Identification of the phosphor vacancy defect in electron irradiated p-type Inp

A new EPR spectrum has been observed in electron irradiated p-type InP. The spectrum is isotropic, has an effective g-factor of 2.05 + 0.04 and a peak to peak linewidth of 1800 G. Its introduction rate R = 1 cm⁻¹ . We attribute this spectrum to the neutral phosphor vacancy V⁰_P.     

Low temperature electron transport in phosphorus-doped ZnO films grown on Si substrates

Low temperature magneto-transport properties and electron dephasing mechanisms of phosphorus-doped ZnO thin films grown on (1 1 1) Si substrates with Lu₂O₃ buffer layers using pulsed laser deposition were investigated in detail by quantum interference and weak localization theories under magnetic fields up to 10 T. The dephasing length follows the temperature dependence with an index p≈1.6 at higher temperatures indicating electron–electron interaction, yet becomes saturated at lower temperatures. Consistent with photoluminescence measurements and the multi-band simulation of the electron concentration, such behavior was associated with the dislocation densities obtained from x-ray diffraction and mobility fittings, where charged edge dislocations acting as inelastic Coulomb scattering centers were affirmed responsible for electron dephasing. Owing to the temperature independence of the dislocation density, the phosphorus-doped ZnO film maintained a Hall mobility of 4.5 cm² V⁻¹ s⁻¹ at 4 K.     

Photoenhancement of the photoconductivity (PC) of electron irradiated semiconducting diamond

The spectrum of the non-enhanced PC of electron irradiated semiconducting diamond extends from the UV towards the visible and near infrared. It's long wavelength tail was found in the present work to exhibit a well defined threshold shifted with temperature from about 1.5eV at 76 K to about 1.25 eV at 500 K. Pre-illumination in the “UV-band” produced an enhanced PC band with a temperature independent threshold at 1.08 0.03 eV. This photoenhanced band was found to be closely related to a thermally-simulated current peak (TSC) at 500 K with an activation energy of 0.50 eV excited by the pre-illumination in the UV-band. The prhotenhanced band was bleached out thermally with the exhaustion of the TSC peak below 600 K. Some of the characteristics of the photoenhanced band including the linear dependence of the square root of the PC on photon energy may suggest that internal photoemission of holes plays a role in the formation of this band.     

Nearly exponential dependence on photon energy of the photoconductivity of electron irradiated semiconducting diamond

The photoconductivity (PC) of electron irradiated semiconducting diamond was examined over the energy range 1–4 eV (0.3–1.2 μm) and over the temperature range 76–500 K. The PC response spectra exhibited a strong drop below 3 eV. In one sample (RDl) this drop was by a factor of nearly 10⁴ from 3 to 2 eV. In the range of the Ar laser lines (2.41–2.73 eV) the PC depended nearly exponentially on photon energy. A mechanism involving competition for the absorption of the exciting light between the non-photoconductive GRl system and the photo-conductive UV absorption band gives a good account of the experimental results. This includes the photon energy dependence of the PC and its thermal dependence.The proposed mechanism is further supported by the absence of the drop in PC near 2.5 eV in a lightly colored electron irradiated diamond.     

Room temperature magnetoresistance anisotropies in p-type (001) Si on sapphire

Magnetoresistance anisotropies, differing from those of bulk p-type Si, have been observed on p-type Si film on sapphire (SOS). They may arise from the valence band split and deformed by a large compressive strain due to thermal expansion coefficient difference between Si and sapphire.     

High temperature defects in electron irradiated semiconductors HgCdTe,PbSnTe

The peculiarities of defect formation in n- and p-type conductivity HgCdTe and PbSnTe crystals after electron irradiation (2 MeV, 300 K) up to 2 × 10¹⁸ cm^-2 are examined. It has been found that irradiation results in formation of n-type conductivity crystals with final parameters that are determined by the composition of initial samples. The annealing of radiation defects occurs in the 360–470 K temperature range. It has been believed that the change of HgCdTe, PbSnTe properties after electron irradiation at 300 K are connected with formation of radiation defects, including Te vacancies.     

Sharp line photoconductivity in Si: S

Fine structure due to photothermal processes has been studied in the photoconductivity spectrum Si: S. For three levels (transitions of neutral donors with binding energies 109.5, 187.2 and 318.4 meV) excited states up to and including 4 p_± are observed with linewidths limited by system resolution (? 0.2 meV). A new level is also tentatively identified with binding energy 0.155 eV. Resonance structure is observed in the continuum spectra of the two deepest levels due to excited state phonon replicas. The effect of electric fields up to 2 kV cm^-1 is reported: the threshold shifts to lower energies, and highly excited states disappear, and a new line is observed.     

Low temperature electron irradiation of tellurium

Abstract

Tellurium single crystal samples with a hole concentration of 3 × 10¹⁴/cm² were irradiated at 10 K with electrons with an energy of 0.6 and 1 MeV. In the range investigated resistivity and Hall-coeficient R_H both decreased linearly with the integrated electron flux. The hole generation rate was 0.09 cm^?1 and 0.47 cm^?1 for 0.6 and 1 MeV electrons, respectively. The Hall-mobility R_H/P increased with irradiation.

Annealing of the radiation damage by raising the temperature clearly revealed three recovery stages in the resistivity- and Hall-data. At 180K p and R_H returned to their pre-irradiation values. The original Hall-mobility was already restored close to 90 K.

A more detailed study of the first recovery stage, which occurs at about 50 K, revealed an activation energy of 170±40meV. It is most likely, that the observed lattice defects are Frenkel-defects. There are indications, that the point defects interact with dislocations.     

Polarization dependence of intersubband absorption and photoconductivity in p-type SiGe quantum wells

We present a detailed study of the polarization dependence of subband absorption and photoconductivity in Si/SiGe quantum wells. For samples with a hole concentration ofp_s2.8×10¹² cm², bothp- ands-polarized absorptions have been observed and transitions to several excited states are clearly identified by comparison with self-consistent Luttinger-Kohn type calculations. The photoconductivity is surprisingly insensitive to the polarization, which indicates the importance of the subsequent transport process on the photocurrent responsitivity.     

Low temperature dependence of the elastic constant c44 of p-type silicon

We present a theory of the change of the elastic constant c₄₄ in Si due to the presence of acceptor impurities. The magnitude of this change increases rapidly as the temperature is lowered below a critical temperature which we associate with the onset of a rapid freezing out of the charge carriers. This variation is not so pronounced in heavily doped samples where freeze-out does not take place even at the lowest temperatures. It is also necessary to consider that the acceptor states have a split ground state in the absence of an ultrasonic wave arising from random local strains.     

Influence of annealing on the conductivity and photoconductivity of p-type CdTe

On annealing p-type CdTe, considerable change in conductivity takes place. Samples of high resistivity were used for the measurements. Each of a set of samples was annealed at different temperature. After annealing, the temperature dependence of the conductivity and the relaxation curves of the photoconductivity were measured. Analysis of the first set of curves yielded value of energyE _a corresponding to the level occurring in given samples. It was established that this acceptor level is due to V^cd, or V^cd complexes, and is situated at 0.3 eV above the valence band edge. Concentration of these levels is increased by annealing. Furthermore, an energy value ofH=0.79 eV was found, corresponding very probably to the formation energy of a vacancy V^cd.Analysis of the relaxation curves yielded the temperature dependence of _S , _T and the energy distanceE _M of the impurity level that is responsible for photoconductivity. A value of (E _g -E _M )=0.09–0.12 eV was found for all samples studied. This level therefore lies below the conduction band edge and its concentration amounts to 10¹⁴–10¹⁵ cm^–3. The level is probably due to foreign impurities.Two sets of samples were used: both as-grown and Sb-doped. The results for both sets were not much different from each other.Ke Karlovu 3, Praha 2, Czechoslovakia.     

Annealing of point defects in p-type germanium after electron irradiation at liquid nitrogen temperature

Annealing of radiation induced defects in p-type germanium was studied by measuring Hall coefficient and conductivity. The dopant was gallium or indium. It was concluded that the annealing stage between 80° and 140°K is caused by migration of the vacancy to the sink of an impurity atom. In this stage the vacancy migrates to a substitutional impurity atom and makes an association. The activation energy of the stage was found tO be 0.1 ev ad it is regarded to be that of the vacancy migration. The model for the annealing stage which occurs in the range 220 to 270°K is proposed as follows: An interstitial impurity atom migrates to a substitutional impurity atom and makes an association. From the activation energy of the stage, the migration energy of the interstitial impurity atom was concluded to be about 0.4 eV for gallium and 0.7 eV for indium atoms.     

On-line DLTS investigations of vacancy related defects in low-temperature electron irradiated, boron-doped Si

Vacancy-related defects in Si are explored with deep level transient spectroscopy (DLTS). The measurements are performed on-line on irradiated p-type Si and a new trap with the signature (E_pa, _pa) = (0.18 eV, 6.5×10^-15 cm²) – only present at cryogenic temperatures – is studied. Furthermore, the bi-stable boron-vacancy complex is studied and its configuration at low temperatures is investigated and found to have the signature (E_pa, _pa) = (0.11 eV, 8.2×10^-15 cm²). PACS 71.55.Cn; 61.80.Fe; 61.82.Fk; 61.72.Ji     

Low temperature electron spin resonance of the Kondo ion in a heavy fermion metal: YbRh2Si2

We report an electron spin resonance (ESR) study on single crystals of the heavy fermion metal YbRh2Si2 which shows pronounced non-Fermi liquid behavior related to a close antiferromagnetic quantum critical point. It is shown that the observed ESR spectra can be ascribed to a bulk Yb3+ resonance. This is the first observation of ESR of the Kondo ion itself in a dense Kondo lattice system. The ESR signal occurs below the Kondo temperature (T(K)) which thus indicates the existence of large unscreened Yb3+ moments below T(K). We observe the spin dynamics as well as the static magnetic properties of the Yb3+ spins to be consistent with the results of nuclear magnetic resonance and magnetic susceptibility.     

Low temperature reorientation of Fe spins in an irradiated hematite single crystal

Irradiation with alpha-particles of 29 and 50 MeV energies leads to essential changes in magnetic properties of hematite single crystals. When temperature decreases, the number of iron ions with high-temperature spin orientation decreases too but does not disappear completely, and at helium temperatures, in contrary, increases (the new transition). Appearance of the new transition is explained by superparamagnetic behaviour of the disordered zones produced by atom-atomic collision cascades. The splitting of the Müssbauer spectra in the temperature interval of the Morin transition as well as at the new transition undoubtedly shows that the both transitions are transitions of the first order.     

Low temperature electron mobility in a coupled quantum well system

We study low temperature electron mobility μ_nin a GaAs/Al_x Ga _1 − xAs coupled double quantum well structure. Both the extreme barriers are δ -doped with Si so that the electrons diffuse into the adjacent wells forming two sheets of two-dimensional electron gas (2DEG) separated by a thin central barrier. The subband electron wavefunctions and energy levels are numerically obtained as a function of the well width, barrier width and doping concentration. The screening of ionized impurity potential by the 2D-electrons is obtained in terms of the static dielectric response function within the random phase approximation (RPA). μ_nis calculated by solving the coupled Boltzmann equation in the relaxation time approximation. The coupling of wavefunctions through the barrier, screening of ionized impurities and intersubband scattering effects on μ_nare investigated.