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Jin Seo Im

Bio: Jin Seo Im is an academic researcher from University of Stuttgart. The author has contributed to research in topics: Quantum well & Photoluminescence. The author has an hindex of 13, co-authored 19 publications receiving 1148 citations. Previous affiliations of Jin Seo Im include Braunschweig University of Technology.

Papers
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TL;DR: In this paper, the authors demonstrate a dramatic reduction of the oscillator strength in quantum wells due to piezoelectric fields, showing a strong increase of the luminescence decay time of the dominating transition with increasing well width in parallel to a redshift of the emission peaks.
Abstract: We demonstrate a dramatic reduction of the oscillator strength in ${\mathrm{G}\mathrm{a}\mathrm{N}/\mathrm{A}\mathrm{l}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ quantum wells due to piezoelectric fields. Our study using time-resolved photoluminescence spectroscopy reveals a strong increase of the luminescence decay time of the dominating transition with increasing well width by several orders of magnitude in parallel to a redshift of the emission peaks. The experimental results are consistently explained by a quantitative model based on the piezoelectric fields in strained wurtzite quantum wells. We estimate the piezoelectric constant of GaN to ${d}_{31}=\ensuremath{-}0.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ cm/V.

568 citations

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TL;DR: In this paper, the lifetime of excess charge carriers in GaN epitaxial layers grown on sapphire at temperatures up to 300 K was measured by using picosecond time-resolved photoluminescence.
Abstract: By using picosecond time-resolved photoluminescence we have measured the lifetime of excess charge carriers in GaN epitaxial layers grown on sapphire at temperatures up to 300 K. The decay time turns out to be dominated by trapping processes at low excitation levels. The radiative lifetime derived from our data is dominated by free excitons at temperatures below 150 K, but also clearly shows the gradual thermal dissociation of excitons at higher temperatures. From our data, we are able to determine the free exciton binding energy and the free carrier radiative recombination coefficient. By combining these data with optical absorption data, we find the interband momentum matrix element and an estimate for the hole effective mass, which is much larger than previously thought.

197 citations

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TL;DR: In this article, the authors focus on the consequences of the piezoelectric field, which is an inherent consequence of the commonly used wurtzite phase of GaN, on the optical properties of strained GaN-based quantum well structures.
Abstract: In this contribution, we focus on the consequences of the piezoelectric field, which is an inherent consequence of the commonly used wurtzite phase of GaN, on the optical properties of strained GaN-based quantum well structures. We demonstrate that both in GaN/AlGaN and in GaInN/GaN single quantum well structures, the piezoelectric field leads to a Stark-shift of the fundamental optical transitions, which can lead to luminescence emission far below the bulk bandgap. Due to the spatial separation of the electron and hole wavefunctions in such structures, the oscillator strength of these transitions may become extremely small, many orders of magnitude lower than in the field-free case. From specially designed structures, we can even determine the sign of the piezoelectric field and relate it to the polarity of the layers. Under high-excitation conditions, as found in a laser diode, the piezoelectric field is almost completely screened by the injected carriers. As a consequence, the stimulated emission is significantly blue-shifted compared to the photoluminescence, which has sometimes been confused with localization effects.

135 citations

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TL;DR: In this article, the authors studied optical transitions in GaInN/GaN single and multiple quantum wells using time-resolved photoluminescence spectroscopy and showed that the energy positions of the dominant emission lines strongly depend both on the well width and on the number of wells.
Abstract: We have studied optical transitions in GaInN/GaN single and multiple quantum wells using time-resolved photoluminescence spectroscopy. Our results show that the energy positions of the dominant emission lines strongly depend both on the well width and on the number of wells. In the case of multiple quantum wells, time-resolved measurements clearly distinguish multiple emission lines. These observations are consistently explained by considering the large built-in piezoelectric field in strained GaInN quantum wells. The multiple emission lines are attributed to intra- and interwell transitions between nearest and next-nearest neighbors.

59 citations

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TL;DR: In this paper, the authors show that the large linewidth of optical transitions and the sizeable Stokes shift in nitride quantum wells can be easily understood in terms of the huge piezoelectric fields present in such structures.
Abstract: Both the large linewidth of optical transitions as well as the sizeable “Stokes” shift seem to suggest strong localization effects in nitride quantum wells. In contrast, we clearly show that the “Stokes” shift can be easily understood in terms of the huge piezoelectric fields present in such structures. At the same time, those fields lead to a characteristic dependence of the linewidth on well width, which we use to quantitatively separate fluctuation and field effects. We find that in high-quality quantum wells, the relative compositional fluctuation is less than 10% and the well width fluctuation is of the order 1 monolayer.

40 citations


Cited by
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TL;DR: In this article, the authors present a comprehensive, up-to-date compilation of band parameters for the technologically important III-V zinc blende and wurtzite compound semiconductors.
Abstract: We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

6,349 citations

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TL;DR: In this article, the authors investigated the role of spontaneous and piezoelectric polarization on the carrier confinement at GaN/AlGaN and AlGaN/GaN interfaces.
Abstract: Carrier concentration profiles of two-dimensional electron gases are investigated in wurtzite, Ga-face AlxGa1−xN/GaN/AlxGa1−xN and N-face GaN/AlxGa1−xN/GaN heterostructures used for the fabrication of field effect transistors. Analysis of the measured electron distributions in heterostructures with AlGaN barrier layers of different Al concentrations (0.15

2,581 citations

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TL;DR: In this paper, a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III-V semiconductors that have been investigated to date is presented.
Abstract: We present a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III–V semiconductors that have been investigated to date. The two main classes are: (1) “conventional” nitrides (wurtzite and zinc-blende GaN, InN, and AlN, along with their alloys) and (2) “dilute” nitrides (zinc-blende ternaries and quaternaries in which a relatively small fraction of N is added to a host III–V material, e.g., GaAsN and GaInAsN). As in our more general review of III–V semiconductor band parameters [I. Vurgaftman et al., J. Appl. Phys. 89, 5815 (2001)], complete and consistent parameter sets are recommended on the basis of a thorough and critical review of the existing literature. We tabulate the direct and indirect energy gaps, spin-orbit and crystal-field splittings, alloy bowing parameters, electron and hole effective masses, deformation potentials, elastic constants, piezoelectric and spontaneous polarization coefficients, as well as heterostructure band offsets. Temperature an...

2,525 citations

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TL;DR: The role of extended and point defects, and key impurities such as C, O, and H, on the electrical and optical properties of GaN is reviewed in this article, along with the influence of process-induced or grown-in defects and impurities on the device physics.
Abstract: The role of extended and point defects, and key impurities such as C, O, and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation, and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes, and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

1,693 citations

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TL;DR: In this article, the chemical and thermal stability of epitaxial nitride films is discussed in relation to the problems of deposition processes and the advantages for applications in high-power and high-temperature devices.
Abstract: Recent research results pertaining to InN, GaN and AlN are reviewed, focusing on the different growth techniques of Group III-nitride crystals and epitaxial films, heterostructures and devices. The chemical and thermal stability of epitaxial nitride films is discussed in relation to the problems of deposition processes and the advantages for applications in high-power and high-temperature devices. The development of growth methods like metalorganic chemical vapour deposition and plasma-induced molecular beam epitaxy has resulted in remarkable improvements in the structural, optical and electrical properties. New developments in precursor chemistry, plasma-based nitrogen sources, substrates, the growth of nucleation layers and selective growth are covered. Deposition conditions and methods used to grow alloys for optical bandgap and lattice engineering are introduced. The review is concluded with a description of recent Group III-nitride semiconductor devices such as bright blue and white light-emitting diodes, the first blue-emitting laser, high-power transistors, and a discussion of further applications in surface acoustic wave devices and sensors.

1,386 citations