Bottom-up Photonic Crystal Lasers

The directed growth of III–V nanopillars is used to demonstrate bottom-up photonic crystal lasers. Simultaneous formation of both the photonic band gap and active gain region is achieved via catalyst-free selective-area metal–organic chemical vapor deposition on masked GaAs substrates. The nanopillars implement a GaAs/InGaAs/GaAs axial double heterostructure for accurate, arbitrary placement of gain within the cavity and lateral InGaP shells to reduce surface recombination. The lasers operate single-mode at room temperature with low threshold peak power density of ~625 W/cm^2. Cavity resonance and lasing wavelength is lithographically defined by controlling pillar pitch and diameter to vary from 960 to 989 nm. We envision this bottom-up approach to pillar-based devices as a new platform for photonic systems integration

Optical characterization of AlAsSb digital alloy and random alloy on GaSb

III-(As, Sb) alloys are building blocks for various advanced optoelectronic devices, but the growth of their ternary or quaternary materials are commonly limited by spontaneous formation of clusters and phase separations during alloying. Recently, digital alloy growth by molecular beam epitaxy has been widely adopted in preference to conventional random alloy growth because of the extra degree of control offered by the ordered alloying. In this article, we provide a comparative study of the optical characteristics of AlAsSb alloys grown lattice-matched to GaSb using both techniques. The sample grown by digital alloy technique showed stronger photoluminescence intensity, narrower peak linewidth, and larger carrier activation energy than the random alloy technique, indicating an improved optical quality with lower density of non-radiative recombination centers. In addition, a relatively long carrier lifetime was observed from the digital alloy sample, consistent with the results obtained from the photoluminescence study

Carrier localization and in-situ annealing effect on quaternary Ga1-xInxAsySb1-y/GaAs quantum wells grown by Sb pre-deposition

Using temperature-dependent photoluminescence spectroscopy, we have investigated and compared intrinsic InGaAs, intrinsic GaInAsSb, and p-i-n junction GaInAsSb quantum wells (QWs) embedded in GaAs barriers. Strong carrier localization inside the intrinsic GaInAsSb/GaAs QW has been observed together with its decrease inside the p-i-n sample. This is attributed to the effect of an in-situ annealing during the top p-doped AlGaAs layer growth at an elevated temperature of 580 degrees C, leading to Sb-atom diffusion and even atomic redistribution. High-resolution X-ray diffraction measurements and the decrease of both maximum localization energy and full delocalization temperature in the p-i-n QW sample further corroborated this conclusion. (C) 2013 American Institute of Physics. (http://dx.doi.org/10.1063/1.4795866

Electro-optical and lasing properties of hybrid quantum dot/quantum well material system for reconfigurable photonic devices

We characterize the electro-optical and lasing properties of a hybrid material consisting of multiple InAs quantum dot (QD) layers together with an InGaAs quantum well (QW) grown on a GaAs substrate. Over 40 nm Stark shift of the InGaAs QW leading to 9 dB extinction ratio was demonstrated. Lasing operation at the QD first excited state transition of 1070 nm was achieved and together with < 10 ps absorption recovery the system shows promise for high-speed mode-locked lasers and electro-modulated lasers. (C) 2013 American Institute of Physics. (http://dx.doi.org/10.1063/1.4791565

Review Article: Molecular Beam Epitaxy of Lattice-Matched InAlAs and InGaAs Layers on InP (111)A, (111)B, and (110)

For more than 50 years, research into III–V compound semiconductors has focused almost exclusively on materials grown on (001)-oriented substrates. In part, this is due to the relative ease with which III–Vs can be grown on (001) surfaces. However, in recent years, a number of key technologies have emerged that could be realized, or vastly improved, by the ability to also grow high-quality III–Vs on (111)- or (110)-oriented substrates These applications include: next-generation field-effect transistors, novel quantum dots, entangled photon emitters, spintronics, topological insulators, and transition metal dichalcogenides. The first purpose of this paper is to present a comprehensive review of the literature concerning growth by molecular beam epitaxy (MBE) of III–Vs on (111) and (110) substrates. The second is to describe our recent experimental findings on the growth, morphology, electrical, and optical properties of layers grown on non-(001) InP wafers. Taking InP(111)A, InP(111)B, and InP(110) substrates in turn, the authors systematically discuss growth of both In0.52Al0.48As and In0.53Ga0.47As on these surfaces. For each material system, the authors identify the main challenges for growth, and the key growth parameter–property relationships, trends, and interdependencies. The authors conclude with a section summarizing the MBE conditions needed to optimize the structural, optical and electrical properties of GaAs, InAlAs and InGaAs grown with (111) and (110) orientations. In most cases, the MBE growth parameters the authors recommend will enable the reader to grow high-quality material on these increasingly important non-(001) surfaces, paving the way for exciting technological advances

Strongly coupled slow-light polaritons in one-dimensional disordered localized states

Cavity quantum electrodynamics advances the coherent control of a single quantum emitter with a quantized radiation field mode, typically piecewise engineered for the highest finesse and confinement in the cavity field. This enables the possibility of strong coupling for chip-scale quantum processing, but till now is limited to few research groups that can achieve the precision and deterministic requirements for these polariton states. Here we observe for the first time coherent polariton states of strong coupled single quantum dot excitons in inherently disordered one-dimensional localized modes in slow-light photonic crystals. Large vacuum Rabi splittings up to 311 {\mu}eV are observed, one of the largest avoided crossings in the solid-state. Our tight-binding models with quantum impurities detail these strong localized polaritons, spanning different disorder strengths, complementary to model-extracted pure dephasing and incoherent pumping rates. Such disorder-induced slow-light polaritons provide a platform towards coherent control, collective interactions, and quantum information processing.Comment: 17 pages, 5 figures and supplementary informatio

Coulomb effect inhibiting spontaneous emission in charged quantum dot

We investigate the emission dynamics of InAs/GaAs quantum dots (QDs) coupled to an InGaAs quantum well in a tunnel injection scheme by means of time-resolved photoluminescence. Under high-power excitation we observe a redshift in the QD emission of the order of 20 meV. The optical transition intensity shows a complex evolution, where an initial plateau phase is followed by an increase in intensity before a single-exponential decay. We attribute this behavior to the Coulomb interactions between the carriers in a charged QD and corroborate the experimental results with both a rate equation model and self-consistent eight-band k.p calculations. (C) 2010 American Institute of Physics. (doi:10.1063/1.3484143

Impact of Arsenic Species on Self-Assembly of Triangular and Hexagonal Tensile-Strained GaAs(111)A Quantum Dots

We use dimeric arsenic (As2) or tetrameric arsenic (As4) during molecular beam epitaxy to manipulate the structural and optical properties of GaAs(111)A tensile-strained quantum dots (TSQDs). Choice of arsenic species affects nucleation and growth behavior during TSQD self-assembly. Previously, epitaxial GaAs(111)A TSQDs have been grown with As4, producing TSQDs with a triangular base, and \u27A-step\u27 edges perpendicular to the three 1̅1̅2 directions. We demonstrate that using As2 at low substrate temperature also results in triangular GaAs(111)A TSQDs, but with \u27B-step\u27 edges perpendicular to the three 112̅ directions. We can therefore invert the crystallographic orientation of these triangular nanostructures, simply by switching between As4 and As2. At higher substrate temperatures, GaAs(111)A TSQDs grown under As2 develop with a hexagonal base. Compared with triangular dots, the higher symmetry of hexagonal TSQDs may reduce fine-structure splitting on this (111) surface, a requirement for robust photon entanglement. Regardless of shape, GaAs(111)A TSQDs grown under As2 exhibit superior optical quality

Flexbility of Ga-containing type-II superlattice for long-wavelength infrared detection

In this paper, the flexibility of long-wavelength Type-II InAs/GaSb superlattice (Ga-containing SL) is explored and investigated from the growth to the device performance. First, several samples with different SL period composition and thickness are grown by molecular beam epitaxy. Nearly strain-compensated SLs on GaSb exhibiting an energy band gap between 105 to 169 meV at 77K are obtained. Second, from electronic band structure calculation, material parameters are extracted and compared for the different grown SLs. Finally, two p-i-n device structures with different SL periods are grown and their electrical performance compared. Our investigation shows that an alternative SL design could potentially be used to improve the device performance of diffusion-limited devices for long-wavelength infrared detection

Energy-sensitive GaSb/AlAsSb separate absorption and multiplication avalanche photodiodes for X-Ray and gamma-ray detection

Demonstrated are antimony‐based (Sb‐based) separate absorption and multiplication avalanche photodiodes (SAM‐APDs) for X‐ray and gamma‐ray detection, which are composed of GaSb absorbers and large bandgap AlAsSb multiplication regions in order to enhance the probability of stopping high‐energy photons while drastically suppressing the minority carrier diffusion. Well‐defined X‐ray and gamma‐ray photopeaks are observed under exposure to 241Am radioactive sources, demonstrating the desirable energy‐sensitive detector performance. Spectroscopic characterizations show a significant improvement of measured energy resolution due to reduced high‐peak electric field in the absorbers and suppressed nonradiative recombination on surfaces. Additionally, the GaSb/AlAsSb SAM‐APDs clearly exhibit energy response linearity up to 59.5 keV with a minimum full‐width half‐maximum of 1.283 keV. A further analysis of the spectroscopic measurement suggests that the device performance is intrinsically limited by the noise from the readout electronics rather than that from the photodiodes. This study provides a first understanding of Sb‐based energy‐sensitive SAM‐APDs and paves the way to achieving efficient detection of high‐energy photons for X‐ray and gamma‐ray spectroscopy