Publications by Alok Rudra | EPFL Graph Search

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We discuss the growth of lattice matched GaInAs, GaInAsP and GaInAsP/GaInAs multiple quantum well structures for high speed laser applications. Optical cavities, including five 90 angstrom GaInAs quantum wells with GaInAsP barriers and waveguides showed a 4 K photoluminescence line width of 8.7 meV. Transmission electron microscopy and X-ray diffraction confirm the good control over the growth of these structures.

We present results on the polarization-resolved photoluminescence emitted from InGaAs/AlGaAs single quantum dots (QDs) grown in inverted tetrahedral pyramids. The emitted light was detected for two mutually perpendicular linear polarization directions in t ...

We have evaluated the structure of high-reflectivity InP/InGaAsP distributed Bragg reflectors grown by chemical-beam epitaxy at a growth rate of 3 mu m/h. Transmission electron microscopy combined with electron energy loss spectroscopy indicate lateral fluctuations in the GaInAsP alloy composition, clearly visible in the 490-510 degrees C growth temperature range, but less perceptible between 460 and 480 degrees C. In the higher temperature range, the modulation in composition shows a higher frequency along

The diffusivity of photogenerated electron-hole pairs in weakly disordered GaAs/AlGaAs V-groove quantum wires was measured using a photoluminescence (PL) time-of-flight technique. It is shown that the electron-hole pair diffusion is thermally activated above about 50 K. Exciton localization is observed in micro-PL (mu PL) spectra at low temperature. A reduction in the Stokes shift is found to accompany the increase in the diffusion coefficient. Nevertheless, localization-related features in the mu PL spectr

Pyramidal, site-controlled InGaAs/AlGaAs quantum dots (QDs) are studied by micro-photoluminescence (PL) spectroscopy in a magnetic field. The light-hole (LH) excitonic transitions exhibit diamagnetic shifts similar to those of their heavy-hole (HH) counterparts. From the evolution of the excitonic lines, effective g-factors of g = 1.7 and 0.4 for HH and LH neutral excitons are inferred. (c) 2007 Elsevier B.V. All rights reserved.

We used optical pumping by the Vanderbilt free-electron laser and the technique of internal photoemission to measure with high accuracy the conduction-band discontinuity of semiconductor heterojunction interfaces. The experiment is the first application to our knowledge of a free-electron laser to interface research.

We study a specific type of lifetime broadening resulting in the well-known exponential "Urbach tail" density of states within the energy gap of an insulator. After establishing the frequency and temperature dependence of the Urbach edge in GaAs quantum we ...

We have studied systems of asymmetric coupled GaAs V-groove quantum wires, in which the electrons and holes are injected into different wires. Our experimental results indicate efficient electron and hole tunneling, despite a 7 nm thick AlGaAs tunnel barrier. Temperature dependent electroluminescence exhibit clear effects of tunneling up to room temperature but cannot distinguish electron/hole tunneling from exciton tunneling.

We investigated experimentally 1D and 2D arrays of coupled L3 photonic crystal cavities. The optical modes of the coupled cavity arrays are fed by a site-controlled quantum wire light source. By performing photoluminescence measurements and relying on near ...

A high-reflectance GaInP/GaAs distributed Bragg reflector (DBR) was grown by chemical beam epitaxy (CBE). The mirror consists of 40 pairs of alternating layers and was designed for a centre wavelength of 980 nm, resulting in a total thickness of 5.8 mum. Highly stable growth conditions led to a maximum reflectance of 0.99 and to a variation in the centre wavelength of only 5 nm over the 2'' (50.8 mm) wafer. Transmission electron microscopy and X-ray diffraction measurements confirmed the vertical uniformity

Valence- and conduction-band offsets can be induced at GaAs(100) polar homojunctions by means of ultrathin Si intralayers. The microscopic interface dipole responsible for the creation of such offsets can be varied by changing the Si intralayer thickness; the consequently variable band discontinuities represent a tunable parameter with potential applications in band-gap engineering. Even though the existence and the direction of these discontinuities are in agreement with theoretical predictions, the existi

Dense (10(10) cm(-2)) quantum dots (QDs) were grown in inverted pyramidal recesses by OMCVD. The high uniformity of the QD arrays is demonstrated by micro-photoluminescence spectra having linewidth as small as 6.5 meV and AFM measurements.

We report on the first observation of both confined optical phonons and interface phonons in a single strained InAs quantum well grown on InP. Quasi resonant Raman measurements allow for the observation of interface modes. Informations about the mismatch induced strain in the InAs layer are obtained. The effect of the strain and the confinement on the longitudinal and transverse optical InAs modes are estimated.

We investigated the composition and optical properties of GaInAsN/GaAs single quantum wells (QWs) grown on vicinal-(001) GaAs substrates using metallorganic vapor phase epitaxy with modulated nitrogen-precursor flux. A significant enhancement in N incorporation and photoluminescence efficiency is achieved with such optimized QW structures. Possible mechanisms of the observed increase in N uptake and reduction in defect density, related to the substrate vicinality, are discussed.

Semiconductor nanowires (NWs) in horizontal configuration could provide a path for scalable NW-based devices. Bottom-up large-scale manufacturing of these nanostructures by selective area epitaxy (SAE) relies on precise nanopatterning of various shapes on ...

We report on the growth of barrier, reservoir and quantum well electron transfer (BRAQWET) structures using chemical beam epitaxy. The photoluminescence spectra of the structures are affected by the bias voltage. The QW emission line is extinguished at positive bias and the barrier emission line is extinguished at negative bias. These effects might be used for the BRAQWETs characterization.

Coupling of L-type photonic-crystal (PhC) cavities in a geometry that follows inherent cavity field distribution is exploited for demonstrating large mode splitting of up to similar to 10-20 nm (similar to 15-30 meV) near 1 mu m wavelength. This is much la ...

Site-controlled InGaAsN quantum wires (QWRs) emitting at 1.3 lm at room temperature were grown on V-grooved GaAs substrates by modulated-flux metallorganic vapor phase epitaxy. The nonplanar substrate template is shown to enhance the nitrogen uptake, evidenced by a redshift in photoluminescence wavelength twice larger for the QWRs than for the adjacent quantum well regions. The mechanism of this increase in nitrogen incorporation efficiency, achieved without degradation in optical properties, is explained b

We demonstrate 2-mu m wavelength, wafer-fused InGa(Al)As/InP-AlGaAs/GaAs vertical-cavity surface-emitting lasers (VCSELs) emitting single-mode power of 0.5 mW at room-temperature with a threshold current of 4mA and side-mode suppression ratio of over 30 dB. Emission wavelength can be continuously tuned with current by similar to 5 nm without mode hopping with a tuning rate of 0.31 nm/mA. These features demonstrate the long wavelength VCSELs potential for gas sensing and other optical spectroscopy applicatio

Alok Rudra

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Growth of Gainas(P) and Gainasp/Gainas Mqw Structures by Cbe

Excited excitonic states observed in semiconductor quantum dots using polarization resolved optical spectroscopy

Record-Low Inhomogeneous Broadening of Site-Controlled Quantum Dots for Nanophotonics

Evaluation of InP/InGaAsP distributed Bragg reflectors grown by chemical-beam epitaxy

Diffusion of electron-hole pairs in disordered quantum wires

Magneto-photoluminescence of heavy- and light-hole excitons in site-controlled pyramidal quantum dots

Interface Measurements of Heterojunction Band Lineups with the Vanderbilt Free-Electron Laser

Measurements of the Electric Field of Zero-Point Optical Phonons in GaAs Quantum Wells Support the Urbach Rule for Zero-Temperature Lifetime Broadening

Electrolummescence of asymmetric coupled GaAs/AlGaAs V-groove quantum wires

1D and 2D arrays of coupled photonic crystal cavities with a site-controlled quantum wire light source

High-reflectance GaInP/GaAs distributed Bragg reflector

Artificial Band Discontinuities at GaAs Homojunctions

Dense (10(10) cm(-2)) Arrays of Ordered Quantum Dots with Narrow (< 10 meV) Photoluminescence Spectra

Raman study of a single InP/InAs/InP strained quantum well

High-quality 1.3 lm-wavelength GaInAsN/GaAs quantum wells grown by metalorganic vapor phase epitaxy on vicinal substrates

The implementation of thermal and UV nanoimprint lithography for selective area epitaxy

Chemical Beam Epitaxy and Photoluminescence Characteristics of Ingaasp/Inp Braqwet Modulators

Large mode splitting and lasing in optimally coupled photonic-crystal microcavities

Dilute nitride InGaAsN/GaAs V-groove quantum wires emitting at 1.3 μm wavelength at room temperature

2-μm wavelength range InGa(Al)As/InP-AlGaAs/GaAs wafer fused VCSELs for spectroscopic applications