Showing papers by "Jan Misiewicz published in 2005"
TL;DR: In this paper, the authors show that the oscillation features (OFs) usually observed in photoreflectance (PR) spectra of GaAs-based structures grown on the n-type GaAs substrate below the GaAs fundamental gap could be eliminated completely by applying the contactless electroreflectance (CER) instead of PR.
Abstract: In this letter, we show that the oscillation features (OFs) usually observed in photoreflectance (PR) spectra of GaAs-based structures grown on the n-type GaAs substrate below the GaAs fundamental gap could be eliminated completely by applying the contactless electroreflectance (CER) instead of PR. This finding confirms that the origin of OFs is the modulation of the refractive index in the sample due to the generation of additional carriers by the modulated pump beam. In the case of CER spectroscopy, any additional carriers are not generated during the modulation hence CER spectra are free of OFs. This advantage of CER spectroscopy is very important in investigations of all structures for which OFs are present in PR spectra. In order to illustrate this advantage of CER spectroscopy we show PR and CER spectra measured first for the GaAs epilayer and next for more complicated steplike GaInNAsSb∕GaNAs∕GaAs quantum well structures.
39 citations
TL;DR: In this article, the authors used secondary ion mass spectrometers, high-resolution x-ray diffraction, electroreflectance (ER) spectroscopy, and photoluminescence (PL) measurements to examine the optical and electronic properties and any interactions between the elements.
Abstract: GaNAs(Sb) layers were grown by solid-source molecular-beam epitaxy utilizing a radio frequency (rf) nitrogen plasma source. The samples contained less nitrogen and antimony (0.5%–0.8% N and ⩽2% Sb) than in previous studies and were examined for their optical and electronic properties and any interactions between the elements. Secondary-ion-mass spectrometry, high-resolution x-ray diffraction, electroreflectance (ER) spectroscopy, and photoluminescence (PL) measurements were used to study those properties. We found that the addition of small amounts of antimony enhanced nitrogen incorporation into GaAs, similar to other studies that used 5–15× the mole fraction of antimony. The nitrogen concentration increased with increasing antimony flux. PL measurements indicated an improvement in optical quality with increasing nitrogen and antimony concentrations—contrary to the belief that adding more nitrogen necessarily degrades material quality. We collected and simulated ER spectra to examine the general band pro...
35 citations
TL;DR: In this paper, the ground-state wetting layer quantum well transition was attributed to the ground state wetting layers and the spectral position of the latter is independent of the nominal InAs layer thickness in contrast to quantum-dash emission peak.
Abstract: Photoluminescence and photoreflectance measurements have been performed to investigate molecular-beam-epitaxy-grown InAs/InGaAlAs/InP structures with different-size InAs quantum dashes. Optical features related to all relevant parts of the structure have been detected and recognized, including a line which has been attributed to the ground-state wetting layer quantum well transition. The spectral position of the latter is independent of the nominal InAs layer thickness in contrast to quantum-dash emission peak, which shifts sequentially to the red due to an increase of the islands’ size. The interpretation has been supported by energy level calculations showing that the wetting layer has to be approximately 2 ML thick and that only one state is confined in such a thin well for each kind of carriers, i.e., electrons, heavy, and light holes.
32 citations
TL;DR: In this paper, a screw-like polarization of the medium during the interaction of two circularly polarized coherent bicolour beams was proposed and discovered for GaN nanocrystallites embedded in a silica xerogel matrix.
Abstract: Circularly polarized optical poling was proposed and discovered for GaN nanocrystallites embedded in a silica xerogel matrix. The method consists of the creation of screw-like polarization of the medium during the interaction of two circularly polarized coherent bicolour beams. It was shown that doping of the GaN nanocrystallites by Tb3+ and Eu3+ ions leads to substantial enhancement of the electrogyration. The effect observed is a consequence of the superposition of nanoconfined effects and the contribution of the localized rare-earth 4f levels. The role of the anharmonic electron–phonon interaction is discussed. The photoluminescence and cathodoluminescence spectra of the GaN composites were investigated. It was demonstrated that the Eu-doped nanocrystallites give a substantially higher effect of the electrogyration compared to the Tb-doped and non-doped ones.
27 citations
TL;DR: In this article, the photoreflectance (PR) features related to ground and excited state transitions have been clearly observed and the experimental data have been compared with the calculations in the envelope function formalism taking account of strain.
Abstract: GaN0.02As0.87Sb0.11∕GaAs single-quantum wells have been investigated by photoreflectance (PR) at room temperature. PR features related to the ground and excited state transitions have been clearly observed. The experimental data have been compared with the calculations in the envelope function formalism taking account the effect of strain. The band gap lowering and the increase in the electron effective mass due to the incorporation of nitrogen atoms into GaAsSb have been included. Excellent agreement between experimental data and calculation results have been found for band structure Type-I with the conduction-band offset ratio of 50%.
21 citations
TL;DR: In this article, a new approach to fabricate GaN films has been proposed, where GaN powder was synthesized by reacting gallium oxide (Ga 2 O 3 ) with ammonia (NH 3 ) using a horizontal quartz reactor.
20 citations
TL;DR: In this article, the energy level structure of a step-like GaInNAsSb∕GaNAs ∕GaAs quantum well has been investigated by photoreflectance (PR) spectroscopy and was analyzed by theoretical calculations.
Abstract: The energy level structure of a step-like GaInNAsSb∕GaNAs∕GaAs quantum well (QW) has been investigated by photoreflectance (PR) spectroscopy and was analyzed by theoretical calculations. In the active region of this structure, i.e., GaInNAsSb∕GaNAs QW, we have observed PR resonances related higher order QW transitions in addition to the ground state transition. Based on calculations from experimental data, we have found that the electron effective mass in the active QW is 0.12m0 and the conduction band offset for GaInNAsSb∕GaAs interface is about 0.85. The emission observed from this structure at 10K has a small Stokes shift (i.e., 6meV and <2meV for as-grown and annealed structures, respectively) and is without the exponential-like tail at the low-energy side. Hence, we conclude that the incorporation of Sb atoms into GaInNAs alloy helps to achieve QW structures which emit light at longer wavelength and have quite narrow emission line and small Stokes shift.
19 citations
TL;DR: In this paper, a xerogel, doped with lanthanide ions (erbium, terbium and europium), embedded in porous anodic alumina (PAA) has been fabricated and their optical and electrical properties have been studied.
16 citations
TL;DR: In this article, the above-bandgap photoreflectance (PR) features observed for GaN layers and undoped AlGaN∕GaN transistor structures have been analyzed.
Abstract: Below-bandgap photoreflectance (PR) features observed for GaN layers and undoped AlGaN∕GaN transistor structures have been analyzed in this letter. In addition to PR signal associated with the interference oscillations a strong PR feature at ∼3.37eV has been resolved for some AlGaN∕GaN structures. This feature has been attributed to an electron transition between the valence band and a donorlike state located ∼50meV below the conduction band. An absorptiontype experiment, such as PR spectroscopy, makes it possible to observe such a transition because this donorlike state is ionized by the strong internal electric field existing in the GaN layer at the AlGaN∕GaN interface. The existence of this electric field with a magnitude of ∼210kV∕cm has been confirmed by the observation of GaN-related Franz-Keldysh oscillations in the PR spectra. Obtained results show that donorlike states located ∼50meV below the conduction band are one of the sources of high concentration of the two dimensional electron gas in undo...
14 citations
TL;DR: In this article, a simple method of GaN nanocrystallites synthesis is presented, and the structure and morphology of the nanocrystites are investigated using XRD and TEM measurements.
14 citations
TL;DR: In this article, the authors investigated the emissions of Nd 3+ ions in the red and near infrared in silica gel films containing quantum dots of silicon, with comparison to those in pure silica.
TL;DR: In this article, the photoluminescence (PL) spectra obtained from as-grown and annealed GaN0.027As0.863Sb0.11∕GaAs single quantum wells (SQWs) were investigated.
Abstract: We have investigated characteristics of photoluminescence (PL) spectra obtained from as-grown and annealed GaN0.027As0.863Sb0.11∕GaAs single quantum wells (SQWs). For the as-grown SQW at low temperature ( 150K), the PL peak is attributed to free-carrier recombination.
TL;DR: In this paper, the influence of interdiffusion of atoms between well and barrier layers on the ground state exciton binding energy has been investigated as a function of the well width, for different quaternary material compositions.
TL;DR: In this article, photoreflectance and photoluminescence measurements were performed on the ensemble of self assembled InAs/GaAs quantum dots designed to emit at 1.3 μm.
TL;DR: In this paper, photoreflectance features related to optical transitions in the active part of the step-like DQW structure, as well as optical transitions between hole and electron levels confined above the SLB have been clearly observed and analyzed.
Abstract: Photoreflectance (PR) spectroscopy has been applied to study of step-like GaInNAs/GaInNAs/GaAs double quantum well (DQW) structures grown by molecular beam epitaxy PR features related to optical transitions in the active part of the step-like QW structure, ie GaInNAs/GaInNAs QW, as well as PR features related to transitions above the step-like barrier (SLB) have been clearly observed and analysed in this paper The analysis of the QW transitions gives information about the number of confined states in the active part of the step-like QW structure In addition, the analysis of the second portion of PR signal gives information about the band gap energy of the SLB and optical transitions between hole and electron levels confined above the SLB
TL;DR: The observed AlGaN-related transition has been identified as a band-to-band absorption in the layer being in under a strong built-in electric field, attributed to an increase in the surface potential for Al GaN layer due to the rise of Al mole fraction.
02 Aug 2005
TL;DR: The photoreflectance features related to light hole (LH) and heavy hole (HH) transitions are well separated (∼31 meV) and can be precisely analyzed as discussed by the authors.
Abstract: Due to the tensile strain in the GaN0.02As0.98 layer, photoreflectance features related to light hole (LH) and heavy hole (HH) transitions are well separated (∼31 meV) and can be precisely analyzed. A careful analysis of the experimental data has shown that at low temperatures both the LH and the HH transitions are composed of two resonances. The first is related to excitonic absorption and the second related to band‐to‐band absorption. The exciton binding energies, determined from the splitting of the two contributions, are ∼4.7 meV and ∼6.2 meV for LH and HH excitons, respectively.
TL;DR: It has been shown that Franz–Keldysh oscillations related to GaAs cap layer are clearly observed in CER and disappear in PR at strong modulation conditions due to an effective flattering of the surface band bending during PR measurements.
Journal Article•
TL;DR: In this paper, the room temperature photoreflectance (PR) spectroscopy was used to investigate thick GaN epitaxial layers, which were grown by hydride vapour phase epitaxy (HVPE) technique.
Abstract: The room temperature photoreflectance (PR) spectroscopy was used to investigate thick GaN epitaxial layers. The GaN layers were grown by hydride vapour phase epitaxy (HVPE) technique and compared to thin GaN layer grown by metalorganic vapour phase epitaxy (MOVPE) technique on AlN buffer layer. We observed energy red shift of the PR resonance for HVPE GaN layers compared with MOVPE GaN layer. This blue shift is due to reduction of the strain in HVPE layer. In addition, weak PR features related to Franz–Keldysh oscillations (FKO) have been observed. The electric field determined from the FKO period is 28 and 71 kV/cm for MOVPE and HVPE layers, respectively.
TL;DR: In this paper, the effect of rapid thermal annealing (RTA) on InGaAsP-based quantum wells (QWs) which are the active part of a laser structure tailored at 1.5 μm was studied.
Abstract: Photoreflectance (PR) and photoluminescence (PL) spectroscopies have been used to study the effect of the rapid thermal annealing (RTA) on InGaAsP-based quantum wells (QWs) which are the active part of a laser structure tailored at 1.5 μm. In the case of PL, it has been observed that the RTA enhances PL intensity and tunes the emission wavelength of the laser structure to blue. In case of PR due to its absorption character, we were able to study QW transitions related to excited states, besides the fundamental transition observed in PL. In addition, optical transitions related to other part of the laser structure have been observed in PR. It has been shown that there exists a critical annealing temperature (720 °C) where the energy shift appears. We have observed a blueshift for both the ground and excited state transitions, but in the case of the ground state transitions the blueshift has been found to be bigger. The magnitude of this blueshift has been found to change linearly from 0 to ∼15 meV with the rise of temperature from 720 to 780 °C. Below 720 °C no significant change in the energy of the QW transitions is observed. In the case of PR transitions related to the other part of the laser structure, i.e., the quaternary InGaAsP barriers, it has been observed that after annealing PR features associated with these layers rather do not shift, they change only their line-shape. Also, it has been shown that RTA does not destroy the optical quality of the samples.
Journal Article•
TL;DR: In this paper, photoreflectance (PR) and contactless electroreflectance (CER) were used for investigation of optical properties of InGaAsP quantum well with infrared emission at 1.55 µm.
Abstract: Modulation spectroscopy, i.e., photoreflectance (PR) and contactless electroreflectance (CER) are very powerful techniques to investigate optical properties of nanostructures. These techniques together with photoluminescence spectroscopy were used for investigation of optical properties of InGaAsP quantum well with infrared emission at 1.55 µm. Samples used in this study were grown by gas source molecular beam epitaxy (MBE) on n-doped (100) InP substrate. Based on the numerical calculations the origin of observed optical transitions has been explained and the energy structure of the investigated samples has been proposed.
02 Aug 2005
TL;DR: In this article, photoreflectance transitions of undoped and Si-doped AlGaN/GaN heterostructures were investigated at room temperature in the presence of a two-dimensional electron gas at the interface.
Abstract: Photoreflectance (PR) transitions of undoped and Si‐doped AlGaN/GaN heterostructures are investigated at room temperature In the case of an undoped heterostructure, PR features associated with transitions in GaN and AlGaN layers are observed In the case of a Si‐doped heterostructure, besides GaN‐ and AlGaN‐related absorption, a broad PR feature associated with the presence of a two dimensional electron gas at the AlGaN/GaN interface is clearly seen
Journal Article•
TL;DR: In this article, single quantum wells with different distance from a delta doped layer have been investigated by using contactless electroreflectance (CER) spectroscopy, and the oscillator strength of optical transitions and the value of the built-in electric field have been determined from CER spectra.
Abstract: As/GaAs single quantum wells with different distance from a delta doped layer havebeen investigated by using contactless electroreflectance (CER) spectroscopy. The oscillatorstrength of optical transitions and the value of the built-in electric field have been determinedfrom CER spectra. Obtained results have been compared with theoretical calculations preformedin the framework of the effective mass approximation. In order to accurately find the wavefunctionsof electrons and holes confined in the quantum well embedded in the built-in electric field,the time-dependent Schrodinger equation has been solved. Keywords: quantum well, contactless electroreflectance, built-in electric field, delta-doping.
01 Jan 2005
TL;DR: In this paper, photoreflectance (PR) spectra were collected from the quantum well (QW) structures and the energy transitions were analyzed by theoretical calculations, and the authors found that Q c ≈ 0.5.
Abstract: Heterojunction band offsets of GaNAsSb/GaAs, GaInNAsSb/GaAs, and GaInNAsSb/GaNAs/GaAs quantum well (QW) structures were measured by photoreflectance (PR) spectroscopy. These samples were grown by solid-source molecular beam epitaxy using a radio-frequency nitrogen plasma source. PR spectra were collected from the QW structures and the energy transitions were obtained. The experimental data of the QW energy transitions were analyzed by theoretical calculations. Using predetermined values such as QW thickness and composition, unknown factors such as the heterojunction band offsets were able to be determined. For the GaN 0.02 As 0.87 Sb 0.11 /GaAs structure, we found that Q c ≈0.5. For Ga 0.62 In 0.38 N 0.026 As 0.954 Sb 0.02 /GaAs, we found that Q c ≈0.8. This value is similar to the antimony free dilute-nitride material GaInNAs since the small amount of antimony does not affect the band offsets. For the technologically important Ga 0.61 In 0.39 N 0.023 As 0.957 Sb 0.02 /GaN 0.027 As 0.973 /GaAs laser structure, we found that the GaInNAsSb/GaNAs QW had a conduction band offset of 144 meV and a valence band offset of 127 meV. With a greater understanding of the band structure, more advanced GaInNAsSb laser devices can be obtained.