1:30pm - 2:00pmInvited
Novel III-V Alloys for Infrared Photonic Devices
University of Surrey, United Kingdom
The incorporation of bismuth and/or nitrogen into III-V semiconductors offers a versatile way of tailoring the band structure and consequently the electronic and optical properties of semiconductors. This opens-up interesting and potentially exciting opportunities for applications in photonic, thermoelectric and spintronic devices. Adding Bi or N strongly reduces the bandgap, Eg, due to band anti-crossing in the valence, and conduction band, respectively. Bismuth also gives rise to a large spin-orbit splitting energy (ΔSO). This also opens up the possibility to grow (In)GaAsBi(N) alloys where the spin-orbit-splitting energy (ΔSO) is greater than Eg whilst pushing the corresponding emission wavelengths for GaAs and InP based alloys from the near-IR up to 6 µm while maintaining zero or low strain. Achieving the condition that ΔSO > Eg is highly significant as it inhibits the dominant efficiency-limiting loss processes in infrared lasers, namely Auger recombination, involving the generation of “hot” holes in the spin-orbit split-off band and inter-valence band absorption, where emitted photons are re-absorbed in the active region, which negatively impacts upon the efficiency and thermal stability of lasers and light emitting diodes. Similar opportunities also exist for type II GaAsN/GaAsBi zero net strain systems for photodetector applications. In this work we describe a combined experimental and theoretical study of these new alloys in the context of photonic device applications where flexible control of the band offsets and spin-orbit splitting is exploited for the design and realisation of efficient photonic devices operating in the infrared.
2:00pm - 2:15pmOral
Characterization of Wurtzite GaP-based Nanowires
Tata Institute of Fundamental Research, India
The ‘green gap’ – unavailability of efficient materials for green LEDs/lasers – is a major challenge in the semiconductor industry. Gallium phosphide (GaP) has zinc-blende structure in bulk with a bandgap lying in the green region (2.26 eV) but is indirect in nature. Contradictory theoretical predictions on wurtzite GaP suggest a direct bandgap (~2.2 eV)  or a pseudo-direct bandbap (optical transition between the valence and conduction band extremas, both at Γ-point, is forbidden) [2,3]. The few experimental reports are also contradictory. [4-6]
The wurtzite phase can be stabilized in nanowires. We have grown GaP nanowires in a metal-organic vapor phase epitaxy system using trimethylgallium and phosphine as precursors and a gold-based catalyst via the Vapour-Liquid-Solid process. The GaP nanowires were characterized using photoluminescence, X-ray diffraction, electron microscopy, and Raman scattering. Under optimized conditions, we obtained GaP nanowires in the wurtzite structure with hardly any stacking faults on Si substrates. These samples gave weak photoluminescence signal. We also grew GaP/AlGaP, InGaP/AlGaP and GaP/InGaP/GaP core-shell structures. An extensive study on the luminescence from these GaP-based core-shell structures of different indium and aluminum contents was done to understand the band-structure and band-alignment of these materials. We also attempted to grow GaP nanowires in the zinc-blende structure which allows for a direct comparison of the luminescence properties. Details of structural and optical characterization on wurtzite GaP-based nanowires will be presented.
 A. De, et al., Phys Rev B, 81: 155210, 2010.
 A. Belabbes, et al., Phys Rev B, 86: 075208, 2012.
 C. Yeh, et al., Phys Rev B, 50: 2715, 1994.
 S. Assali, et al., Nano Lett., 13: 1559, 2013.
 L. Gagliano, et al., Nano Lett., 16: 7930, 2016.
 A. Dobrovolsky et al., Nano Lett., 15: 4052, 2015.
 F.Glas, et al. Phys Rev Lett. 99: 146101, 2007.
2:15pm - 2:30pmOral
Electronic Structure and Optical Gain of InNBiAs/InP Pyramidal Quantum Dots
1School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore; 2State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, China
The electronic bandstructure and optical gain of InNxBiyAs1−x−y/InP pyramidal quantum dots (QDs) are investigated using a 16-band k·p model with band anticrossing (BAC) and valence band anticrossing (VBAC) considerations using virtual crystal approximation. The optical gain is calculated taking both homogeneous and inhomogeneous broadenings into consideration. The effective bandgap decreases as we increase the concentration of nitrogen (N) and bismuth (Bi) and with an appropriate choice of N and Bi doping (around 0 – 6%), we can tune the emission wavelength to span within 1.75 µm–3.64 µm, for device applications in infrared technology. The concentration gradient of bandgap is nearly -28 meV per % of Bi and -32 meV per % of N, leveraging which allows us to have precise control over the bandgap. Moreover, the presence of N induces tensile strain, while the presence of Bi induces compressive strain, and they have a nullifying effect allowing us to have near-lattice-matched material suitable for high quality material synthesis. We have also considered the strain profile, which has a profound impact on the electronic structure, specially the valence band of QDs, and can be determined using the composition distribution of wavefunctions. With an increase in QD size, we observe a redshift in the emission energy. The extent of this redshift is more profound in QDs compared to bulk material due to quantum confinement. We have calculated the optical gain spectra with increasing Bi concentration from 0 to 11% and fixed N concentration at 2.9%. The magnitude of transverse magnetic mode gain was found to be much lesser compared to the transverse electric mode gain. The position of the primary gain peak has a redshift with increasing Bi concentration. Conclusively, the presence of N and Bi decrease the band gap of the QD and can realize the 2µm laser.
2:30pm - 2:45pmOral
Enabling III-nitride Photonic Integrated Circuit Based on Semipolar InGaN/GaN Quantum Well Laser Diodes
1Photonics Laboratory, King Abdullah University of Science and Technology (KAUST), Saudi Arabia; 2Materials Department, University of California Santa Barbara (UCSB), United States; 3King Abdulaziz City for Science and Technology (KACST), Saudi Arabia
III-nitride optoelectronic devices are essential for light generation, transmission, modulation and detection in the visible regime. Particularly, the InGaN/GaN quantum well (QW) based laser diodes (LDs) has recently shown advantages as a viable high-power light source. To date, smart lighting and visible-light communication (VLC) functionalities have been demonstrated based on discrete devices, such as InGaN-based LDs, transverse-transmission modulators, and photodetectors. In this presentation, we propose, design, fabricate and characterize the integration of III-nitride photonic components, including the LD, waveguide modulator, amplifier, and photodetector, towards the realization of III-nitride photonic integrated circuit (PIC). Such on-chip integration offers the advantages of small-footprint, high-speed, and low power consumption, which is not feasible using QWs grown on conventional polar, c-plane GaN substrate. This is due to a large Stokes shift between the emission and absorption response, originating from the large polarization field. In other words, the integrated photonic devices are not efficient due to a considerable small overlap between the emission and absorption peaks. Our work demonstrates the utilization of multi-section InGaN-based LDs on semipolar GaN substrate for efficient GaN-based photonic integration. A blue-emitting integrated waveguide modulator-laser diode (IWM-LD) exhibits a high modulation efficiency of 2.68 dB/V, which is more than double of the value in the c-plane counterpart. An integrated short-wavelength semiconductor optical amplifier with the laser diode at ~404 nm is demonstrated with a large gain of 5.32 dB at 6 V. A high-performance InGaN-based waveguide photodetector integrated LD sharing the single active region is presented with a responsivity of 0.051 A/W at 405 nm and a large modulation bandwidth of 230 MHz. The findings are significant in developing the platform technology to enable III-nitride PIC for smart lighting and display, VLC, optical switching, clocking and optical interconnect.
2:45pm - 3:00pmOral
White–Green Emitting Behavior of Core/ Shell (CdSe/ZnS) QDs for LED Applications
Department of Nanoscience and Technology, Alagappa University, India
In the present work, CdSe/ZnS core-shell quantum dots (QDs) were synthesized via chemical route using bio-conjugated organic amino acid (L-Cysteine). The high intensity XRD result (002) plane the right panel of CdSe/ZnS QDs is identical with the c-axis of the wurtzite structure. The diameter of the resulting QDs was about 3 nm with uniform size distribution. The synthesized QDs exhibited an absorption and emission peak at 515 and 525 nm respectively, at room temperature. QDs with emission in the spectral range of 516-535 nm are special for their application in green LEDs and white-light generation.