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  • 1
    Digitale Medien
    Digitale Medien
    Optical properties of wurtzite GaN grown by low-pressure metalorganic chemical-vapor deposition (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3691-3696 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present the results of optical studies on the properties of GaN grown by low-pressure metalorganic chemical-vapor deposition, with emphasis on the issues vital to device applications such as stimulated emission and laser action as well as carrier relaxation dynamics. By optical pumping, stimulated emission and lasing were investigated over a wide temperature range up to 420 K. Using a picosecond streak camera, the free and bound exciton emission decay times were examined. In addition, the effects of temperature and pressure on the optical interband transitions and the transitions associated with impurity/defect states were studied using a variety of spectroscopic methods, including photoluminescence and photoreflectance. The fundamental band gap of GaN was mapped out as a function of temperature using the empirical Varshni relation. The pressure coefficient of the gap was determined using diamond-anvil pressure-cell technique. The hydrostatic deformation potential for the direct Γ band gap was also derived from the experimental results. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.361200
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  • 2
    Digitale Medien
    Digitale Medien
    Femtosecond fluorescence depletion spectroscopy of NO2 multiphoton dissociation dynamics (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 7183-7186 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Two-color femtosecond pump–probe spectroscopy has been applied to the multiphoton dissociation of NO2 with a time resolution of ≤350 fs. At laser intensities in the range (similar, equals)3×1012–2×1013 W cm−2 and a wavelength of 400 nm, NO2 absorbs three photons before dissociation. Nascent NO A 2Σ+ product in its n′=0 and 1 vibrational levels is probed by single-photon fluorescence depletion at 800 nm. Analyses of the ultrafast transient behavior at different intensities leads to an estimate of ≤600 fs for formation of NO A 2Σ+ n′=0 and 1. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.480046
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  • 3
    Digitale Medien
    Digitale Medien
    Diffraction of high-energy synchrotron radiation (invited) (abstract) : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1614-1614 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Diffraction of high-energy synchrotron radiation at energies above 100 keV combines advantages of conventional x-ray diffraction and neutron diffraction. For hard x rays absorption in matter is weak with typical mean free paths of several millimeters. Bulk properties are studied on large samples. With a three-crystal diffractometer an excellent k-space resolution of about 10−5 A(ring)−1 transversal and 10−4 A(ring)−1 longitudinal is achieved. In this contribution the particularities of hard x rays, the instrumental setup, and the k-space resolution are discussed and presented. The potential of the new method will be demonstrated on two examples: magnetic diffraction from MnF2 and the structural phase transition of SrTiO3. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1146465
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  • 4
    Digitale Medien
    Digitale Medien
    Ag-induced multistep formation on Si(001) (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2185-2187 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The step topography of 4°-misoriented Si(001) surfaces was examined by scanning tunneling microscopy and spot profile analyzing–low-energy electron diffraction. The clean Si(001)-(2×1) surface proves to be a single domain substrate, which is characterized by a regular array of double steps. This step structure is changed dramatically upon adsorption of submonolayer quantities of Ag at ∼700 K. In this case, the formation of multisteps with fourfold, sixfold, and eightfold step heights occurs. The single domain character of the substrate is preserved, now showing a Ag-induced (3×2) reconstruction. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.115097
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  • 5
    Digitale Medien
    Digitale Medien
    Energy selective optically pumped stimulated emission from InGaN/GaN multiple quantum wells (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 560-562 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Optically pumped stimulated emission (SE) from InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition has been systematically studied as a function of excitation photon energy (Eexc) to further understand the origin of SE in these structures. Optically pumped SE was observed for excitation photon energies well below that of the absorption edge of the MQWs, indicating the states responsible for the soft absorption edge in these structures can efficiently couple carriers with the gain region. "Mobility edge"-type behavior in the SE peak was observed as Eexc was varied. The effective mobility edge measured in these SE experiments lies ∼110 meV above the main spontaneous emission peak and ∼62 meV above the SE peak. Tuning the excitation energy below the mobility edge was found to be accompanied by a drastic increase in the SE threshold due to a decrease in the effective absorption cross section. The experimental results indicate that the SE peak observed here has the same microscopic origin as the spontaneous emission peak, i.e., radiative recombination of localized states. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.121855
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  • 6
    Digitale Medien
    Digitale Medien
    Stimulated emission characteristics of InGaN/GaN multiple quantum wells: Excitation length and excitation density dependence (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3689-3691 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Optically pumped stimulated emission (SE) from InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition has been systematically studied as a function of excitation length (Lexc). Two distinct SE peaks were observed from these structures: one that originates at 425 nm at 10 K (430 nm at 300 K) and another that originates at 434 nm at 10 K (438 nm at 300 K). The SE threshold for the high-energy peak was observed to always be lower than that of the low-energy peak, but the difference was found to decrease greatly with increasing Lexc. A detailed study of the emission intensity of these two SE peaks as a function of excitation density shows that the two peaks compete for gain in the MQW active region. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.122864
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  • 7
    Digitale Medien
    Digitale Medien
    Single-electron effects in slim semiconductor superlattices (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1982-1984 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We fabricated laterally confined GaAs–AlGaAs superlattices with diameters between 500 nm and 2 μm. With decreasing device diameter, a gap evolves in the current–voltage curve around zero bias and steps show up at the onset of the current. This behavior is interpreted in terms of Coulomb blockade, a depletion of the center of the superlattice, and single-electron tunneling through donor levels. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.122342
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  • 8
    Digitale Medien
    Digitale Medien
    High-temperature stimulated emission in optically pumped InGaN/GaN multiquantum wells (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 1623-1625 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Stimulated emission (SE) in optically pumped InGaN/GaN multiquantum well (MQW) structures grown by metalorganic chemical vapor deposition was experimentally studied in the temperature range of 175–575 K. The GaN barriers were intentionally doped with a different Si concentration ranging from 1×1017 to 3×1019 cm−3 and the effects of Si doping of GaN barriers on the optical properties of InGaN/GaN MQWs were investigated. The SE threshold was measured as a function of temperature and compared with bulk GaN. We observed that the SE threshold had a low value and a weak temperature dependence: for example, ∼25 kW/cm2 at 175 K, ∼55 kW/cm2 at 300 K, and ∼300 kW/cm2 at 575 K for one of the samples. Low SE thresholds are attributed to the high-quantum efficiency of the MQWs, possibly associated with the large localization of excitons. The characteristic temperature of 162 K was derived from the temperature dependence of the SE threshold. The integrated emission intensity versus pumping density was examined for different temperatures. This study shows that InGaN/GaN MQWs are suitable for development of laser diodes that can operate well above room temperature. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.121133
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  • 9
    Digitale Medien
    Digitale Medien
    Near-threshold gain mechanisms in GaN thin films in the temperature range of 20–700 K (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1-3 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report the results of an experimental study on near-threshold gain mechanisms in optically pumped GaN epilayers in the temperature range of 20–700 K. High-quality single-crystal GaN films grown on 6H–SiC and (0001) sapphire were used in this study. We show that the dominant near-threshold gain mechanism is inelastic exciton–exciton scattering for temperatures below ∼150 K, characterized by band-filling phenomena and a low stimulated emission (SE) threshold. An analysis of both the temperature dependence of the SE threshold and the relative shift between stimulated and band-edge-related emission indicates electron–hole plasma is the dominant gain mechanism for temperatures exceeding 150 K. Based on our results, we discuss possibilities of reducing the room-temperature lasing threshold in laser diode structures with a GaN active medium. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.123114
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  • 10
    Digitale Medien
    Digitale Medien
    Bi: Perfect surfactant for Ge growth on Si(111)? (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1391-1393 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have investigated the growth of Ge on Bi-terminated Bi:Si(111)-(square root of 3)×(square root of 3). In-situ measurements of x-ray standing waves, crystal truncation rods and scanning tunneling microscopy clearly show that, at substrate temperatures around 485 °C, smooth and homogeneous Ge films of thicknesses exceeding 30 bilayers Ge can be grown. For Ge coverages larger than 10 bilayers, the Ge film is completely relaxed. Bi is found to segregate to the surface during Ge deposition, and can be removed from the surface after growth by mild annealing at 520 °C as proven by Auger electron spectroscopy. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.123560
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