Showing papers by "Jean Massies published in 2002"
TL;DR: In this paper, the size dependence of the coupling between electron-hole pairs and longitudinal-optical phonons in Ga1−xInxN/GaN-based quantum wells and quantum boxes was studied.
Abstract: We present an experimental and theoretical study of the size dependence of the coupling between electron–hole pairs and longitudinal-optical phonons in Ga1−xInxN/GaN-based quantum wells and quantum boxes. We found that the Huang–Rhys factor S, which determines the distribution of luminescence intensities between the phonon replicas and the zero-phonon peak, increases significantly when the vertical size of the boxes or the thickness of quantum well increases. We assign this variation to (1) the strong electric field present along the growth axis of the system, due to spontaneous and piezoelectric polarizations in these wurtzite materials, and (2) the localization on separate sites of electrons and holes in the plane of the wells or boxes, due to potential fluctuations in the ternary alloy. Indeed, envelope-function calculations for free or localized excitons, with electron–hole distance only controlled by Coulomb interaction, do not account quantitatively for the measured behavior of the S factor. In fact...
67 citations
TL;DR: In this article, it was shown that the luminance intensity varies quadratically with the injection current, showing that the electroluminescence originates from the depleted region of the diode, and that non-radiative recombination paths exist.
Abstract: Multicolor, multi-quantum well light emitting diodes have been fabricated by molecular beam epitaxy by inserting quantum wells of various widths in the active region. The In content of the wells is 15%-20% and the color is governed by carrier confinement and the Stark effect. Combining a proper number of blue and yellow quantum wells allows to obtain monolithic white LEDs. The electroluminescence spectra of the diodes have been studied. At low injection, the luminescence intensity varies quadratically with the injection current, showing that the electroluminescence originates from the depleted region of the diode, and that non-radiative recombination paths exist. However, for higher injection currents, the luminescence efficiency of the wells situated near the n-side of the junction starts to vary linearly with the current, and this is accompanied by the appearance of GaN electroluminescence. We show that this is due to the entering of these wells into the neutral region of the diode, explaining the injection dependence of the color of these multicolor LEDs.
55 citations
TL;DR: The optical properties of Al x Ga 1-x N samples (x < 0.7) have been studied by photoluminescence (PL) and reflectivity in the 10-300 K temperature range.
Abstract: The optical properties of Al x Ga 1-x N samples (x < 0.7) have been studied by photoluminescence (PL) and reflectivity in the 10-300 K temperature range. Various physical properties have been studied as a function of composition, such as Stokes shift, alloy broadening, exciton localization, and Huang-Rhys factor. Up to x 0.3, a band gap bowing factor of ∼0.9 eV accounts for the variation of PL and reflectivity energies. At higher compositions, luminescence energies deepen with regard to this behaviour. This is interpreted as a consequence of the Γ 9 -Γ 7 crossover of the valence band maxima. This is confirmed by the linear polarization of the luminescence studied under oblique observation.
45 citations
TL;DR: In this article, a solar blind metal-semiconductor-metal detectors have been fabricated based on AlGaN grown on Si by molecular-beam epitaxy, and submicron finger spacings were obtained by electron-beam lithography, and demonstrated a significant improvement of the responsivity and spectral selectivity.
Abstract: Solar blind metal–semiconductor–metal detectors have been fabricated based on AlGaN grown on Si by molecular-beam epitaxy. Submicron finger spacings were obtained by electron-beam lithography, and allowed us to demonstrate a significant improvement of the responsivity and the spectral selectivity. These results were explained by numerical two-dimensional calculations of the electric-field distribution. The simulation also explained the dependence of the response on applied bias.
39 citations
TL;DR: In this article, a high electron mobility transistor (HEMT) with 0.5 µm gate length and a maximum extrinsic transconductance of 160 µmS/mm and drain-source current exceeding 600 µmA/mm is presented.
Abstract: Al0.3Ga0.7N/GaN high electron mobility transistor (HEMT) structures have been grown on resistive Si(111) substrate by molecular beam epitaxy (MBE) using ammonia (NH3). The use of an AlN/GaN intermediate layer allows a resistive buffer layer to be obtained. High sheet carrier density and high electron mobility are obtained in the channel. A device with 0.5 μm gate length has been realised exhibiting a maximum extrinsic transconductance of 160 mS/mm and drain-source current exceeding 600 mA/mm. Small-signal measurements show ft of 17 GHz and fmax of 40 GHz.
24 citations
TL;DR: In this paper, the authors used a mixture of AlN and AlGaN reflectors for the UV spectral region and obtained high reflectance values, for a relatively rather small number of periods (15), because of the larger refractive index ratio between AlNs and GaN compared to traditional AlGaNs/GaN DBRs.
Abstract: Quarter-wave distributed Bragg reflectors (DBRs) consisting of AlN and AlxGa1-xN (x=0.25±3%) stacked layers designed for the UV spectral region have been grown on silicon substrates by molecular beam epitaxy. Transmission electron microscopy, Rutherford Back-Scattering and photoluminescence have been performed to assess the structural quality and the composition of DBRs. High reflectance values (91%) are obtained, for a relatively rather small number of periods (15), because of the larger refractive index ratio between AlN and AlGaN compared to traditional AlGaN/GaN DBRs. The experimental reflectance data were compared with calculations and show excellent agreement with respect to peak reflectance and spectral width.
21 citations
Journal Article•
TL;DR: In this paper, the authors used a mixture of AlN and AlGaN reflectors for the UV spectral region and obtained high reflectance values, for a relatively rather small number of periods (15), because of the larger refractive index ratio between AlNs and GaN compared to traditional AlGaNs/GaN DBRs.
Abstract: Quarter-wave distributed Bragg reflectors (DBRs) consisting of AlN and AlxGa1-xN (x=0.25±3%) stacked layers designed for the UV spectral region have been grown on silicon substrates by molecular beam epitaxy. Transmission electron microscopy, Rutherford Back-Scattering and photoluminescence have been performed to assess the structural quality and the composition of DBRs. High reflectance values (91%) are obtained, for a relatively rather small number of periods (15), because of the larger refractive index ratio between AlN and AlGaN compared to traditional AlGaN/GaN DBRs. The experimental reflectance data were compared with calculations and show excellent agreement with respect to peak reflectance and spectral width.
19 citations
TL;DR: In this paper, the size dependence of the coupling between optical phonons and electron-hole pairs in InxGa1-xN/GaN quantum wells and quantum boxes has been investigated.
Abstract: The size dependence of the coupling between longitudinal optical phonons and electron-hole pairs in InxGa1-xN/GaN quantum wells and quantum boxes has been investigated. The distribution of luminescence intensities between the phonon replicas and the zero-phonon peak is found to depend significantly on the well width or the vertical size of the boxes. The Huang-Rhys factor, S, which describes the strength of the coupling between LO-phonons and electron-hole pairs, increases steadily with the vertical size. This behavior is assigned to 1. the spontaneous and piezoelectric polarization-induced strong electric field along the growth axis of the system and 2. to the localization of electrons and holes at opposite sides of the well (or box) resulting from potential fluctuations in the ternary alloy. This conclusion is reinforced by envelope function calculations of S, for free or localized excitons, where only the Coulomb interaction is responsible for the electron-hole distance. This model does not give any quantitative agreement with the experimental results which are rather similar to what is obtained for donor-acceptor pairs, with separate centers of localization for electrons and for holes.
18 citations
TL;DR: In this article, a process to fabricate AlGaN/GaN HEMTs based on [111] silicon substrate was developed, and the device structure was grown on a resistive [111]- silicon substrate.
Abstract: A process to fabricate AlGaN/GaN HEMTs based on [111] silicon substrate is developed. The device structure is grown on a resistive [111] silicon substrate. The frequency F/sub t/ is 28 GHz and the frequency F/sub max/ is 50 GHz. At 4 GHz, the power density is 1 W/mm for a 150 /spl times/ 1 /spl mu/m/sup 2/ device.
16 citations
TL;DR: In this article, the absorption coefficient of the InGaN/GaN multi-quantum well (MQW) structures grown by molecular beam epitaxy on (0001) sapphire substrates was extracted by modelling the TDOA lineshape.
Abstract: Thermally detected optical absorption (TDOA) and photoluminescence experiments were carried out on InGaN/GaN multi-quantum well (MQW) structures grown by molecular beam epitaxy on (0001) sapphire substrates. The absorption coefficient of the QW was extracted by modelling the TDOA lineshape. These experimental findings are confronted with the theoretical optical density evaluated within envelope function calculations of transition energies and oscillator strengths, including the electric field effects. The results show a relative agreement obtained by using a smaller value of the electric field than it has been predicted theoretically. However, other effects must be included in our model in order to achieve a realistic description of the absorption process in this sophisticated system.
14 citations
TL;DR: In this paper, the authors performed a study of excitation power-dependent spectra of GaN/AlGaN single quantum wells (QWs) and found that the experimental "blueshift" of the emission energy, due to screening of internal piezoelectric fields, was compared with the model calculations based on self-consistent solution of Schroedinger and Poisson equations.
Abstract: We have performed a study of excitation power-dependent spectra of GaN/AlGaN single quantum wells (QWs). First, the experimental "blueshift" of the emission energy, due to screening of internal piezoelectric fields, was compared with the model calculations based on self-consistent solution of Schroedinger and Poisson equations. We found that, even for the highest applied levels of excitation power (2.5 MW/cm(2)), only 0.5x10(12) cm(-2) carriers were present in the QW layers. Second, we analyzed the evolution of power-dependent spectra of two single QW having different widths. For the thinner QW (2.1 nm), the peak corresponding to a QW photoluminescence (PL) emission dominates the entire spectrum in the whole range of the used excitation power. In the case of the wider QW (4.4 nm), for sufficiently high excitation power, we observe the effect of PL quenching. Using the rate equation model we show that the observed effect of the PL quenching can be associated with the reduction of exciton binding energy due to the many body interactions in the QW. (C) 2002 American Institute of Physics.
TL;DR: In this paper, the indium surface segregation is evidenced in real time by reflection high-energy electron diffraction (RHEED) during the molecular beam epitaxial growth of AlSb on InAs(Sb).
Abstract: Indium surface segregation is evidenced in real time by reflection high-energy electron diffraction (RHEED) during the molecular beam epitaxial growth of AlSb on InAs(Sb). The resulting interface width is determined from the RHEED specular beam intensity variation during the growth. It extends over several nanometers and increases with the growth temperature. Band structure simulations show that the indium segregation leads to a strong localization of the wave function associated to the first bound hole level at the AlSb on InAs(Sb) interface.
TL;DR: In this article, the influence of the number of stacked layers and the different electron beam injection conditions on the main optical emissions was studied by means of cathodoluminescence, revealing transitions from 2.5 and 4.4 eV.
Abstract: GaN/AlN-based heterostructures made from stacked GaN quantum dots (QDs) have been studied by means of the cathodoluminescence (CL), photoluminescence (PL), near-field scanning optical microscopy (NSOM) and micro-Raman techniques. The influence of the number of stacked layers (2–85) and of the different electron beam injection conditions on the main optical emissions was studied by means of CL, revealing transitions from 2.5 and 4.4 eV. Power-dependent cross-sectional CL studies revealed a large (87–180 meV) blue-shift only for the optical bands located in the 2.5 and 3.1 eV spectral range. This observation enabled us to assign a zero-dimensional character to those bands. The results were confirmed by PL and NSOM studies. Different values of the blue-shift were found for specimens with different numbers of stacked layers. This suggested the presence of different residual strains inside the structures, as confirmed by micro-Raman studies. An inhomogeneous distribution of the QD emissions was also observed both in the plane and along the growth direction.
TL;DR: In this article, a detailed investigation of the exciton and free-carrier dynamics in high quality GaN/AlGaN MBE-grown quantum wells under different experimental conditions is presented.
Abstract: We present a detailed investigation of the exciton and free-carrier dynamics in high quality GaN/ AlGaN MBE-grown quantum wells under different experimental conditions. In particular time-resolved photoluminescence spectra clearly indicate a major role played by the photoinduced screening of the internal electric field in the carrier recombination. Resonant and non-resonant time-resolved spectra are compared, suggesting a more efficient screening of the field when the carriers are created in the well. Experimental data are analyzed in the framework of a model based on the self-consistent solution of both Schrodinger and Poisson equations and a rate-equation for the time evolution of the carrier dynamics.
TL;DR: In this article, the ion beam induced charge collection method was used for metal-semiconductor-metal detectors and the results were explained by numerical two-dimensional calculations of the electric field distribution.
Abstract: Metal–semiconductor–metal detectors have been fabricated based on AlGaN grown on Si by molecular beam epitaxy. Field distribution and collection efficiency were studied with the ion beam induced charge collection method. The results were explained by numerical two-dimensional calculations of the electric field distribution. The calculated field map and charge buildup at the electrodes are used to explain the bias and position dependence of the ion beam induced charge collection. The similarities and differences with the case of optical detection are discussed.
TL;DR: In this paper, a steady-state and time-resolved near-field scanning optical spectroscopy on GaN/AlN quantum dot (QD) structures and InGaN/GaN multiple quantum wells (MQWs) was performed.
Abstract: In this paper we performed steady-state and time-resolved near-field scanning optical spectroscopy on GaN/AlN quantum dot (QD) structures and InGaN/GaN multiple quantum wells (MQWs). The morphology of the QD sample is composed of islands in the 500-1000 nm range on the top of which dots nucleate. These islands are separated by slightly smaller structures showing less intense luminescence. Time-resolved photoluminescence mapping (spatially and spectrally resolved) of InGaN/GaN MQW structures revealed bright and dark spots with nearly constant peak energy and time decay. The results suggest that the bright and dark spots of the samples correspond to islands with higher and lower absolute number of QD-like regions where the excitons are localized.
10 Dec 2002
TL;DR: In this paper, the structural quality of the epilayers as well as electrical properties have been investigated in a reactive molecular beam epitaxy system using ammonia (Riber Compact 21).
Abstract: For high-power and high-frequency electronic applications, the III-V nitride layers are usually grown on sapphire or silicon carbide substrates. However, the development of these applications on silicon substrates has obvious technological advantages (cost, integration). In the present work, AlGaN/GaN heterostructures are grown on a resistive [111] silicon substrate (4000-10000 /spl Omega/.cm) in a reactive molecular beam epitaxy system using ammonia (Riber Compact 21). The structural quality of the epilayers as well as electrical properties have been investigated. AlGaN/GaN HEMT devices with different gate lengths and source to drain spacings have been realized in order to investigate their static characteristics and RF power performances.
TL;DR: Magnetophotoluminescence has been studied from a single undoped GaN/AlxGa1-xN heterojunction with a linewidth of 25 meV as discussed by the authors.
Abstract: Magnetophotoluminescence has been studied from a single undoped GaN/AlxGa1-xN heterojunction with a linewidth of 25 meV The peak originates from the recombination of a photoexcited hole with an electron in the two-dimensional electron gas (2DEG) formed as a result of spontaneous and piezoelectric polarizations at the interface The photoluminescence intensity is strongly enhanced at filling factors corresponding to filled Landau levels as a result of the reduced screening of the Coulomb interaction by the 2DEG This prevents the rapid diffusion of photoexcited holes away from the heterojunction The energy of the magnetoexcitonic recombination indicates a very low value for the hole mass of 03m(0) close to the band edge in agreement with theory
TL;DR: In this article, two GaN microcavities have been grown on Si(111) substrates by molecular beam epitaxy, and reflectivity and photoluminescence experiments were carried out under normal incidence at low temperature (T = 5 K).
Abstract: Two GaN microcavities have been grown on Si(111) substrates by molecular beam epitaxy. The first one is constituted of a (λ/2) GaN cavity with 12 (λ/4) AlN/Al 0.20 Ga 0.80 N bilayers as the top mirror, the Si substrate acting as the bottom mirror. The second one is a (2λ) GaN cavity sandwiched between 13 and 15 AlN/Al 0.20 Ga 0.80 N periods, respectively, for the top and bottom mirrors. Reflectivity and photoluminescence experiments were carried out under normal incidence at low temperature (T = 5 K). The reflectivity spectra reveal a cavity mode whose linewidth is about 30 meV. Our experiments demonstrate that the cavity mode controls the GaN emission. The modelling of the luminescence spectra as a function of the cavity resonance energy allows to estimate the spectral broadening of the GaN emission line to about 50 meV; this value seems to be responsible for the non-observation of the strong coupling.
TL;DR: In this article, the In K-edge EXAFS spectrum of an ultrathin, uncapped 'quantum box' (QB) sample is compared to results obtained previously on thick luminescent InGaN epilayers with a range of composition.
Abstract: Extended X-ray absorption fine structure (EXAFS) above the In K-edge of luminescent InGaN heterostructures provides a unique probe of local structure on an atomic length scale. Through a process of fitting the experimental spectrum, we can refine a model of the probable configuration (the atom type, co-ordination number and radial separation) of the first few shells of neighbouring atoms in the vicinity of a selected probe atom. We present here, for the first time, the In K-edge EXAFS spectrum of an ultrathin, uncapped 'quantum box' (QB) sample and compare it to results we have obtained previously on thick luminescent InGaN epilayers with a range of composition. While the epilayers resemble simple alloys, more or less, the QB sample reveals itself to consist of a two-phase mixture of InN and dilute InGaN alloy. The use of EXAFS to distinguish the local In environments of different InGaN-based heterostructures is likely to provide key information to unlock the puzzle of the origin of luminescence in these important commercial semiconductors. (C) 2002 Elsevier Science B.V. All rights reserved.
10 Dec 2002
TL;DR: In this paper, the influence of In surface segregation on InGaN/GaN QW properties was investigated both experimentally and theoretically, and it was shown that the influence can increase the sensitivity of electron and hole wave functions to the interface potential profiles.
Abstract: InGaN/GaN quantum wells (QWs) are very efficient visible light emitters in the blue-green wavelength range. However, the external quantum efficiency of InGaN based light emitting diodes (LEDs) decreases at longer wavelengths. This is mainly due to the presence of a very large piezoelectric field that strongly reduces the oscillator strength via a giant quantum confined Stark effect (QCSE). Another consequence of this QCSE is to increase the sensitivity of the electron and hole wave functions to the interface potential profiles. In the present paper, we investigate both experimentally and theoretically the influence of In surface segregation on InGaN/GaN QW properties.
10 Dec 2002
TL;DR: In this paper, the InAs/(Al,Ga)Sb material system was investigated in real-time using reflection high-energy electron diffraction (RHEED) measurements and the results indicated that the composition and therefore the band profile of InAs/AlSb heterostructures are strongly affected by indium surface segregation at InAs interfaces.
Abstract: It is now well established that In surface segregation prevents the formation of abrupt interfaces for In containing III-V heterostructures. Despite the drastic effects of In surface segregation on the actual potential profiles at quantum-well interfaces, only scarce results are available for the InAs/(Al,Ga)Sb material system. However, this material system has recently gained much technological interest, in particular because it is well suited for the achievement of room-temperature quantum-well laser diodes emitting in the 3-5 /spl mu/m mid-infrared spectral domain. The purpose of this communication is to show that In surface segregation can be evidenced in real-time during the growth of AlSb on InAs(Sb) by MBE using reflection high-energy electron diffraction (RHEED). The. interface width deduced from RHEED measurements (five monolayers (/spl plusmn/1 ML) for example at a standard growth temperature of 430/spl deg/C) agrees very well with the one observed by high-resolution transmission electron microscopy. Moreover, the influence of growth parameters on the In segregation length (/spl omega/) at the AlSb on InAs(Sb) interface and on the associated segregation ratio R = e/sup -1//spl omega// can easily be evaluated from RHEED measurements. The In segregation length (/spl omega/) is found to increase with the growth temperature (from /spl ap/5 to 15 ML in the 430-520/spl deg/C temperature range) as expected for a kinetically limited surface segregation phenomenon. The associated segregation ratio R varies from 0.8 to 0.9. These results indicate that the composition and therefore the band profile of InAs/AlSb heterostructures are strongly affected by indium surface segregation at AlSb on InAs interfaces.
TL;DR: In this article, the authors proposed an original model for electron-hole pair recombination in InGaN/GaN quantum systems, combining the effects of internal electric fields and of carrier localization on a nanometer-scale.
Abstract: Recombination dynamics in a variety of InGaN/GaN quantum systems has been studied by time resolved photoluminescence (PL). We have discovered that the time-decay of PL exhibits a scaling law: the nonexponential shape of this decay is preserved for quantum wells and quantum boxes of various sizes while their decay time varies over several orders of magnitude. To explain these results, we propose an original model for electron-hole pair recombination in these systems, combining the effects of internal electric fields and of carrier localization on a nanometer-scale. These two intricate effects imply a separate localization of electrons and holes. Such a microscopic description accounts very well for both the decays shape and the scaling law.
TL;DR: In this paper, it was shown that the exciton oscillator strength decreases dramatically with increase of the QW width in a GaN/Al 0.07Ga0.93N system.
Abstract: We have found experimentally that the exciton oscillator strength decreases dramatically with increase of the QW width in a GaN/Al0.07Ga0.93N system. The collapse of the oscillator strength is a manifestation of the polarisation field effect, as confirmed by our variational calculation. We find that only excitons in very thin quantum wells have an oscillator strength exceeding that of the exciton in bulk GaN.