. ⌐ 2000 Elsevier Science S.A. All rights reserved.
20.	Buyanova, Irina, 1960-, et al. (författare) Photoluminescence Spectroscopy of the 0.88 eV Emission in Electron-Irradiated GaN 1999 Ingår i: APS March Meeting,1999. Konferensbidrag (övrigt vetenskapligt/konstnärligt)
21.	Buyanova, Irina, 1960-, et al. (författare) Resonant excitation spectroscopies of GaNAs/GaAs quantum structures 2000 Konferensbidrag (refereegranskat)abstract We employ resonant optical excitation and Raman spectroscopies to study optical properties of GaNAs-based quantum structures grown by gas source molecular beam epitaxy (GS MBE). Under above band gap non-resonant excitation the PL spectra of GaNAs are shown to be dominated by the commonly observed featureless localised exciton emission. In contrast, when excitation energy is tuned close to the band edge of GaNAs alloy a series of additional narrow lines can be detected in the PL spectra. The peak positions of these lines are at about 10 meV (strongest), and at 20, 32, and 36 below the excitation energy. The dominant 10 meV line can only be excited within very narrow spectral range coinciding with the free exciton emission in GaNAs. Based on performed spectral, temperature dependent, and polarization studies the strongest 10 meV and the weaker 20 meV lines are tentatively attributed to disorder activated Raman scattering which is strongly enhanced close to the mobility edge of the GaNAs. The 32 and 36 meV lines are, on the other hand, caused by Raman scattering involving GaAs-like TO and LO phonons.
22.	Buyanova, Irina, 1960-, et al. (författare) Tunable laser spectroscopy of spin injection in ZnMnSe/ZnCdSe quantum structures 2002 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:12, s. 2196- Tidskriftsartikel (refereegranskat)abstract Magneto-optical spectroscopy in combination with tunable laser excitation is employed to study exciton spin alignment and injection in ZnMnSe/ZnCdSe quantum structures. This approach enables us to selectively create preferred spin orientation and to separately monitor subsequent spin injection from individual spin states, thus shedding light on a possible source of spin loss. It is shown that the limited spin polarization in a nonmagnetic quantum well due to spin injection from a ZnMnSe-based diluted magnetic semiconductor (DMS) is not caused by a limited degree of spin alignment in the DMS, which is in fact complete, but rather occurs during subsequent processes.
23.	Chen, Weimin, 1959-, et al. (författare) Magneto-optical spectroscopy of defects in wide bandgap semiconductors : GaN and SiC 2000 Ingår i: Proceedings Conference on Optoelectronic and Microelectronic Materials and Devices. - : IEEE. - 0780366980 ; , s. 497-502 Konferensbidrag (refereegranskat)abstract We review recent progress in our understanding of intrinsic defects in GaN and SiC, gained from magneto-optical studies by Zeeman measurements and optically detected magnetic resonance. The two best-known intrinsic defects in these two wide bandgap semiconductors, i.e. the Ga interstitial in GaN and the silicon vacancy in SiC, are discussed in detail. The Ga interstitial is the first and only intrinsic defect in GaN that has so far been unambiguously identified, either in the presumably isolated form or in a family of up to three complexes. The silicon vacancy is among the most studied intrinsic defect in SiC, at least in two charge states, and yet still remains controversial.
24.	Chen, Weimin, 1959-, et al. (författare) Optical and Microwave Double Resonance of III-nitrides 1999 Ingår i: Joint International Meeting the 196th Meeting of The Electrochemical Society ECS and the 1999 Fall Meeting of The Electrochemical Society of Japan ECSJ,1999. ; , s. 764- Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
25.	Chen, Weimin, 1959-, et al. (författare) Optical Detection of Cyclotron Resonance (ODCR) in GaNAs/GaAs Quantum Well Structures 2000 Konferensbidrag (refereegranskat)abstract ODCR has been employed to study effective masses and carrier recombination in GaNAs/GaAs multi-quantum well (MQW) structures, prepared by MBE with the nitrogen composition up to 4.5 above GaAs bandgap excitation consists of the excitonic recombination within the GaNAs MQW, the band edge PL emissions from GaAs and a broad 0.8-eV PL of unknown origin. When monitoring these emissions under the above GaAs excitation, the ODCR spectrum is dominated by the electron and hole CR in GaAs, with effective mass values 0.07m0 and 0.5m_0, respectively. The ODCR mechanism is discussed in terms of hot carrier effects, resulting in a reduced carrier recombination in GaAs and an enhanced carrier trapping in the GaNAs MQW. Under resonant excitation of the GaNAs MQW only a broad ODCR signal can be observed corresponding to an effective mass value 0.1m_0, attributed to the electron CR in the GaNAs MQW, where a higher electron effective mass value and a much lower mobility are expected.
26.	Chen, Weimin, 1959-, et al. (författare) Role of the Substitutional Oxygen Donor in the Residual n-type Conductivity in GaN 1999 Konferensbidrag (refereegranskat)abstract A detailed photoluminescence (PL) study reveals a striking similarity in local vibrational properties of a defect center in GaN as compared to that for the substitutional OP donor in GaP. This observation could be interpreted as if the center is in fact related to the substitutional oxygen donor in GaN. The deep-level nature experimentally determined for the defect center calls for caution of a commonly referred model that the substitutional oxygen donor is responsible for the residual n-type conductivity in GaN.
27.	Choubina, Tatiana, 1950-, et al. (författare) Light diffusion in GaN epilayers 2007 Ingår i: 3rd International Conference on Spontaneous Coherence in Excitonic System,2007. Konferensbidrag (övrigt vetenskapligt/konstnärligt)
28.	Choubina, Tatiana, 1950-, et al. (författare) Realization of slow light in GaN crystals 2008 Ingår i: IWN 2008,2008. Konferensbidrag (refereegranskat)
29.	Choubina, Tatiana, 1950-, et al. (författare) Slow light in GaN 2008 Ingår i: 16th Int. Symp. ¿Nanostructures: Physics and Technology,2008. ; , s. 257- Konferensbidrag (refereegranskat)
30.	Choubina, Tatiana, 1950-, et al. (författare) The slow light in GaN 2008 Ingår i: ICPS2008,2008. ; , s. 647- Konferensbidrag (refereegranskat)
31.	Darakchieva, Vanya, 1971-, et al. (författare) Anisotropic strain and phonon deformation potentials in GaN 2007 Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:19, s. 195217- Tidskriftsartikel (refereegranskat)abstract We report optical phonon frequency studies in anisotropically strained c -plane- and a -plane-oriented GaN films by generalized infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The anisotropic strain in the films is obtained from high-resolution x-ray diffraction measurements. Experimental evidence for splitting of the GaN E1 (TO), E1 (LO), and E2 phonons under anisotropic strain in the basal plane is presented, and their phonon deformation potentials c E1 (TO), c E1 (LO), and c E2 are determined. A distinct correlation between anisotropic strain and the A1 (TO) and E1 (LO) frequencies of a -plane GaN films reveals the a A1 (TO), b A1 (TO), a E1 (LO), and b E1 (LO) phonon deformation potentials. The a A1 (TO) and b A1 (TO) are found to be in very good agreement with previous results from Raman experiments. Our a A1 (TO) and a E1 (LO) phonon deformation potentials agree well with recently reported theoretical estimations, while b A1 (TO) and b E1 (LO) are found to be significantly larger than the theoretical values. A discussion of the observed differences is presented. © 2007 The American Physical Society.
32.	Darakchieva, Vanya, 1971-, et al. (författare) Conduction band effective mass anisotropy and nonparabolicity of InN 2006 Ingår i: Proc. of 3rd Workshop on Indium Nitride. Konferensbidrag (refereegranskat)abstract Invited talk
33.	Darakchieva, Vanya, 1971-, et al. (författare) Deformation potentials of the E1 (TO) and E2 modes of InN 2004 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 84:18, s. 3636-3638 Tidskriftsartikel (refereegranskat)abstract The determination of deformation potentials of E1(TO) and E 2 modes of InN were discussed. The deformation potentials were evaluated for two sets of stiffness constants using x-ray diffraction, IR spectroscopic ellipsometry (IRSE), Raman scattering, and Grüneisen parameter values. The InN layer were grown on GaN buffer layers on (0001) sapphire by molecular beam epitaxy. It was found that the strain-free values of the InN E1(TO) mode was 477.9 cm-1 and 491.9 cm -1 for the E2 modes.
34.	Darakchieva, Vanya, 1971-, et al. (författare) Effects of strain and composition on the lattice parameters and applicability of Vegard's rule in Al-rich Al1-x Inx N films grown on sapphire 2008 Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 103:10, s. 103513- Tidskriftsartikel (refereegranskat)abstract The lattice parameters and strain evolution in Al1-x In x N films with 0.07≤x≤0.22 grown on GaN-buffered sapphire substrates by metal organic vapor phase epitaxy have been studied by reciprocal space mapping. Decoupling of compositional effects on the strain determination was accomplished by measuring the In contents in the films both by Rutherford backscattering spectrometry (RBS) and x-ray diffraction (XRD). Differences between XRD and RBS In contents are discussed in terms of compositions and biaxial strain in the films. It is suggested that strain plays an important role for the observed deviation from Vegard's rule in the case of pseudomorphic films. On the other hand, a good agreement between the In contents determined by XRD and RBS is found for Al1-x Inx N films with low degree of strain or partially relaxed, suggesting applicability of Vegard's rule in the narrow compositional range around the lattice matching to GaN. © 2008 American Institute of Physics.
35.	Darakchieva, Vanya, 1971-, et al. (författare) New insight into the free carrier properties of InN 2008 Ingår i: International workshop on Nitride semiconductors IWN2008,2008. Konferensbidrag (refereegranskat)abstract
36.	Darakchieva, Vanya, 1971-, et al. (författare) On the lattice parameters of GaN 2007 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:3, s. 031911- Tidskriftsartikel (refereegranskat)abstract The lattice parameters of low-defect density, undoped bulk GaN fabricated by hydride vapor phase epitaxy (HVPE) on (0001) sapphire and subsequent substrate removal, are precisely determined using high-resolution x-ray diffraction. The obtained values, c=5.18523 Å and a=3.18926 Å, are compared with the lattice parameters of freestanding HVPE GaN from different sources and found to be representative for state-of-the-art undoped HVPE bulk GaN material. A comparison with bulk GaN fabricated by the high-pressure technique and homoepitaxial GaN is made, and significant differences in the lattice parameters are found. The observed differences are discussed and a possible explanation is suggested. © 2007 American Institute of Physics.
37.	Darakchieva, Vanya, 1971-, et al. (författare) Phonon mode behavior in strained wurtzite AlN/GaN superlattices 2005 Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 71:11, s. 115329- Tidskriftsartikel (refereegranskat)abstract We have studied phonons in AlN/GaN superlattices with different periods but a constant well-to-barrier ratio using a combination of infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The strain evolution in the superlattice structures is assessed by high-resolution x-ray diffraction and reciprocal space mapping. We have identified E1(TO), A 1(LO) and E2 localized, and E1(LO) and A 1(TO) delocalized superlattice modes. The dependencies of their frequencies on in-plane strain are analyzed and discussed, and the strain-free frequencies of the superlattice modes are estimated. A good agreement between theory and experiment is found in the case of GaN localized modes, while large deviations between theoretically estimated and experimentally determined frequency shifts are observed for the AlN localized modes. The delocalization effect on the A1(TO) and E1(LO) phonons, as well as the free-carrier effect on the E1(LO) phonon are also discussed. ©2005 The American Physical Society.
38.	Darakchieva, Vanya, 1971-, et al. (författare) Phonons in strained AlGaN/GaN superlattices 2007 Ingår i: 6th International Symposium on Blue Laser and Light Emitting Diodes,2006. - Physica Status Solidi, vol C4 : WILEYVCH Verlag GmbH & Co. KGaA. ; , s. 170- Konferensbidrag (refereegranskat)
39.	Darakchieva, Vanya, 1971-, et al. (författare) Strain and compositional analyzes of Al-rich Al1-xInxN alloys grown by MOVPE : impact on the applicability of Vegard's rule 2008 Ingår i: Physica Status Solidi (C) Current Topics in Solid State Physics. - : Wiley. ; , s. 1859-1862 Konferensbidrag (refereegranskat)abstract We have studied composition and strain in Al1–xInxN films with 0.128≤ x≤ 0.22 grown on GaN-buffered sapphire substrates by metalorganic vapor phase epitaxy. A good agreement between the In contents determined by Rutherford backscattering spectrometry (RBS) and Xray diffraction (XRD) is found for x≤ 18, suggesting applicability of Vegard's rule in the narrow compositional range around the lattice matching to GaN. The increase of the In content up to x = 0.22 leads to a formation of sub-layers with a higher composition, accompanied by deviations from Vegard's rule. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
40.	Darakchieva, Vanya, 1971-, et al. (författare) Strain-related structural and vibrational properties of thin epitaxial AIN layers 2004 Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70:4, s. 045411- Tidskriftsartikel (refereegranskat)abstract The effect of film thickness on the strain and structural properties of thin epitaxial AIN films has been investigated by high resolution x-ray diffraction techniques and transmission electron microscopy. As a result a sublayer model of the degree of strain and related defects for all films is proposed. A sublayer with low defect density and a strain gradient is found to be present in all films and it reaches a maximum thickness of 65 nm. The films are compressively strained and the strain relaxation after a thickness of 65 nm is shown to be accompanied by misfit dislocation generation and increase of the mosaic tilt. The vibrational properties of the films have been studied by generalized infrared spectroscopic ellipsometry. The proposed sublayer model has been successfully applied to the analysis of the ellipsometry data through model calculations of the infrared dielectric function which confirm the sublayer model. It is found that the strain gradient results in a gradient of the phonon mode frequencies and broadening parameter. The initial strain relaxation in the films leads to narrowing of the observable infrared modes, while further strain relaxation broadens the modes when substantial defect generation occurs.
41.	Darakchieva, Vanya, 1971-, et al. (författare) Structural characteristics and lattice parameters of hydride vapor phase epitaxial GaN free-standing quasisubstrates 2005 Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 97:1, s. 013517- Tidskriftsartikel (refereegranskat)abstract We have studied the lattice parameters of hydride vapor phase epitaxy (HVPE)-GaN quasisubstrates in relation to their structural properties. Layers grown on single-layer metalorganic vapor phase epitaxy (MOVPE) templates and on epitaxial lateral overgrown MOVPE templates are characterized by Raman scattering, high-resolution x-ray diffraction, and reciprocal space mapping. The strain relaxation in the films versus their thickness was found to proceed similarly in the GaN samples grown using the two types of templates but the strain saturates at different nonzero levels. The lattice parameters of relatively thin HVPE-GaN free-standing quasisubstrates indicate that no total strain relaxation is achieved after the sapphire removal. The lattice parameters of the thick quasisubstrates grown on different templates are not affected by the separation process and are found to have values very close to the reference strain-free lattice parameters of GaN powder. © 2005 American Institute of Physics.
42.	Donchev, V., et al. (författare) Temperature Study of the Photoluminescence of a Single InAs/GaAs Quantum Dot 2004 Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - 1610-1634 .- 1610-1642. ; 3, s. 608- Tidskriftsartikel (refereegranskat)abstract Presented at: The 8th Conference on Optics of Excitons in Confined Systems, Lecce, Italy, February 3 - 4, 2003
43.	Esmaeili, M., et al. (författare) Photoluminescence study of MOCVD-grown GaN/AlGaN MQW nanostructures : Influence of Al composition and Si doping 2007 Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 18:2 Tidskriftsartikel (refereegranskat)abstract A detailed study of low-temperature photoluminescence (PL) in GaN/AlGaN multiple quantum well (MQW) nanostructures has been reported. We have investigated the effect of Si doping and Al content on PL spectra and PL decay time of these structures. The temperature dependence of radiative as well as non-radiative lifetimes have been evaluated between 2K and room temperature for different Si doping. We found that radiative recombination at higher temperatures even up to RT is stronger in the doped sample, compared to the undoped one. Hole localization in GaN/AlGaN MQWs with different compositions of Al is demonstrated via PL transient decay times and LO phonon coupling. It is found that there is an increasing of the decay time at the PL peak emission with increasing Al composition. For the undoped sample, a non-exponential PL decay behaviour at 2K is attributed to localized exciton recombination. A slight upshift in QWs PL peak with increasing Al composition is observed, which is counteracted by the expected rise of the internal QW electric field with increasing Al. The localization energies have been evaluated by studying the variation of the QW emission versus temperature and we found out that the localization energy increases with increasing Al composition. © IOP Publishing Ltd.
44.	Freitas, J., et al. (författare) Preface 2006 Ingår i: E-MRS 2006 Symposium S: Material Science and Technology of Wide Bandgap Semiconductors, 2006 Spring Meeting of the European Materials Research Society,2006. - Superlattices and Microstructures, Vol. 40 : Elsevier. ; , s. 191- Konferensbidrag (refereegranskat)abstract
45.	Gil, B., et al. (författare) Internal structure of the neutral donor-bound exciton complex in cubic zinc-blende and wurtzite semiconductors 2007 Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:8 Tidskriftsartikel (refereegranskat)abstract We calculate the fine structure splitting of the near band edge donor-bound excitons in major cubic semiconductors using an approach inspired by an earlier one that consists in replacing the Morse potential by a Kratzer one, in order to account for the repulsion between the donor and the hole. A regular trend is observed when plotting the computed results in terms of donor binding energies for all these semiconductors. Second, we extend the method to wurtzite semiconductors, namely CdS, GaN, and ZnO. The previously reported trend is found again, but enriched with the strong anisotropy of the dispersion relations in the valence band of these semiconductors. We end up in addressing a quantitative interpretation of the fine structure splitting of the donor bound exciton complex which includes the jj coupling between the valence band Bloch and the envelope nonrigid rotator hole states. © 2007 The American Physical Society.
46.	Godlewski, M., et al. (författare) Mechanism of radiative recombination in acceptor-doped bulk GaN crystals 1999 Ingår i: 20th International Conference on Defects in Semiconductors ICDS-20,1999. - Physica B, Vol. 273-274 : Elsevier. ; , s. 39- Konferensbidrag (refereegranskat)abstract Optical and electrical properties of acceptor-doped bulk GaN crystals are discussed. Though introducing Zn and Ca to bulk GaN does not significantly change electron concentration, it results in the appearance of a blue photoluminescence band accompanying the relatively strong yellow band usually present. Highly resistive GaN : Mg crystals are obtained when high amount of Mg is introduced to the Ga melt during high-pressure synthesis. Change of electrical properties of Mg-doped bulk crystals is accompanied by the appearance of a strong blue emission of GaN similar to that in Ca- and Zn-doped crystals. Optically detected magnetic resonance investigations indicate a multi-band character of this blue emission and suggest possible mechanism of compensation in acceptor-doped bulk GaN.
47.	Godlewski, M., et al. (författare) Photoluminescence mechanisms in undoped and in Mg doped bulk GaN 1999 Ingår i: 24th International Conference on the Physics of Semiconductors,1998. - Proc. of the 24th International Conference on the Physics of Semiconductors, ed. by D. Gershoni : World Scientific, Singapore. ; , s. IX B17- Konferensbidrag (övrigt vetenskapligt/konstnärligt)
48.	Gogova, Daniela, 1967-, et al. (författare) Epitaxial growth of β-Ga2O3 by hot-wall MOCVD 2022 Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 12:5 Tidskriftsartikel (refereegranskat)abstract The hot-wall metalorganic chemical vapor deposition (MOCVD) concept, previously shown to enable superior material quality and high performance devices based on wide bandgap semiconductors, such as Ga(Al)N and SiC, has been applied to the epitaxial growth of beta-Ga2O3. Epitaxial beta-Ga2O3 layers at high growth rates (above 1 mu m/h), at low reagent flows, and at reduced growth temperatures (740 degrees C) are demonstrated. A high crystalline quality epitaxial material on a c-plane sapphire substrate is attained as corroborated by a combination of x-ray diffraction, high-resolution scanning transmission electron microscopy, and spectroscopic ellipsometry measurements. The hot-wall MOCVD process is transferred to homoepitaxy, and single-crystalline homoepitaxial beta-Ga2O3 layers are demonstrated with a 201 rocking curve width of 118 arc sec, which is comparable to those of the edge-defined film-fed grown (201) beta-Ga2O3 substrates, indicative of similar dislocation densities for epilayers and substrates. Hence, hot-wall MOCVD is proposed as a prospective growth method to be further explored for the fabrication of beta-Ga2O3.
49.	Gogova, D., et al. (författare) Investigation of the structural and optical properties of free-standing GaN grown by HVPE 2005 Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 38:14, s. 2332-2337 Tidskriftsartikel (refereegranskat)abstract The potential of the high-growth rate hydride vapour phase epitaxy technique and laser lift-off for the fabrication of free-standing GaN substrates is explored. Structural and optical properties of 300 νm thick free-standing GaN have been investigated employing different analytical techniques. The x-ray diffraction (XRD) measurements prove good crystalline quality of the material grown. A comparatively low value of (3 ± 1) × 1016 cm-3 of Ga vacancy-related defects is inferred from positron annihilation spectroscopy data. Complete strain relaxation is observed on the Ga-polar face of the free-standing GaN by XRD and Raman spectroscopy measurements. The strain-free homoepitaxy will significantly reduce the defect density, and thus an improvement of the device performance and lifetime can be realized. © 2005 IOP Publishing Ltd.
50.	Gogova, Daniela, 1967-, et al. (författare) Strain-free bulk-like GaN grown by hydride-vapor-phase-epitaxy on two-step epitaxial lateral overgrown GaN template 2004 Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 96:1, s. 799-806 Tidskriftsartikel (refereegranskat)abstract Crack-free bulk-like GaN with high crystalline quality has been obtained by hydride-vapor-phase-epitaxy (HVPE) growth on a two-step epitaxial lateral overgrown GaN template on sapphire. During the cooling down stage, the as-grown 270-μm-thick GaN layer was self-separated from the sapphire substrate. Plan-view transmission electron microscopy images show the dislocation density of the free-standing HVPE-GaN to be ∼2.5×107 cm−2 on the Ga-polar face. A low Ga vacancy related defect concentration of about 8×1015 cm−3 is extracted from positron annihilation spectroscopy data. The residual stress and the crystalline quality of the material are studied by two complementary techniques. Low-temperature photoluminescence spectra show the main neutral donor bound exciton line to be composed of a doublet structure at 3.4715 (3.4712) eV and 3.4721 (3.4718) eV for the Ga- (N-) polar face with the higher-energy component dominating. These line positions suggest virtually strain-free material on both surfaces with high crystalline quality as indicated by the small full width at half maximum values of the donor bound exciton lines. The E1(TO) phonon mode position measured at 558.52 cm−1 (Ga face) by infrared spectroscopic ellipsometry confirms the small residual stress in the material, which is hence well suited to act as a lattice-constant and thermal-expansion-coefficient matched substrate for further homoepitaxy, as needed for high-quality III-nitride device applications. © 2004 American Institute of Physics.

Skapa referenser, mejla, bekava och länka

Länka till träfflistan

Träfflista för sökning "WFRF:(Monemar Bo 1942 ) "

Avgränsa träffmängd

År