GaAs-based Structure Research Articles

Numerical Investigation of G–V Measurements of metal – A Nitride GaAs junction

In this study, a Schottky diode consisting of Au/GaN/GaAs was fabricated using a radiofrequency nitrogen plasma source. The voltage-conductance characteristics (G/ω-V) of this diode structure were investigated at room temperature. To interpret the changes in the electrical properties of the nitrided GaAs-based Schottky structure, we developed a simulation program. This program employs a numerical model to calculate the G-V characteristics, allowing us to validate the experimental measurements conducted on the Schottky diodes. The geometric model used in our simulation considers not only the GaN layer formed between the metal and GaAs substrate but also the density and distribution of trapped states within the band gap. The program utilizes the numerical resolution of the Poisson and continuity equations to calculate the electrostatic potential and the concentrations of both n and p mobile carriers. These parameters are then used to determine the electric charge, current, capacitance, and conductance. The simulation results were subsequently compared to the experimental measurements to ensure their accuracy.

Metamorphic Buffer Layer Platform for 1550 nm Single-Photon Sources Grown by MBE on (100) GaAs Substrate.

We demonstrate single-photon emission with a low probability of multiphoton events of 5% in the C-band of telecommunication spectral range of standard silica fibers from molecular beam epitaxy grown (100)-GaAs-based structure with InAs quantum dots (QDs) on a metamorphic buffer layer. For this purpose, we propose and implement graded In content digitally alloyed InGaAs metamorphic buffer layer with maximal In content of 42% and GaAs/AlAs distributed Bragg reflector underneath to enhance the extraction efficiency of QD emission. The fundamental limit of the emission rate for the investigated structures is 0.5 GHz based on an emission lifetime of 1.95 ns determined from time-resolved photoluminescence. We prove the relevance of a proposed technology platform for the realization of non-classical light sources in the context of fiber-based quantum communication applications.

The investigation of InGaAs quantum dot growth peculiarities for GaAs intermediate band solar cells

In this work the growth peculiarities of InGaAs quantum dots (QDs) on GaAs surface have been investigated by metal-organic vapor-phase epitaxy (MOVPE). The influence of the main structural parameters, such as the amount of deposited InGaAs material and the thickness of the GaAs cap layer, on the optical properties of QDs has been considered. For these parameters the optimal values at which achieved the best photoluminescence intensity of QDs embedded into the matrix of the GaAs-based light-emitting structure have been established. The possibility of using several layers of QDs with the preservation of the optical properties of the investigated structures has been demonstrated. The design of solar cell (SC) based on GaAs with QD arrays in the active area has been proposed. It was shown that 20 layers of QDs embedded into the proposed SC structure contribute to the photogenerated current up to 0.97 mA/cm2 for AM0 spectra and up to 0.77 mA/cm2 for AM1.5D spectra, while maintaining the high quality of the p-n junction.

Effect of Dislocation-related Deep Levels in Heteroepitaxial InGaAs/GaAs and GaAsSb/GaAs p–i–n Structures on the Relaxation time of Nonequilibrium Carriers

The results of an experimental study of the capacitance–voltage (C–V) characteristics and deep-level transient spectroscopy (DLTS) spectra of p+–p0–i–n0 homostructures based on undoped dislocationfree GaAs layers and InGaAs/GaAs and GaAsSb/GaAs heterostructures with homogeneous networks of misfit dislocations, all grown by liquid-phase epitaxy (LPE), are presented. Deep-level acceptor defects identified as HL2 and HL5 are found in the epitaxial p0 and n0 layers of the GaAs-based structure. The electron and hole dislocation-related deep levels, designated as, respectively, ED1 and HD3, are detected in InGaAs/GaAs and GaAsSb/GaAs heterostructures. The following hole trap parameters: thermal activation energies (E t ), capture cross sections (σ p ), and concentrations (N t ) are calculated from the Arrhenius dependences to be E t = 845 meV, σ p = 1.33 × 10–12 cm2, N t = 3.80 × 1014 cm–3 for InGaAs/GaAs and E t = 848 meV, σ p = 2.73 × 10–12 cm2, N t = 2.40 × 1014 cm–3 for GaAsSb/GaAs heterostructures. The concentration relaxation times of nonequilibrium carriers are estimated for the case in which dislocation-related deep acceptor traps are involved in this process. These are 2 × 10–10 s and 1.5 × 10–10 s for, respectively, the InGaAs/GaAs and GaAsSb/GaAs heterostructures and 1.6 × 10–6 s for the GaAs homostructures.

Влияние глубоких уровней дислокаций в гетероэпитаксиальных InGaAs/GaAs и GaAsSb/GaAs p-i-n-структурах на время релаксации неравновесных носителей

AbstractThe results of an experimental study of the capacitance–voltage ( C – V ) characteristics and deep-level transient spectroscopy (DLTS) spectra of p ^+– p ^0– i – n ^0 homostructures based on undoped dislocationfree GaAs layers and InGaAs/GaAs and GaAsSb/GaAs heterostructures with homogeneous networks of misfit dislocations, all grown by liquid-phase epitaxy (LPE), are presented. Deep-level acceptor defects identified as HL 2 and HL 5 are found in the epitaxial p ^0 and n ^0 layers of the GaAs-based structure. The electron and hole dislocation-related deep levels, designated as, respectively, ED 1 and HD 3, are detected in InGaAs/GaAs and GaAsSb/GaAs heterostructures. The following hole trap parameters: thermal activation energies ( E _ t ), capture cross sections (σ_ p ), and concentrations ( N _ t ) are calculated from the Arrhenius dependences to be E _ t = 845 meV, σ _ p = 1.33 × 10^–12 cm^2, N _ t = 3.80 × 10^14 cm^–3 for InGaAs/GaAs and E _ t = 848 meV, σ _ p = 2.73 × 10^–12 cm^2, N _ t = 2.40 × 10^14 cm^–3 for GaAsSb/GaAs heterostructures. The concentration relaxation times of nonequilibrium carriers are estimated for the case in which dislocation-related deep acceptor traps are involved in this process. These are 2 × 10^–10 s and 1.5 × 10^–10 s for, respectively, the InGaAs/GaAs and GaAsSb/GaAs heterostructures and 1.6 × 10^–6 s for the GaAs homostructures.

Analysis of dark currents and deep level traps in InP- and GaAs-based In0.83Ga0.17As photodetectors

InP- and GaAs-based metamorphic In0.83Ga0.17As photodetectors were grown and investigated. Compared to InP-based photodetector, the dark current of GaAs-based photodetector at room temperature increased 2–3 times but still comparable, whereas at 77K the dark current increased 2–3 orders. The deep-level transient spectroscopy results reveal that a deep level trap state exists in the GaAs-based photodetector structure. The higher dark current in GaAs-based photodetector at low temperature was mainly ascribed to a deep level trap induced tunneling current. The deep trap centers can also induce non-radiative recombination with smaller thermal active energy in the GaAs-based photodetector structure.

Concept and numerical simulations of a widely tunable GaAs‐based sampled‐grating diode laser emitting at 976 nm

Tunable diode lasers are essential components in various optical systems. The authors present a concept and simulations of a four-section, widely tunable GaAs-based sampled-grating (SG) distributed-Bragg reflector (DBR) laser emitting at 976 nm. This work includes the design approach of the SG reflectors and the simulation of the behaviour of the modes in the active cavity during the wavelength tuning process. Parameters such as the lasing wavelength, threshold current and the gain of the lasing and of the adjacent side modes during the tuning are presented. The numerical results presented suggest a tunability of at least 17 nm, with a threshold current change of only 2.5 mA and single-mode operation over the entire tuning range, without the need of simultaneous adjustments of the phase section. Finally, the authors present early experimental results of a developed GaAs-based vertical structure, providing a high coupling coefficient of $\kappa = 240 \, \hbox{c}\hbox{m}^{ - 1}$κ=240 cm-1, thus suitable for implementation of an SG-DBR laser design.

Graphene-GaAs-graphene stacked layers for the improvement of the transmission at the wavelength of 1.55 μm

Transmission filter operating at the wavelength of 1.55 μm and based on stacked graphene-GaAs-graphene layers separated by air gaps is presented. By using the transfer matrix method (TMM), we show that the addition of a graphene layer at each interface of a GaAs-based stratified structure, which initially exhibit only 30% transmission at 1.55 μm, allows the active control of the transmission by the adjustment of the graphene chemical potential. Transmission of almost 100% at the wavelength of 1.55 μm is achieved after addition of graphene layers. These results show the potential role of stacked graphene-GaAs-graphene layers in the development of new optical active communications devices.

Contribution of a single quantum dots layer in intermediate band solar cells: A capacitance analysis

Theoretical model and numerical analysis of charge accumulation within a single GaSb quantum dots layer embedded in GaAs-based Schottky diode is performed. We hereby give an analytical calculation of the capacitance–voltage (C–V) characteristic of GaAs-based Schottky barrier structure incorporating GaSb self-assembled quantum dots layer. The Schottky barrier is derived in different bias voltage region based on solving analytically Poisson׳s equation, including the effects of the dots size dispersion and the Fermi statistics of the holes in the quantum dots. The numerical simulation of capacitance–voltage curves exhibits a plateau that is caused by the high carrier concentration and the saturation of the quantum dots levels upon the applied voltage. These results are in good agreement with experiments done by Hwang et al.

Single photon emission up to liquid nitrogen temperature from charged excitons confined in GaAs-based epitaxial nanostructures

We demonstrate a non-classical photon emitter at near infrared wavelength based on a single (In,Ga)As/GaAs epitaxially grown columnar quantum dot. Charged exciton complexes have been identified in magneto-photoluminescence. Photon auto-correlation histograms from the recombination of a trion confined in a columnar dot exhibit sub-Poissonian statistics with an antibunching dip yielding g(2)(0) values of 0.28 and 0.46 at temperature of 10 and 80 K, respectively. Our experimental findings allow considering the GaAs-based columnar quantum dot structure as an efficient single photon source operating at above liquid nitrogen temperatures, which in some characteristics can outperform the existing solutions of any material system.

15 W Single Frequency Optically Pumped Semiconductor Laser With Sub-Megahertz Linewidth

We report on a single frequency optically pumped semiconductor laser exhibiting an output power of 15 W in continuous wave operation. The GaAs-based structure presents an emission wavelength of 1020 nm and a tuning range , with a continuous tunability of 9 GHz. The TEM00 output beam exhibits very low transverse phase fluctuations across the entire mode, leading to a beam quality . A free-running laser linewidth of 21 kHz has been deduced from frequency noise measurements for a sampling time of 1 ms and increases to 995 kHz for a sampling time of 1 s.

GaAs-based air-slot photonic crystal nanocavity for optomechanical oscillators.

We theoretically investigate an optomechanical structure consisting of two parallel GaAs membranes with an air-slot type photonic crystal nanocavity. The optical cavity has a quality factor of 4.8 × 106 at 1.52 μm and an extremely small modal volume of 0.015 of a cubic wavelength for the fundamental mode in a vacuum. The localized electric field near the air/dielectric-object boundary provides a large optomechanical coupling factor of ~990 GHz/nm. The fundamental mechanical mode resonance is 95 MHz and a quality factor is 83,800 at room temperature, nearly seven times higher than that for a similar Si-based structure. This high mechanical quality factor of a GaAs-based structure stems from low thermoelastic loss and leads to more effective optical control of nanomechanical oscillators.

Nonlinear localized modes in bandgap microcavities

We study experimentally an electrically pumped GaAs-based bandgap structure based on a vertical cavity surface emitting laser (VCSEL). We demonstrate that a microcavity embedded into this bandgap VCSEL structure supports localized optical modes without any holding beam. We propose a model of surface-structured VCSELs based on a reduced dissipative wave equation for describing electromagnetic modes in such semiconductor cavities and analyze a crossover between linear and nonlinear solitonlike cavity modes.

Switching avalanche S-diodes based on GaAs multilayer structures

Results of studying volt-ampere characteristics of switching avalanche S-diodes are presented. It is shown that, for S-diodes based on structures obtained by diffusing Cr into GaAs, a larger part of the applied reverse-biased voltage drops across a high-resistance π-region but not across the space-charge region. In this case, the sharp increase of the current is caused by the electron injection from the forward-biased contact to the π-layer. In this respect, a new GaAs-based structure doped with Cr and Fe (GaAs:Cr, Fe) is studied. It is shown that, in S-diodes based on (GaAs:Cr, Fe)-structures, the current increase under a reverse bias is caused by avalanche processes in the space-charge area. This leads to producing a negative differential resistance section with subnanosecond switching from the closed to open state. The switching voltages of S-diodes on GaAs:Cr, Fe structures vary from 350 to 650 V, and the switching times do not exceed 0.5 ns.

Pressure effect study on the I–V property of the GaAs-based resonant tunnelling structure by photoluminescence measurement

This paper discusses the I–V property of the GaAs-based resonant tunnelling structure (RTS) under external uniaxial pressure by photoluminescence studies. Compressive pressure parallel to the [110] direction, whose value is determined by Hooke's law, is imposed on the sample by a helix micrometer. With the increase of the applied external uniaxial compressive pressure, the blue shift and splitting of the luminescence peaks were observed, which have some influence on the I–V curve of RTS from the point of view of the energy gap, and the splitting became more apparent with applied pressure. Full width at half maximum broadening could also be observed.

Efficient spin injection into semiconductor from an Fe/GaOx tunnel injector

We examined the electrical injection of spin-polarized electrons into a GaAs-based light-emitting diode structure from a Fe/GaOx tunnel injector whose electron-charge injection efficiency was comparable to that of a conventional Fe/n+-AlGaAs ohmic injector. A high circular polarization of electroluminescence up to 20% was observed at 2 K. The combination of effective spin-and charge-injection efficiencies makes GaOx a promising tunnel barrier for GaAs-based spintronic devices.

Chemical polishing method of GaAs specimens for transmission electron microscopy

A practical method for transmission electron microscopy specimen preparation of GaAs-based materials with quantum dot structures is presented to show that high-quality image observations in high-resolution transmission electron microscopy (HRTEM) can be effectively obtained. Specimens were prepared in plan-view and cross-section using ion milling, followed by two-steps chemical fine polishing with an ammonia solution (NH 4OH) and a dilute H 2SO 4 solution. Measurements of electron energy loss spectroscopy (EELS) and atomic force microscopy (AFM) proved that clean and flat specimens can be obtained without chemical residues. HRTEM images show that the amorphous regions of carbon and GaAs can be significantly reduced to enhance the contrast of lattice images of GaAs-based quantum structure.

1150-nm wavelength InGaAs/GaAs VCSELs incorporating regrown tunnel junctions

Results of the development of all metallorganic vapor-phase epitaxy (MOVPE) GaAs-based vertical cavity surface emitting lasers (VCSELs) with a regrown tunnel junction (TJ) emitting at ∼1150-nm wavelength are presented. A zero-bias-specific resistance of ∼3×10 −4 Ω cm 2 has been obtained for the GaAs-based TJ structure. VCSEL devices incorporating 4–7-μm and 12-μm TJ mesas exhibit an ∼2–3 mA threshold current. Room-temperature lasing spectra are multimode with an output power of 1 and 2 mW, respectively, and thermal roll-over is above 25 mA. A 2×2 VCSEL array of 3-μm aperture elements at 7-μm pitch yielding 0.8 mW room-temperature output power has been realized.

Quantum-dot lasers provide high performance near 1.15 microns

Monomode laser diodes in the wavelength range around 1.15μm are of particular interest for applications such as sensing (of moisture, for example) and for frequency doubling into parts of the spectrum that are currently largely inaccessible. Coherent green and yellow light from frequency-doubled lasers would be very useful for gas sensing and other industrial instrumentation, as well as biomedical and fluorescence applications. An essential prerequisite for efficient frequency conversion, however, is single-frequency laser light, such as could be provided by distributed feedback (DFB) laser diodes. One particular challenge at the range around 1.15μm is to produce a gain medium with high internal efficiency. For broad area lasers, good results have recently been achieved using quantum dots (QDs) or high strained InGaAs quantumwells (QWs).1 In general, devices that use QDs can provide a variety of advantages compared to conventional QW-based devices.2 DFB devices are ideally suited to provide longitudinal and transverse single-mode emission at a precise wavelengthwith an extremely narrow linewidth. They guarantee high output power andmode-hop-free tunability. Our DFB concept shown in Figure 1 is based on an overgrowth-free technology, which can easily be adapted to a variety of independent epitaxial designs. Based on this approach, we are manufacturing DFB laser diodes from 760nm up to 2800nm.3, 4 Device fabrication makes use of a GaAs-based laser structure grown by molecular beam epitaxy with an undoped active region consisting of self-organized InGaAs/GaAs QD layers. The spectral gain properties of this underlying QD active region allow us to make DFB lasers with emission spanning a broad wavelength range. We fabricated a ridge waveguide structure using photolithography and an electron-cyclotron-resonance asFigure 1. Schematic of a laterally-coupled distributed-feedback (DFB) laser with a metal grating structure and an active region incorporating quantum dots (QDs).

Huge positive magnetoresistance of GaAs∕AlGaAs high electron mobility transistor structures at high temperatures

The authors have performed magnetoresistivity measurements ρxx(B) on GaAs∕AlGaAs high electron mobility transistor (HEMT) structures at high temperatures T. These HEMT structures show huge positive magnetoresistance (MR). For B=±6T, the MR values are >1300% and >200% at T=20 and 80K, respectively. Since a GaAs-based HEMT structure is not susceptible to ferromagnetic noise which appears to represent a fundamental challenge to the scalability of magnetic MR devices to ultrahigh area densities, the experimental results pave the way for the integration of scalable nonmagnetic MR devices with the mature HEMT technology using the same material system.