2019年11月6日星期三

Size and environment dependence of surface phonon modes of gallium arsenide nanowires as measured by Raman spectroscopy

Gallium arsenide nanowires were synthesized by gallium-assisted molecular beam epitaxy. By varying the growth time, nanowires with diameters ranging from 30 to 160 nm were obtained. Raman spectra of the nanowire ensembles were measured. The small linewidth of the optical phonon modes agree with an excellent crystalline quality. A surface phonon mode was also revealed, as a shoulder at lower frequencies of the longitudinal optical mode. In agreement with the theory, the surface mode shifts to lower wavenumbers when the diameter of the nanowires is decreased or the environment dielectric constant increased.

Source:IOPscience

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2019年10月30日星期三

Technology of production and magnetoelectric characteristics of multilayer structures nickel-tin on the gallium arsenide substrate

The technology of fabrication and the results of the magnetoelectric effect investigation in sandwich structure manufactured by galvanic deposition tin and nickel on the gallium arsenide substrate are presented. It is shown that the use of tin as an intermediate layer lead to reduces the mechanical stresses resulting on the interface nickel and gallium arsenide. It is possible to obtain qualitative structures with nickel layer thickness on the order of 100 microns. Experimental results of the frequency dependence of the magnetoelectric voltage coefficient in the region of electromechanical resonance are presented. The resonance value of the magnetoelectric voltage coefficient reached 40V/(cmcenterdotOe) with the Q-factor ≌ 700, which significantly exceeds the characteristics of similar structures obtained by bonding.



Source:IOPscience

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2019年8月22日星期四

Boron impurity anti-site defects in p-type gallium-rich gallium arsenide

It is shown that gallium arsenide crystals grown from gallium-rich melts encapsulated in boric oxide contain boron impurities, some fraction of which occupy arsenic lattice sites. In compensated material these acceptor defects are in negative charge state and give rise to infrared absorption due to localised vibrational modes (LVM) at 601 cm-1 (11BAs) and 628 cm 1(10BAs). The authors demonstrate for the first time that in p-type material neutral BAs defects are present although they give no detectable LVM absorption: their presence is revealed by tuning the position of the Fermi level, EF, to the point where it coincides with the acceptor electronic level. This is achieved by introducing deep-hole traps by electron irradiation and then fine tuning of EF is effected by varying the temperature of the sample. They estimate the BAs acceptor level to be somewhat greater than 0.2 eV above the valence band and there is a possibility that it is the previously reported level at 0.23 eV. The level at 0.077 eV is probably due to an intrinsic defect.



Source:IOPscience

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2019年8月9日星期五

Near-band-edge luminescence in heavily doped gallium arsenide

The near-band-edge photoluminescence at 80K of heavily tellurium-doped degenerate liquid-phase-epitaxial gallium arsenide layers (n=2*1018 cm-3) is investigated. The layers are compensated with shallow germanium acceptors (the values of the degree of compensation are K=0.05-0.7) during the epitaxial growth process. It is established that even at very low concentration of shallow acceptors (K=0.05), the so-called mobile band appears in the near-band-edge luminescence spectra. The peak energy of this band shifts to lower energies, the non-equilibrium carrier generation rate decreases and saturates at values E0T, which are considerably lower than those calculated for the filling of the valence band density-of-states tails. It is assumed that this discrepancy between theory and experiment is due to the uncertain knowledge of the pre-exponential term in the expression for the density-of-states tails and to the formation of some deeper fluctuation states when there is a considerable difference between the concentrations of shallow donors and acceptors. It is assumed that in this case some of these states act as associates.


Source:IOPscience

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2019年8月1日星期四

Degradation of Gallium Arsenide Crystals by the Cold-Working Treatment (Abrasion)

The effect of the cold working treatment on the characteristics of GaAs crystals was studied. Abrasion and subsequent heat treatment of the crystals decrease the carrier concentrations and increase the breakdown voltages. After abrading and subsequent heat treatment, the increase in etch-pit density in the crystals was observed. It is supposed that the degradation of the crystals was related to the generation of dislocations during such treatments.



Source:IOPscience

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2019年7月23日星期二

Parameters of an electron-beam-pumped double-doped gallium arsenide laser

An investigation was made of the laser action in compensated gallium arsenide doped with donors (Te or Sn) and acceptors (Zn). Such doping reduced considerably the threshold current density and the working voltage of electron-beam-pumped lasers. The lowest values of the threshold were 0.1 A/cm2 at T85°K and 1.5 A/cm2 at T300°K. The maximum efficiency reached 30% at T85°K and 21% at T300°K. A waveguide resonator structure ensured that these values of the threshold current and the efficiency were not affected when the electron energy was reduced from 50 keV to ~25 keV. A further redution of the electron energy to 9 keV caused the threshold current density to rise to 1.5 A/cm2 at T85°K.



Source:IOPscience

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2019年7月17日星期三

Detection of spin-states in Mn-doped gallium arsenide films

We show that isolated magnetic dipoles centred at the position of manganese impurities in a gallium arsenide lattice lead to spin polarized states in the bandgap of the III–V semiconductor. Spectroscopy simulations with a tungsten tip agree well with experimental data; in this case, no difference can be observed for the two magnetic groundstates. But if the signal is read with a magnetic iron tip, it changes by a factor of up to 20, depending on the magnetic orientation of the Mn atom.



Source:IOPscience

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