Quasi-classical cyclotron resonance of Dirac fermions in highly doped graphene

Cyclotron resonance in highly doped graphene has been explored using infrared magnetotransmission. Contrary to previous work, which only focused on the magneto-optical properties of graphene in the quantum regime, here we study the quasi-classical response of this system. We show that it has a character of classical cyclotron resonance, with an energy which is linear in the applied magnetic field and with an effective cyclotron mass defined by the position of the Fermi level m = E_F/v_F^2.Comment: 6 pages, 4 figure

Direction-sensitive graphene flow sensor

Graphene flow sensors hold great prospects for applications, but also encounter many difficulties, such as unwanted electrochemical phenomena, low measurable signal and limited dependence on the flow direction. This study proposes a novel approach allowing for the detection of a flow direction-dependent electric signal in aqueous solutions of salts, acids and bases. The key element in the proposed solution is the use of a reference electrode which allows external gating of the graphene structure. Using external gating enables to enhance substantially the amplitude of the flow-generated signal. Simultaneous measurement of the reference electrode current allows us to recover a flow-direction-sensitive component of the flow-induced voltage in graphene. The obtained results are discussed in terms of the Coulomb interaction and other phenomena which can be present at the interface of graphene with the aqueous solution.Comment: 7 pages, 6 figure

Indium rich InGaN solar cells grown by MOCVD

This study focuses on both epitaxial growths of InxGa 1-xN epilayers with graded In content, and the performance of solar cells structures grown on sapphire substrate by using metal organic chemical vapor deposition. The high resolution X-ray and Hall Effect characterization were carried out after epitaxial InGaN solar cell structures growth. The In content of the graded InGaN layer was calculated from the X-ray reciprocal space mapping measurements. Indium contents of the graded InGaN epilayers change from 8.8 to 7.1 % in Sample A, 15.7-7.1 % in Sample B, and 26.6-15.1 % in Sample C. The current voltage measurements of the solar cell devices were carried out after a standard micro fabrication procedure. Sample B exhibits better performance with a short-circuit current density of 6 mA/cm2, open-circuit voltage of 0.25 V, fill factor of 39.13 %, and the best efficiency measured under a standard solar simulator with one-sun air mass 1.5 global light sources (100 mW/cm2) at room temperature for finished devices was 0.66 %. © 2014 Springer Science+Business Media New York

Parallel magnetotransport in multiple quantum well structures

The results of investigations of parallel magnetotransport in AlGaAs/GaAs and InGaAs/InAlAs/InP multiple quantum wells structures (MQW’s) are presented in this paper. The MQW’s were obtained by metalorganic vapour phase epitaxy with different shapes of QW, numbers of QW and levels of doping. The magnetotransport measurements were performed in wide region of temperatures (0.5–300 K) and at high magnetic fields up to 30 T (B is perpendicular and current is parallel to the plane of the QW). Three types of observed effects are analyzed: quantum Hall effect and Shubnikov—de Haas oscillations at low temperatures (0.5–6 K) as well as magnetophonon resonance at higher temperatures (77–300 K)

Terahertz Detection by the Entire Channel of High Electron Mobility Transistors

high electron mobility transistors were used as detectors of THz electromagnetic radiation at liquid helium temperatures. Application of high magnetic fields led to the Shubnikov-de Haas oscillations of the detection signal. Measurements carried out with a simultaneous modulation of the intensity of the incident THz beam and the transistor gate voltage showed that the detection signal is determined by the electron plasma both in the gated and ungated parts of the transistor channel. This result is of importance for understanding the physical mechanism of the detection in high electron mobility transistors and for development of a proper theoretical description of this process

Structural and Optical Properties of Antimony-Containing Epitaxial Layers Grown on GaSb by MOCVD

Experimental results on MOCVD epitaxy of some antimonides on GaSb substrates are presented. Specific technological problems, which effect in narrow window of process parameters, were overcome and good quality of GaSb/GaSb, InGaSb/GaSb and InGaAsSb/GaSb layers was obtained. Structural, optical and electrical characterisation data are shown and discussed. Developed technology can state a ground work for realisation of antimonide-based optoelectronic devices

MOCVD Growth of InP-Related Materials Using TEA and TBP

High quality epitaxial layers of GaAs, InP, AlAs, InGaAs, InGaP, InGaAlP have been grown by low-pressure metalorganic chemical vapor deposition using TMIn, TMGa, TMAl and the less hazardous group V precursors, ΤΒA, TBP. Excellent morphology was obtained for GaAs and InP in the temperature ranges of 570-650°C and 520-650°C, respectively. The V/III ratio as low as 1.5 was used to grow epilayers of InP. The 77 K mobility of InGaAs lattice matched to InP (grown with ΤΒA) was 72360 cm $\text{}^{2}$/(V s) for n = 1.5 × 10$\text{}^{15}$ /cm$\text{}^{-3}$ and a thickness of 2 μm. Comparable photoluminescence parameters of InGaP between layers grown with TBP and PH$\text{}_{3}$ were achieved, but for InGaAlP (TBP) photoluminescence intensity was significantly lower than for InGaAlP (PH$\text{}_{3}$). The promising results allow one to apply of ΤΒA and TBP for developing of device structures

Transport of Photoexcited Electron-Hole Plasma in GaN/AlGaN Quantum Well

We report spatially resolved photocurrent measurements showing transport of excitation on long distances in plane of a 6 nm GaN/$Al_{0.1}Ga_{0.9}N$ quantum well. The strong field present in nitrides (due to large spontaneous and piezoelectric polarizations) leads to lower recombination rates of electrons and holes, so in the case of electron-hole pairs excited by light, relatively long-lived electron-hole plasma could be generated. In the case of the investigated quantum well, lifetime of few μs was expected. The thermal measurements showed that barriers were low enough, so all excited carriers could reach the electrode (thermal activation energy of 0.11 eV was found). The diffusion length for unbiased structure was about 40 μm. It was observed that the charge transport could be clearly accelerated by bias. In the biased quantum well, the transport range was of the order of 100 μm under both positive and negative bias. The reported effect of long transport range is very important for electronic devices made on the GaN/AlGaN structures

Highly resonant graphene plasmon hotspots in complex nanoresonator geometries

Van der Waals surface polariton nanostructures are promising candidates for miniaturisation of electromagnetic devices through the nanoscale confinement of infrared light. To fully exploit these nanoresonators, a computationally efficient model is necessary to predict polariton behaviour in complex geometries. Here, we develop a general wave model of surface polaritons in 2D geometries smaller than the polariton wavelength. Using geometric approximation widely tuneable infrared nanoimaging and local work function microscopy, we test this model against complex mono-/bi-layer graphene plasmon nanoresonators. Direct imaging of highly resonant graphene plasmon hotspots confirms that the model provides quantitatively accurate, analytical predictions of nanoresonator behaviour. The insights built with such models are crucial to the development of practical plasmonic nanodevices

Investigation of Misfit Dislocation Sources in GaAs Epitaxial Layers

The formation of misfit dislocation was studied in GaAs homoepitaxiallayers on the substrates containing considerable amount of isoelectronic in-dium. The layers were grown with metal-oxide chemical vapour depositionand chemical vapour deposition methods including low temperature processwith tertiarbutylarsine arsenic source. The critical conditions of misfit dis-location formation were exceeded up to 5 x. The samples were examinedbefore and after epitaxial process with a number of different X-ray topo-graphic and diffractometric methods, including high resolution synchrotronwhite beam topography. The crystalIographic identification of the defectswas supported by the numerical simulation of topographic images. It wasfound that a number of threading dislocations, continuing in the epitaxiallayer from those existing in the substrate, did not take part in the formationof misfit dislocations despite a suitable slip system. On the other hand, theformation of misfit dislocations from small imperfections of epitaxial depositwas proved in many cases. A reasonable good quality of the 1ayers was con-firmed by the resolution of individual defects and only smalI broadening ofrocking curves