We report on hot electron induced impact ionization and large room-temperature magnetoresistance (MR) in micron-sized channels of $n$-type high-mobility InAs $(\ensuremath{\mu}=3.3{\mathrm{m}}^{2}{\mathrm{V}}^{\ensuremath{-}1}{\mathrm{s}}^{\ensuremath{-}1}$ at $T=300\mathrm{K})$: the MR reaches values of up to 450% in magnetic fields of 1 T and applied voltages of \ensuremath{\sim}1 V and is weakly dependent on temperature. We present Monte Carlo simulations of the hot electron dynamics to account for the large MR and its dependence on the sample geometry and applied electric and magnetic fields. Our work demonstrates that the impact ionization of electrons at room temperature, under small applied magnetic fields (1 T) and small voltages (1 V), can provide an extremely sensitive mechanism for controlling the electrical resistance of high-mobility semiconductors.
We measure the current due to electrons tunneling through the ground state of hydrogenic Si donors placed in a GaAs quantum well in the presence of a magnetic field tilted at an angle to the plane of the well. The component of B parallel to the direction of current compresses the donor wave function. By measuring the current as a function of the perpendicular component of B, we probe how the magnetocompression affects the spatial form of the wave function and observe directly the transition from Coulombic to magnetic confinement at high fields.
We report large amplitude quantum oscillations and negative differential conductance in the bias voltage-dependent photocurrent of p-i-n GaAs diodes with an AlAs barrier in the intrinsic ($i$) region. The oscillations appear only when the devices are illuminated with above-band gap radiation. They are strongly suppressed by a weak (\ensuremath{\sim}2 T) in-plane magnetic field. Their period, amplitude, and magnetic field dependence are explained in terms of the quantized motion of confined photoexcited electrons and holes in the triangular potential wells formed by the AlAs barrier and the strong electric field in the intrinsic region. With increasing electric field, the energy levels of the electrons (holes) successively reach the top of their confining potentials, thus leading to a larger overlap of their wave functions with the free carriers in the $p$- (and $n$-) doped electrodes and to the observed oscillatory modulation of the recombination rate and photocurrent as a function of the applied voltage. The effect on the photocurrent oscillations amplitude of placing a layer of InAs quantum dots in the AlAs barrier layer is also examined.
We show that the dissociation of the N-H complex in hydrogenated III-N-Vs can be laser activated at temperatures that are significantly smaller than those (>200 \ifmmode^\circ\else\textdegree\fi{}C) required for thermal dissociation due to a resonant photon absorption by the N-H complex. This phenomenon provides a mechanism for profiling the band-gap energy in the growth plane of the III-N-Vs with submicron spatial resolution and high energy accuracy; the profiles are erasable and the alloys can be rehydrogenated making any nanoscale in-plane band-gap profile rewritable.
Abstract We describe the synthesis and characterisation of the first of a new class of soluble ladder oligomeric thermoelectric material based on previously unutilised ethene-1,1,2,2-tetrasulfonic acid. Reaction of Ba(OH) 2 and propionic acid at a 1:1 stoichiometry leads to the formation of the previously unrecognised soluble [Ba(OH)(O 2 CEt)]⋅H 2 O. The latter when used to hydrolyse 1,3,4,6-tetrathiapentalene-2,5-dione (TPD), in the presence of NiCl 2 , forms a new material whose elemental composition is in accord with the formula [(EtCO 2 Ba) 4 Ni 8 {(O 3 S) 2 C = C(SO 3 ) 2 } 5 ]⋅22H 2 O ( 4 ). Compound 4 can be pressed into pellets, drop-cast as DMSO solutions or ink-jet printed (down to sub-mm resolutions). While its room temperature thermoelectric properties are modest (σ max 0.04 S cm −1 and Seebeck coefficient, α max − 25.8 μV K −1 ) we introduce a versatile new oligomeric material that opens new possible synthetic routes for n-type thermoelectrics. Graphical Abstract
We demonstrate that β-In2Se3 layers with thickness ranging from 2.8 to 100 nm can be grown on SiO2/Si, mica and graphite using a physical vapour transport method. The β-In2Se3 layers are chemically stable at room temperature and exhibit a blue-shift of the photoluminescence emission when the layer thickness is reduced, due to strong quantum confinement of carriers by the physical boundaries of the material. The layers are characterised using Raman spectroscopy and x-ray diffraction from which we confirm lattice constants c = 28.31 ± 0.05 Å and a = 3.99 ± 0.02 Å. In addition, these layers show high photoresponsivity of up to ∼2 × 103 A W−1 at λ = 633 nm, with rise and decay times of τr = 0.6 ms and τd = 2.5 ms, respectively, confirming the potential of the as-grown layers for high sensitivity photodetectors.
We study the conductivity of a two-dimensional electron gas in modulation-doped n-type ${\mathrm{GaAs}}_{1\ensuremath{-}y}{\mathrm{N}}_{y}/(\mathrm{AlGa})\mathrm{As}$ quantum well heterostructures. We find that the nature of the electrical conduction in the ${\mathrm{GaAs}}_{1\ensuremath{-}y}{\mathrm{N}}_{y}$ channel is band-like or hopping-like depending on N content, carrier concentration, and temperature. We show that when there is a sufficient carrier concentration in the channel, the conduction occurs through the extended conduction band states of ${\mathrm{GaAs}}_{1\ensuremath{-}y}{\mathrm{N}}_{y}.$ In this band conduction regime the electron mobility is shown to be limited by electron scattering by nitrogen atoms. This mechanism dominates over inelastic collisions by phonons even at room temperature.
During growth of the dilute p-type ferromagnetic semiconductor Ga1-xMnxAs, interstitial manganese, Mni(2+), is formed when x exceeds 2%. The double donor Mni(2+) compensates the free holes that mediate ferromagnetism. Annealing causes out-diffusion of these interstitials, thereby increasing the Curie temperature. Here, we use cross sectional scanning tunneling microscopy and spectroscopy to visualize the potential landscape which arises due to the clustering of Mni(2+) in annealed p-i-n (GaMn)As-GaAs double barrier heterostructures. We map the local minima in the potential landscape, link them to clusters of individual Mni(2+) ions, and show that the ions are doubly charged.
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