Semiconductor Medium Research Articles

Reaction-diffusion optoelectronics based on dispersed semiconductors

Since many dispersed semiconductors are capable of light energy conversion and possess photocatalytic and luminescent properties, and any discreet light-sensitive medium can be applied for the positional-sensitive light flux registration (similar to pixels and voxels in semiconductor-based image recording), the use of chemically active dispersed semiconductors allows to perform a direct signal / image registration based on light-sensitive reaction-diffusion redox systems without conventional CCD / CMOS devices. The image capturing in this case will correspond to the formation of the metastable dissipative structures in the active medium, with their morphological properties determined by the flux gradient and provided by the corresponding dispersed semiconductor medium sensitivity.

Random lasing in disordered semiconductor medium with four-level two-electron atomic system

A four-level two-electron model, in which transitions between the energy levels are governed by coupled rate equations and the Pauli Exclusion Principle (PEP), is used in FDTD method for simulation random lasing of disordered semiconductor gain medium. For comparison, the gain threshold behavior of optically pumped random lasing is investigated in three atomic systems: a four-level two-electron atomic system with PEP, a four-level two-electron atomic system without PEP and a four-level one-electron atomic system without PEP. Computed results show that the first excited mode with PEP is different from that without PEP. Further analysis demonstrates that thresholds in four-level two-electron atomic system with PEP are higher than that without PEP about an order of magnitude.

Fabrication and characterization of Er+3 doped SiO2/SnO2 glass-ceramic thin films for planar waveguide applications

Glass-ceramics are a kind of two-phase materials constituted by nanocrystals embedded in a glass matrix and the respective volume fractions of crystalline and amorphous phase determine the properties of the glass-ceramics. Among these properties transparency is crucial in particular when confined structures, such as, dielectric optical waveguides, are considered. Moreover, the segregation of dopant rare-earth ions, like erbium, in low phonon energy crystalline medium makes these structures more promising in the development of waveguide amplifiers. Here we are proposing a new class of low phonon energy tin oxide semiconductor medium doped silicate based planar waveguides. Er3+ doped (100-x) SiO2-xSnO2 (x= 10, 20, 25 and 30mol%), glass-ceramic planar waveguide thin films were fabricated by a simple sol-gel processing and dip coating technique. XRD and HRTEM studies indicates the glass-ceramic phase of the film and the dispersion of ~4nm diameter of tin oxide nanocrystals in the amorphous phase of silica. The spectroscopic assessment indicates the distribution of the dopant erbium ions in the crystalline medium of tin oxide. The observed low losses, 0.5±0.2 dB/cm, at 1.54 μm communication wavelength makes them a quite promising material for the development of high gain integrated optical amplifiers.

Ultrafast Degenerate Transient Lens Spectroscopy in Semiconductor Nanosctructures

We report the non-resonant excitation and probing of the nonlinear refractive index change in bulk semiconductors and semiconductor quantum dots through degenerate transient lens spectroscopy. The signal oscillates at the center laser field frequency, and the envelope of the former in quantum dots is distinctly different from the one in bulk sample. We discuss the applicability of this technique for polarization state probing in semiconductor media with femtosecond temporal resolution.

Resistance switching in rejuvenated NaNbO3:Mn crystals

In this paper, the resistance switching effect has been studied in NaNbO3:Mn crystals. Samples were rejuvenated in ambient air, below and above antiferroelectric phase transition. Dielectric spectroscopy has exhibited weak dispersion. The influence of annealing on the electronic structure has been determined with the use of X-ray photoelectron spectroscopy. Na2s, Nb3d, O1s, and Mn2p lines of the aged as-grown crystal and the rejuvenated samples spectra have been analyzed. Nb4+ states observed in the samples point to the presence of oxygen vacancies in the surface layer. Na ions migrate toward the surface due to rejuvenation. Switching from an insulator high-resistance state to a semiconductor medium resistance and finally to a metallic-type low-resistance state has been observed. The results are discussed within the framework of the extended defects model. We propose that the aliovalent Mn2+ dopant ions stabilize the oxygen vacancies and enable the resistive switching.

Large and robust electrical spin injection into GaAs at zero magnetic field using an ultrathin CoFeB/MgO injector

Binary information encoded within the spin of carriers can be transferred into corresponding right- or left-handed circularly polarized photons emitted from an active semiconductor medium via carrier-photon angular momentum conversion. In order to attain maximized spin injection at out-of-plane magnetic remanence, a number of material systems have been explored as possible solid-state spin injectors. However, the circular polarization $({P}_{\mathrm{C}})$ of emitted light was still limited at 3--4% at remanence. Here, we demonstrate a sizable electroluminescence circular polarization from a III-V-based spin light-emitting diode at zero magnetic field with a perpendicular spin injector consisting of an ultrathin CoFeB ferromagnetic layer (1.2 nm) grown on a MgO tunnel barrier (2.5 nm). The maximum value of ${P}_{\mathrm{C}}$ measured at zero field is as large as 20% at 25 K and still 8% at 300 K. These types of ultrathin perpendicular spin injectors are of great interest (i) to realize the electrical switching of the magnetization of the injector layer owing to the advanced spin-transfer torque properties of the CoFeB layer and (ii) to be directly embedded in optical cavities for spin lasers due to their very low optical absorption loss.

Nonlinear scattering by magnetically biased semiconductor layer

The nonlinear interaction of waves in the semiconductor slab illuminated by the plane waves of two tones or two Gaussian pulses with different central frequencies and lengths is examined in the self-consistent problem formulation, taking into account the nonlinear dynamics of carriers. The three-wave mixing technique is applied to study the nonlinear processes. It has been shown that the nonlinearity in passive weakly nonlinear semiconductor medium has the resistive nature associated with the dynamics of carriers. It has been shown that the nonlinear response of the magnetoactive semiconductor layer is strongly enhanced by the magnetic bias and the combinations of layer physical and geometrical parameters.

Delayed feedback control of self-mobile cavity solitons

Control of the motion of cavity solitons is one the central problems in nonlinear optical pattern formation. We report on the impact of the phase of the time-delayed optical feedback and carrier lifetime on the self-mobility of localized structures of light in broad area semiconductor cavities. We show both analytically and numerically that the feedback phase strongly affects the drift instability threshold as well as the velocity of cavity soliton motion above this threshold. In addition we demonstrate that non-instantaneous carrier response in the semiconductor medium is responsible for the increase in critical feedback rate corresponding to the drift instability.

Phase Noise of the Radio Frequency (RF) Beatnote Generated by a Dual-Frequency VECSEL

We analyze, both theoretically and experimentally, the phase noise of the radio frequency (RF) beatnote generated by optical mixing of two orthogonally polarized modes in an optically pumped dual-frequency Vertical External Cavity Surface Emitting Laser (VECSEL). The characteristics of the RF phase noise within the frequency range of 10 kHz - 50 MHz are investigated for three different nonlinear coupling strengths between the two lasing modes. In the theoretical model, we consider two different physical mechanisms responsible for the RF phase noise. In the low frequency domain (typically below 500 kHz), the dominant contribution to the RF phase noise is shown to come from the thermal fluctuations of the semicondutor active medium induced by pump intensity fluctuations. However, in the higher frequency domain (typically above 500 kHz), the main source of RF phase noise is shown to be the pump intensity fluctuations which are transfered to the intensity noises of the two lasing modes and then to the phase noise via the large Henry factor of the semiconductor gain medium. For this latter mechanism, the nonlinear coupling strength between the two lasing modes is shown to play an important role in the value of the RF phase noise. All experimental results are shown to be in good agreement with theory.

Surface plasmon dispersion in metal hole array lasers

We experimentally study surface plasmon lasing in a series of metal hole arrays on a gold-semiconductor interface. The sub-wavelength holes are arranged in square arrays of which we systematically vary the lattice constant and hole size. The semiconductor medium is optically pumped and operates at telecom wavelengths (λ ~ 1.5 μm). For all 9 studied arrays, we observe surface plasmon (SP) lasing close to normal incidence, where different lasers operate in different plasmonic bands and at different wavelengths. Angle- and frequency-resolved measurements of the spontaneous emission visualizes these bands over the relevant (ω, k||) range. The observed bands are accurately described by a simple coupled-wave model, which enables us to quantify the backwards and right-angle scattering of SPs at the holes in the metal film.

Efficient electro-optic semiconductor medium based on type-II heterostructures

An electro-optic medium based on the type-II semiconductor superlattice is proposed. Electrooptic modulation of the intensity of optical reflectance of the electro-optic medium integrated into a vertical Fabry-Perot cavity is studied by the optical-reflectance-spectroscopy method. The experimental data are approximated using an oscillator model of exciton absorption. The efficiency of the electro-optic medium in the case of detuning from the absorption peak by 50 meV in electric fields of 0–50 kV/cm is 10−9 m/V at a medium filling factor of 100%.

Frequency stability of a 10 GHz optical frequency comb from a semiconductor-based mode-locked laser with an intracavity 10,000 finesse etalon

An optical frequency comb is constructed using a semiconductor gain medium with a fiber-coupled external cavity and stabilized to an intracavity 10,000 finesse etalon, which is temperature stabilized and held in a vacuum chamber at 10(-6) Torr. Optical frequency stability measurements show that the comb has a reduced sensitivity to environmental fluctuations. An upper limit on the optical frequency variation of 100 kHz over >12 min of continuous operation is measured using a real-time spectrum analyzer. This measurement is limited by the linewidth of the reference source, and further measurements with a frequency counter show a fractional deviation of 2×10(-11) at 50 ms. Furthermore, out-of-band ASE rejection is shown to be >36 dB, a tenfold improvement over that of a laser with a 1000 finesse FPE.

Design and fabrication of an electrical injection metallic bowtie plasmonic structure integrated with semiconductor gain medium

We propose and demonstrate a design and fabrication of an electrical injection metallic bowtie (MB) structure integrated with semiconductor gain medium. Our integrated bowtie-semiconductor structure takes the advantage of selective wet chemical etching of InGaAsP, allowing the formation of a bowtie shaped gain structure by a single step etching. The subsequent metal deposition allows the nature integration of gain medium between two bowtie tips. Electroluminescence was observed from fabricated structures at 78 K. Such gain embedded MB structures open the potential for large scale fabrication of plasmonic structures for various applications such as nanolasers and plasmonic generation under electrical injection.

Design of Ultra-Small Metallic-Semiconductor Nano-Ring Cavity Lasers

We present design and analysis of metallic-semiconductor nanoring laser lasing at around 1450 nm wavelength, utilizing a body-of-revolution finite-difference-time-domain (BOR-FDTD) simulation incorporated with a semiclassical multilevel model for semiconductor gain medium and the Drude-Lorentz model for metal, which is developed for efficient simulation of disk/ring plasmonic laser. As compared to other literature, our nanoring laser works in radial mode with resonance cycle, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> =1, which could facilitate potential in-plane out-coupling, and is wafer bonded onto Si platform for potential electronic-photonic integration. The total footprint, the physical device volume, and the effective mode volume of the nanolaser are only about 0.038 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , 1.1(λ/2 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> ) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , and 0.001(λ/2 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> ) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , respectively, where <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> is the average refractive index of the gain medium. To the best of our knowledge, our nanolaser is the smallest reported to date.

Dynamical regimes of a multistripe laser array with external off-axis feedback

We theoretically study the dynamics of a multistripe laser array with an external cavity formed by either one or two off-axis feedback mirrors, which allow us to select a single lateral supermode with transversely modulated intensity distribution. We derive and analyze a reduced model of such an array based on a set of delay differential equations, taking into account transverse carrier grating in the semiconductor medium. With the help of the bifurcation analysis of the reduced model, we show the existence of single and multimode instabilities leading to periodic and irregular pulsations of the output intensity. In particular, we observe a multimode instability leading to a periodic regime with antiphase oscillating intensities of the two counter-propagating waves in the external cavity. This is in agreement with the result obtained earlier with the help of a 2+1 dimensional traveling wave model.

Terahertz frequency upconversion via relativistic Doppler reflection from a photoinduced plasma front in a solid-state medium

We propose and simulate the relativistic Doppler reflection of terahertz (THz) radiation normally incident on a plasma front in a semiconductor medium, resulting in a significant frequency upshift for the reflected radiation. The plasma front is generated by linear interband excitation of the semiconductor by a counterpropagating femtosecond optical pulse. High-resistivity silicon is identified as an ideal medium for experiments, as it possesses a desirable optical penetration depth, upshift factor, and low THz absorption and dispersion. The depletion of the optical pump pulse results in a spatiotemporal plasma profile, which leads to results that go beyond the existing analytic theory. We employ one-dimensional finite-difference time-domain simulations to predict the reflected THz pulses vs a range of realistic experimental parameters. The results indicate that a significant frequency upshift can be expected for both conventional and ultrabroadband THz pulses, and that this technique may be suitable to provide higher-bandwidth THz radiation extending into the midinfrared.

Linewidth enhancement in spasers and plasmonic nanolasers

The concept of spaser as the coherent near-field generator and nanolaser based on nanoscale plasmonic resonators has been successfully demonstrated in number of experiments. Here we have developed the theoretical framework for the basic linewidth description of these active plasmonic structures and, in particular, linewidth enhancement - additional line broadening due to the resonator noise. In order to achieve this, we have introduced explicitly the time dependence in the quasistatic description of localized surface plasmon resonances via inclusion of the dispersion of a spectral parameter defining the resonant frequency. Linewidth enhancement factor was estimated for semiconductor gain medium and was found to be of order of 3 to 6, strongly depending on carrier density in the active layer, and resulting in more than order of magnitude broader linewidth compared to that, predicted by the Schawlow-Townes theory.

InGaAs Quantum Dots on Cross‐Hatch Patterns as a Host for Diluted Magnetic Semiconductor Medium

Storage density on magnetic medium is increasing at an exponential rate. The magnetic region that stores one bit of information is correspondingly decreasing in size and will ultimately reach quantum dimensions. Magnetic quantum dots (QDs) can be grown using semiconductor as a host and magnetic constituents added to give them magnetic properties. Our results show how molecular beam epitaxy and, particularly, lattice‐mismatched heteroepitaxy can be used to form laterally aligned, high‐density semiconducting host in a single growth run without any use of lithography or etching. Representative results of how semiconductor QD hosts arrange themselves on various stripes and cross‐hatch patterns are reported.

A Numerical Simulation of Nanodisk Semiconductor-Plasmonic Laser Using BOR-FDTD With a Multilevel Gain Medium Model

A temporal and spatial simulation and design of nanoplasmonic laser based on a semiconductor nanodisk is presented in this paper. A body-of-revolution finite-difference-time-domain (BOR-FDTD) simulation incorporated with a semiclassical multilevel model for the semiconductor gain medium and Drude-Lorentz model for the metal is developed for an efficient simulation of disk/ring plasmonic laser. A nanodisk semiconductor-plasmonic laser with a radius of 35 nm is designed, and the spatial and temporal lasing performance is demonstrated numerically.

SESAM‐free mode‐locked semiconductor disk laser

AbstractExperimental demonstration of semiconductor saturable absorber‐free mode‐locked optically pumped semiconductor disk laser is presented. The origin of pulsed operation is attributed to the intensity dependent Kerr lens effect arising in the semiconductor gain medium. Achieved results represent a novel method to mode‐lock this type of laser opening new application opportunities. The laser worked stably in both hard and soft aperture configurations. No semiconductor saturable absorber was used in the laser cavity and the operation was self‐starting. The laser was mode‐locked at 210 MHz repetition rate with 1.5 W average output power and 930 fs pulse width at 985 nm. A record high 6.8 kW peak power was achieved. Measured data is presented along with a discussion of the Kerr lens effect in the cavity.