Deep traps in GaAs under hydrostatic pressure

The influence of hydrostatic pressure on the energy levels of eight different deep traps in GaAs is determined by means of a transient capacitance technique. Hydrostatic pressure coefficients are shown to be decisive parameters in order to distinguish isoenergetic traps of different origin. For the EL6-, the M3- and the E3-traps (E_c?0.31eV), strongly different pressure coefficients are found. The HK1- and HK2- hole traps exhibit only small pressure coefficients relative to the valence band edge.     

Electrical resistance of Fe-Zr and Fe-Ni-Zr amorphous alloys under hydrostatic pressure

The effect of pressure on the electrical resistance of Fe₉₀Zr₁₀ and (Fe_0.96Ni_0.04)₉₀Zr₁₀ amorphous alloys has been investigated. The minimum point in the electrical resistance versus temperature curve shifts toward lower temperature range with increasing hydrostatic pressure, corresponding to the shift of the Curie temperature. The decrement of the electrical resistance below the Curie temperature T_c is about twice that above T_c, suggesting a large compressibility in the ferromagnetic state of the amorphous Invar alloys.     

Electrical properties of TlGaTe2 single crystals under hydrostatic pressure

The effect of hydrostatic pressure (up to 0.82 GPa) on the electric properties of chain TlGaTe₂ single crystals has been investigated in the temperature range 77-296 K. It has been shown that pressure leads to a considerable increase of conductivity (σ_⊥) across the chains of TlGaTe₂ single crystals. Parameters of localized states in the band gap of TlGaTe₂ single crystal according to the low-temperature electrical measurements were obtained at various pressures.     

GaAs/AIAs superlattices under pressure: steady-state and subpicosecond time-resolved measurements

Abstract

Low-temperature photoluminescence measurements under hydrostatic pressure were performed on [100]-, [311]-and [111]-grown GaAs/AlAs superlattices. The indirect optical transitions for all three growth directions were identified by their characteristic pressure dependences as originating from the X point of the AlAs conduction band. Subpicosecond-time-resolved measurements on a GaAs/AIAs superlattice show a decrease of electron transfer times from the GaAs layer into the A1As layer with pressure from 400 fs to 5Ofs and an intensity dependence of the pressure-induced crossover from type I to type II.     

Short-range resonant electron scattering in Se- and S-doped GaxIn1-x Sb under hydrostatic pressure

Abstract

Electron scattering mechanisms have been investigated in Se- and S-doped Ga_xIn_1-xSb alloys by measuring the Hall mobilities as a function of hydrostatic pressures up to 25 kbar at temperatures down to 4.2 K. The analysis of the data shows that the Brooks-Herring theory of ionized impurities scattering could fit the experimental variations only overa narrow range of low pressures before carrier freeze-out into a resonant impurity level sets in. At higher pressures, good agreement between theory and experiment could be obtained by introducing an additional scattering mechanism due to the short-range central cell impurity potential.     

Electrical resistance measurements under pressure on NbTe2 single crystal

Transition metal dichalcogenides, because of their layered structure, are well suited for extreme pressure lubrication. These materials being semiconducting and of layered structure may undergo structural and electronic transitions under pressure. Here we report the details of the preparation and characterization of single crystals of NbTe₂ and the results of electrical resistance measurements under pressure carried out on it to investigate this possibility. Single crystals were grown by the chemical vapor transport technique, using iodine as a transporting agent. The composition of the grown crystals was confirmed on the basis of Energy Dispersive Analysis by X-ray (EDAX) and remaining structural characterization was also accomplished by X-ray Diffraction (XRD) studies. Electrical resistance was measured employing a Bridgman anvil set up to 10?GPa and diamond anvil cell (DAC) assembly up to 25?GPa. A technique slightly modified from that described in the literature for carrying out electrical resistivity measurements in the diamond anvil cell (DAC) under pressure has been standardized.     

Defects with deep levels induced by plastic deformation and electron irradiation in El2-free GaAs

Abstract

Defects with deep electronic energy levels induced by electron irradiation at room temperature or plastic deformation at 450°C in GaAs in which grown-in EL2 defects are previously eliminated by heat-treatment are investigated by means of measurements of the optical absorption and the Hall effect. Thermal stabilities of the induced defects are studied by tracing the changes mainly in the absorption specturm due to isochronal annealing. The absorptions both in deformed and irradiated specimens are mostly photo-unquenchable. Therefore, the defects induced by above two procedures are identified not to be EL2. Semi-insulating or n-type specimens convert to p-type by plastic deformation or electron irradiation, showing that high densities of acceptors are generated by the above two procedures.     

Photoluminescence of GaSb under hydrostatic pressure

Photoluminescence measurements on GaSb samples were carried out at low temperatures (2 – 5 K) and high pressures (0 – 9 kbar). The energy shift of the direct gap was determined: $\text{d}\text{E}{}^{\mathrm{\Gamma }}\text{/dP= 14.5± 0.3 meV/kbar}$. At pressures above 8 kbar the spectra showed additional structure from the indirect L-conduction band minima. The energy shift of the L-conduction bands were determined: $\text{d}\text{E}\text{L/d}\text{P}\text{= 5.5± 1. meV/kbar.}$ From these data the critical pressure for the inversion of the two conduction bands was calculated: $\text{p}{}^{\mathrm{h}}{}_{\mathrm{c}}\text{= 10.5 ± 1. kbar}$.     

Electroreflectance in GeSi alloys under hydrostatic pressure

From the electroreflectance spectra measured under hydrostatic pressure to 7 kbar we have determined the pressure coefficients for germanium (dE₁/dP = 7.8 ± 0.4⁻⁶eV/bar, dP = 1.4 ± 0.8 10⁻⁶eV/bar), for Si (dE′_o/dP = 1 ± 1 10⁻⁶eV/bar, dE₁dP = 6.2 ± 0.4 10⁻⁶eV/bar) and for GeSi alloys in the entire composition region. For the composition 80–100% of Si which is widely discussed in the literature, we could distinguish two maxima with substantially different pressure coefficients. The absolute experimental values of dE/dP agree rather well with theoretical values which, together with composition shift of electroreflectance peaks, enable us to connect the peak E₁ predominantly with λ and L and E′_o with Г and Δ transitions in the entire composition region.     

Raman scattering in GaTe under hydrostatic pressure

Raman-active lattice vibrational modes of GaTe have been investigated at 300 K in the range 15–300 cm^?1 in equilibrium conditions under different hydrostatic pressures up to 11.25 kbar. The spectra of the Bridgman grown crystals were excited with the 1.06 μm line of the continuously operated YAG:Nd³⁺ laser. The mode-Grüneisen parameters $\text{Γ}{}_{\mathrm{j}}\text{= (}\text{1}\text{β}\text{)(}\text{1}\text{ν}{}_{\mathrm{j}}\text{) =}\text{dν}{}_{\mathrm{j}}\text{d}{}_{\mathrm{p}}$ were determined for all fourteen Raman bands observed. It is shown that there is no low frequency rigid-layer modes or Davydov pairs in Raman spectra of GaTe crystals.     

Magnetization measurements on a single crystal of CeAl2 under high magnetic field and hydrostatic pressure

Magnetization measurements have been carried out at low temperature in CeAl₂ under magnetic fields up to 80 kOe and hydrostatic pressures up to 18 kbar. A strong decrease of the magnetization of cerium with pressure indicates the close proximity of the cerium 4f level to the Fermi energy.     

DLTS investigation of GaP under hydrostatic pressure

Abstract

Deep Level Transient Spectroscopy (DLTS) was applied to nitrogen related deep electron trap 0.4 eV in green emitting diodes of GaP under hydrostatic pressure. The pressure coefficient of the level energy is determinated as equal -31 meV/kbar with respect to the valence band edge.