A. Rudra

Island formation in ultra-thin InAs/InP quantum wells grown by chemical beam epitaxy

We have studied the effect of growth interruptions on 2‐monolayers‐thick InAs/InP strained quantum wells (QW) grown by chemical beam epitaxy. The main feature is the formation of up to 8‐monolayers‐thick InAs islands during As2 annealing of the QW. Their formation is characterized by a two to three dimensional transition of the reflection high‐energy electron diffraction pattern and multiple‐lines photoluminescence spectra. An increase of a short range roughness at the InP‐InAs interface due to As2 annealing of InP is also observed.

Bound-to-continuum terahertz quantum cascade laser with a single-quantum-well phonon extraction/injection stage

A terahertz quantum cascade laser design that combines a wide gain bandwidth, large photon-driven transport and good high-temperature characteristics is presented. It relies on a diagonal transition between a bound state and doublet of states tunnel coupled to the upper state of a phonon extraction stage. The high optical efficiency of this design enables the observation of photon-driven transport over a wide current density range. The relative tolerance of the design to small variations in the barrier thicknesses made it suitable for testing different growth techniques and materials. In particular, we compared the performances of devices grown using molecular-beam epitaxy with those achieved using organometallic chemical vapor deposition. The low-threshold current density and the high slope efficiency makes this device an attractive active region for the development of single-mode quantum cascade lasers based on third-order-distributed feedback structures. Single-mode, high power was achieved with good continuous and pulsed wave operation.

Integration of site-controlled pyramidal quantum dots and photonic crystal membrane cavities

Deterministic integration of site-controlled InGaAs/GaAs quantum dots (QDs) with photonic crystal cavities is demonstrated. Fine adjustment of QD position (within ~10 nm) and emission energy (few meV) allows construction of coupled QD systems.

Wavelength and loss splitting in directly coupled photonic-crystal defect microcavities

Coupling between photonic-crystal defect microcavities is observed to result in a splitting not only of the mode wavelength but also of the modal loss. It is discussed that the characteristics of the loss splitting may have an important impact on the optical energy transfer between the coupled resonators. The loss splitting--given by the imaginary part of the coupling strength--is found to arise from the difference in diffractive out-of-plane radiation losses of the symmetric and the antisymmetric modes of the coupled system. An approach to control the splitting via coupling barrier engineering is presented.

Site-Controlled InGaAs Quantum Dots with Tunable Emission Energy

Semiconductor quantum-dot (QD) systems offering perfect site control and tunable emission energy are essential for numerous nanophotonic device applications involving spatial and spectral matching of dots with optical cavities. Herein, the properties of ordered InGaAs/GaAs QDs grown by organometallic chemical vapor deposition on substrates patterned with pyramidal recesses are reported. The seeded growth of a single QD inside each pyramid results in near-perfect (<10 nm) control of the QD position. Moreover, efficient and uniform photoluminescence (inhomogeneous broadening <10 meV) is observed from ordered arrays of such dots. The QD emission energy can be finely tuned by varying 1) the pyramid size and 2) its position within specific patterns. This tunability is brought about by the patterning of both the chemical properties and the surface curvature features of the substrate, which allows local control of the adatom fluxes that determine the QD thickness and composition.

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

Keywords: epitaxy ; nanotechnology ; photonics ; quantum dots ; self-assembly ; Pyramids ; Arrays ; Energy Reference EPFL-ARTICLE-150247doi:10.1002/smll.201000341View record in Web of Science Record created on 2010-08-04, modified on 2017-05-12

DYNAMICS OF ISLAND FORMATION IN THE GROWTH OF INAS/INP QUANTUM-WELLS

A thin InAs layer grown in a quasi-two-dimensional film over InP reorganizes into islands if left to anneal under arsine. This surface transformation is inhibited at lower arsine fluxes. With increasing temperature, the surface transformation is activated as long as the effective arsine coverage is sufficient.

Optical polarization anisotropy and hole states in pyramidal quantum dots

The authors present a polarization-resolved photoluminescence study of single semiconductor quantum dots (QDs) interconnected to quantum wires, measured both in a top geometry, and in a less conventional cleaved-edge geometry. Strong polarization anisotropy is revealed for all observed transitions, and it is deduced that closely spaced QD hole states exhibit nearly pure heavy-or light-hole character. These effects are attributed to the large aspect ratio of the dot shape.

Low threshold 1.55 mu m wavelength InAsP/InGaAsP strained multiquantum well laser diode grown by chemical beam epitaxy

By using chemical beam epitaxy at growth temperatures as low as 460–480 °C, we have overcome strain relaxation problems that prevented so far the successful use of InAsP quantum wells in 1.55 μm lasers. Five quantum well InAsP/InGaAsP horizontal cavity lasers showed 88% internal efficiency, 1.6 cm−1 losses per well, and 33 A/cm2 transparency current density per well, which equal or even surpass the best published characteristics for 1.55 μm wavelength lasers based on any material system. Moreover, up to 17 quantum wells were integrated in a strain-balanced laser, which showed equally good characteristics.

Photonic-crystal microcavity laser with site-controlled quantum-wire active medium

Site-controlled quantum-wire photonic-crystal microcavity laser is experimentally demonstrated using optical pumping. The single-mode lasing and threshold are established based on the transient laser response, linewidth narrowing, and the details of the non-linear power input-output characteristics. Average-power threshold as low as approximately 240 nW (absorbed power) and spontaneous emission coupling coefficient beta approximately 0.3 are derived.