Khaled Mnaymneh

Ultraclean Emission from InAsP Quantum Dots in Defect-Free Wurtzite InP Nanowires

We report on the ultraclean emission from single quantum dots embedded in pure wurtzite nanowires. Using a two-step growth process combining selective-area and vapor-liquid-solid epitaxy, we grow defect-free wurtzite InP nanowires with embedded InAsP quantum dots, which are clad to diameters sufficient for waveguiding at λ ~ 950 nm. The absence of nearby traps, at both the nanowire surface and along its length in the vicinity of the quantum dot, manifests in excitonic transitions of high spectral purity. Narrow emission line widths (30 μeV) and very-pure single photon emission with a probability of multiphoton emission below 1% are achieved, both of which were not possible in previous work where stacking fault densities were significantly higher.

Selective-area vapor-liquid-solid growth of tunable InAsP quantum dots in nanowires

A process is described where the position, size, and cladding of an InP nanowire with an embedded InAsP quantum dot are determined by design through lithography, processing, and growth. The vapor-liquid-solid growth mode on a patterned substrate is used to grow the InP core and defines the quantum dot size to better than ±2 nm while selective-area growth is used to define the cladding thickness. The clad nanowires emit efficiently in the range λ=0.95–1.15 μm. Photoluminescence measurements are used to quantify the dependence of the excitonic energy level structure on quantum dot size for diameters 10–40 nm.

Interplay between crystal phase purity and radial growth in InP nanowires

The interplay between crystal phase purity and radial growth in InP nanowires is investigated. By modifying the growth rate and V/III ratio, regions of high or low stacking fault density can be controllably introduced into wurtzite nanowires. It is found that regions with high stacking fault density encourage radial growth. Through careful choice of growth conditions pure wurtzite InP nanowires are then grown which exhibit narrow 4.2 K photoluminescence linewidths of 3.7 meV at 1.490 meV, and no evidence of emission related to stacking faults or zincblende insertions.

Wireless enabled multi gas sensor system based on photonic crystals

In this paper we introduce a multi gas sensor system based on refractive index changes in a 2D slab photonic crystal. The sensor is formed by a L3 resonant cavity sandwiched between two W1.06 waveguides in the photonic crystal. The sensor configuration is similar to an Add-Drop filter structure. The transmission spectrums of the sensor with different ambient refractive indices ranging from n = 1.0 to n = 1.1 are calculated. The simulation results show that a change in ambient RI of Δn = 0.0008 is apparent with a corresponding change in output wavelength of the sensor of 2.4 nm. The properties of the sensor are simulated using the 3D finite-difference time-domain (FDTD) method. The Q-factor of the sensor is also optimized, with highest values reaching over 30,000. The sensor system is hybrid integrated with a wireless RF chip which processes the sensor data and transmits them in effect turning the entire system into a wireless sensor mote.

Gas sensing using slow light in photonic crystal waveguides

We introduce a novel gas sensor based on photonic crystal (PhC) waveguides where the gas sensing is based on the interaction between the slow light mode and the gas. Specifically, when the refractive index of the photonic crystal waveguide changes (due to a change in gas), the slow light regime of the photonic crystal waveguide is affected and shifts in wavelength. We have performed experiments with Helium and Argon gases to confirm the operation of the sensor, with Air being used as reference gas. Results show that the slow light regime typically shifts by 0.6 nm for Helium and 0.05nm for Argon.

Bright Single InAsP Quantum Dots at Telecom Wavelengths in Position-Controlled InP Nanowires: The Role of the Photonic Waveguide

We report on the site-selected growth of bright single InAsP quantum dots embedded within InP photonic nanowire waveguides emitting at telecom wavelengths. We demonstrate a dramatic dependence of the emission rate on both the emission wavelength and the nanowire diameter. With an appropriately designed waveguide, tailored to the emission wavelength of the dot, an increase in the count rate by nearly 2 orders of magnitude (0.4 to 35 kcps) is obtained for quantum dots emitting in the telecom O-band, showing high single-photon purity with multiphoton emission probabilities down to 2%. Using emission-wavelength-optimized waveguides, we demonstrate bright, narrow-line-width emission from single InAsP quantum dots with an unprecedented tuning range of 880 to 1550 nm. These results pave the way toward efficient single-photon sources at telecom wavelengths using deterministically grown InAsP/InP nanowire quantum dots.

Strain analysis of highly scalable single InAs/InP quantum dots in a stress-sensitive environment

We perform an experimental and computational study of the effects of external stress and intermixing on single site-selected InAs/InP quantum dots in a highly scalable stress-sensitive environment. While such effects are well known for their ability to tune emission spectra, little is known on how they influence emission shell spacing, electron-hole effective mass renormalization, and the physical size of the embedded quantum dot, which are all important parameters affecting the intended functionality. We show excellent agreement between experiment and finite-element solutions of the coupled Navier and Schrodinger equations, including recent atomistic pseudopotential calculations in the literature. These results indicate that using single self-assembled quantum dots in highly scalable, stress-sensitive settings as active elements in future bottom-up nanosystems offers greater versatility to not only quantum information systems where they serve as scalable single-photon sources but also to ultra-sensing ca...

A semiconductor under insulator technology in indium phosphide

This letter introduces a semiconductor-under-insulator (SUI) technology in InP for designing strip waveguides that interface InP photonic crystal membrane structures. Strip waveguides in InP-SUI are supported under an atomic layer deposited insulator layer in contrast to strip waveguides in silicon supported on insulator. We show a substantial improvement in optical transmission when using InP-SUI strip waveguides interfaced with localized photonic crystal membrane structures when compared with extended photonic crystal waveguide membranes. Furthermore, SUI makes available various fiber-coupling techniques used in SOI, such as sub-micron coupling, for planar membrane III-V systems.

Scalable routes to single and entangled photon pair sources: Site-controlled InAs/InP quantum dots in photonic crystal microcavities

Self-assembled semiconductor quantum dots show great potential as efficient semiconductor-based non-classical light sources. However, due to the very nature of the self-assembled growth process, the characteristics of individual dots can vary widely and their spatial location is generally uncontrolled. Using a directed self-assembly process, the nucleation site of single quantum dots are designed through lithography. The site-control is used to facilitate the spatial alignment of single quantum dots to high finesse optical microcavities. The single dot-cavity device is a unique system to study the dot-cavity coupling where the presence of background emitters can be unambiguously ruled out.

Positioned growth of InP nanowires

We describe two different approaches to growing precisely positioned InP nanowires on InP wafers. Both of these approaches utilize the selective area growth capabilities of Chemical Beam Epitaxy, one using the Au catalysed Vapour-Liquid-Solid (VLS) growth mode, the other being catalyst-free. Growth is performed on InP wafers which are first coated with 20 nm of SiO2. These are then patterned using e-beam lithography to create nanometer scale holes in the SiO2 layer to expose the InP surface. For the VLS growth Au is then deposited into the holes in the SiO2 mask layer using a self-aligned lift-off process. For the catalyst-free growth no Au is deposited. In both cases the deposition of InP results in the formation of InP nanowires. In VLS growth the nanowire diameter is controlled by the size of the Au particle, whereas when catalyst-free the diameter is that of the opening in the SiO2 mask. The orientation of the nanowires is also different, <111>B when using Au particles and <111>A when catalyst-free. For the catalysed growth the effect of the Au particle can be turned off by modifying growth conditions allowing the nanowire to be clad, dramatically enhancing the optical emission from InAs quantum dots grown inside the nanowire.