Contact printing of colloidal nanocrystal thin films for hybrid organic/quantum dot optoelectronic devices

Novel thin film optoelectronic devices containing both inorganic colloidal semiconductor quantum dots (QDs) and organic semiconductor thin films have been widely investigated in recent years for a variety of applications. Here, we review one of the most versatile and successful methods developed to integrate these two dissimilar material classes into a functional multilayered device: contact printing of colloidal QD films. Experimental details regarding the contact printing process are outlined, and the key advantages of this QD deposition method over other commonly encountered techniques are discussed. The use of tapping mode atomic force microscopy (AFM) to effectively characterize QD film morphology both on an elastomeric stamp (before contact printing) and as-transferred to the organic semiconductor receiving film (after contact printing) is also described. Finally, we offer suggestions for future efforts directed toward the goal of rapid, continuous QD deposition over larger substrates for the advancement of hybrid optoelectronic thin film devices

Monolithic quantum-dot distributed feedback laser array on silicon

Electrically-pumped lasers directly grown on silicon are key devices interfacing silicon microelectronics and photonics. We report here, for the first time, an electrically-pumped, room-temperature, continuous-wave (CW) and single-mode distributed feedback (DFB) laser array fabricated in InAs/GaAs quantum-dot (QD) gain material epitaxially grown on silicon. CW threshold currents as low as 12 mA and single-mode side mode suppression ratios (SMSRs) as high as 50 dB have been achieved from individual devices in the array. The laser array, compatible with state-of-the-art coarse wavelength division multiplexing (CWDM) systems, has a well-aligned channel spacing of 20 0.2 nm and exhibits a record wavelength coverage range of 100 nm, the full span of the O-band. These results indicate that, for the first time, the performance of lasers epitaxially grown on silicon is elevated to a point approaching real-world CWDM applications, demonstrating the great potential of this technology

III-V Quantum Dot Lasers Epitaxially Grown on Si

Monolithic integration of semiconductor lasers on silicon platform is the ultimate solution for creating complex optoelectronic circuits, which is the key to chip-to-chip and system-to-system communications. The direct epitaxial integration of III-V semiconductor materials on Si or Ge is one of the most promising approaches for the fabrication of electrically pumped light sources on a Si platform, promising low-cost, high-yield and large-scale deployment of silicon photonics [1], [2]. However, monolithic integration technique faces significant challenges because of the large material dissimilarity between III-V and Group IV materials, such as lattice mismatch, thermal expansion coefficient differences, and polar versus nonpolar surfaces [2], [3]. These differences tend to produce various types of defects, such as, antiphase boundaries (APBs), threading dislocations (TDs), and microcracks, which all generate nonradiative recombination centers and dramatically undermine the promise of III-V materials. Recently, quantum dots (QDs) structure is becoming widely used in active layer in semiconductor lasers due to their advantages of low threshold current density and temperature insensitive operation [4], [5]. Also, QD structures have attracted increasing attention for the monolithic III-V/Si integration due to their enhanced tolerance to defects and special capability of filtering the APBs and threading dislocations [6], [7]. In this paper, we review our recent progress made in the direct growth of III-V QD lasers on Si substrates

Optically pumped intersublevel midinfrared lasers based on InAs-GaAs quantum dots

We propose an optically pumped laser based on intersublevel transitions in InAs-GaAs pyramidal self-Assembled quantum dots. A theoretical rate equations model of the laser is given in order to predict the dependence of the gain on pumping flux and temperature. The energy levels and wave functions were calculated using the 8-band k . p method where the symmetry of the pyramid was exploited to reduce the computational complexity. Carrier dynamics in the laser were modeled by taking both electron-longitudinal optical phonon and electron-longitudinal acoustic phonon interactions into account. The proposed laser emits at 14.6 μm with a gain of g ≈ 570 cm(-1) at the pumping flux Φ= 10(24) cm(-2) s(-1) and a temperature of T = 77 K. By varying the size of the investigated dots, laser emission in the spectral range 13-21 μm is predicted. In comparison to optically pumped lasers based on quantum wells, an advantage of the proposed type of laser is a lower pumping flux, due to the longer carrier lifetime in quantum dots, and also that both surface and edge emission are possible. The appropriate waveguide and cavity designs are presented, and by comparing the calculated values of the gain with the estimated losses, lasing is predicted even at room temperature for all the quantum dots investigated

Carrier escape from ground state and non-zero resonance frequency at low bias powers for semiconductor quantum-dot lasers

International audienceThe three-dimensional confinement of electrons and holes in the semiconductor quantum dot (QD) structure profoundly changes its density of states compared to the bulk semiconductor or the thin-film quantum well (QW) structure. The aim of this paper is to theoretically investigate the microwave properties of InAs/InP(311B) QD lasers. A new expression of the modulation transfer function is derived for the analysis of QD laser modulation properties based on a set of four rate equations. Analytical calculations point out that carrier escape from ground state (GS) to excited state (ES) induces a non-zero resonance frequency at low bias powers. Calculations also show that the carrier escape leads to a larger damping factor offset as compared to conventional QW lasers. These results are of prime importance for a better understanding of the carrier dynamics in QD lasers as well as for further optimization of low cost sources for optical telecommunications

Kinetics of epitaxial formation of nanostructures by Frank-van der Merwe, Volmer-Weber and Stranski-Krastanow growth modes

Nowadays, two-dimensional crystals (2D materials) and structures with quantum dots (0D materials) are considere

Low-noise 1.3 μm InAs/GaAs quantum dot laser monolithically grown on silicon

We report low-noise, high-performance single transverse mode 1.3 μm InAs/GaAs quantum dot lasers monolithically grown on silicon (Si) using molecular beam epitaxy. The fabricated narrow-ridge-waveguide Fabry–Perot (FP) lasers have achieved a room-temperature continuous-wave (CW) threshold current of 12.5 mA and high CW temperature tolerance up to 90°C. An ultra-low relative intensity noise of less than −150  dB/Hz is measured in the 4–16 GHz range. Using this low-noise Si-based laser, we then demonstrate 25.6 Gb/s data transmission over 13.5 km SMF-28. These low-cost FP laser devices are promising candidates to provide cost-effective solutions for use in uncooled Si photonics transmitters in inter/hyper data centers and metropolitan data links

Quantum dots on the InAs(110) cleavage surface created by atom manipulation

Cryogenic scanning tunneling microscopy was employed in combination with density-functional theory calculations to explore quantum dots made of In adatoms on the InAs(110) surface. Each adatom adsorbs at a surface site coordinated by one cation and two anions, and transfers one electron to the substrate, creating an attractive quantum well for electrons in surface states. We used the scanning-probe tip to assemble the positively charged adatoms into precisely defined quantum dots exhibiting a bound state roughly 0.1 eV below the Fermi level at an intrinsic linewidth of only ~4 meV, as revealed by scanning tunneling spectroscopy. For quantum-dot dimers, we observed the emergence of a bonding and an antibonding state with even and odd wave-function character, respectively, demonstrating the capability to engineer quasi-molecular electronic states. InAs(110) constitutes a promising platform in this respect because highly perfect surfaces can be readily prepared by cleavage and charged adatoms can be generated in-situ by the scanning-probe tip.Comment: 13 pages of referenced main text including 5 embedded figures plus legends; 4 pages of Supplementary Material including 3 figures plus legend

АНАЛИЗ ЭЛЕКТРОННОЙ СТРУКТУРЫ ЭЛЕКТРИЧЕСКИ ИНДУЦИРОВАННОЙ КВАНТОВОЙ ТОЧКИ ВО ВНЕШНЕМ МАГНИТНОМ ПОЛЕ

 Numerical modeling of the electronic structure of a quantum dot, induced by an electric field of a nanosized disc-shaped gate, is carried out in the presence of external magnetic field. The dependences of an electronic energy spectrum on electric and magnetic fields are calculated using the finite element method. It has been found that a series of anti-crossing points for electronic levels takes place at relatively small magnetic fields. The existence of groups of close-energy levels (electronic shells) has been found. It has been shown that despite the essential distinction of the gate potential from the parabolic one, a model of a near-surface anisotropic harmonic oscillator can be effectively used for a qualitative description of the electronic structure of the electrically induced quantum dot. With the use of this model, the evolution of energy spectrum and wave function structure with magnetic and electric fields is described. In particular, the anisotropic oscillator model allows to predict anti-crossing points of electronic levels in external fields, as well as quasi-degeneracy of states having different values of the angular momentum projection.  Проведено численное моделирование электронной структуры квантовой точки, индуцированной электрическим полем наноразмерного дискообразного затвора и находящейся во внешнем магнитном поле. С помощью метода конечных элементов рассчитаны зависимости энергетического спектра электрона от величины магнитного поля и потенциала на затворе. Обнаружено наличие последовательности точек квазипересечения электронных уровней при относительно слабых магнитных полях, а также существование групп близких уровней энергии (электронных оболочек). Показано, что, несмотря на существенное отличие потенциала затвора от параболического потенциала, для качественного описания электронной структуры электрически индуцированной квантовой точки возможно использование модели приповерхностного анизотропного гармонического осциллятора. На основании этой модели описаны закономерности эволюции структуры волновых функций при изменении потенциала затвора и магнитного поля. В частности, модель анизотропного осциллятора позволяет предсказать появление точек квазипересечения электронных уровней при изменении внешних полей, а также квазивырождение состояний с различными значениями проекции орбитального момента импульса. 

Open Circuit Voltage Recovery in Quantum Dot Solar Cells: a Numerical Study on the Impact of Wetting Layer and Doping

The authors present a numerical study on the influence of wetting layer states and doping on the photovoltage loss of InAs/GaAs quantum dot solar cells. Quantum-mechanical simulations are used to analyse how the reduction of wetting layer by Al(Ga)As overgrowth changes the quantum dot electronic states. Device-level simulations allow to correlate such changes with the achievable open circuit voltage. Almost full open circuit voltage recovery is predicted by combining wetting layer reduction, to realise thermal decoupling of barrier and quantum dot confined states, and doping to suppress radiative recombination through the quantum dot confined states