Hall mobility of undoped n-type conducting strontium titanate single crystals between 19 K and 1373 K

The Hall mobility of undoped n-type conducting SrTiO₃ single crystals was investigated in a temperature range between 19 and 1373 K. Field calculations were used to estimate the influence of sample shape and electrode geometry on the measured values. Between 19 and 353 K samples, which were quenched under reducing conditions, show an impurity scattering behavior at low temperature and high carrier concentrations and a phonon scattering mechanism at room temperature. In this temperature region, no carrier-density-dependent mobility was found. In conjunction with measurements of the mass difference before and after reoxidation, the oxygen deficiency and the oxygen vacancy concentration could be determined. The oxygen vacancies proved to be singly ionized. Above 873 K, Hall mobility and carrier concentration had been determined as a function of both oxygen partial pressure and temperature for the first time. In this temperature range the mobility does not depend on carrier concentration, but shows aT ^–1.5 dependence.     

Defect behaviors in n-channel power VDMOSFETs during HEFS and thermal post-HEFS annealing

The results of positive/negative Fowler-Nordheim high electric field stress and thermal post-high electric field stress annealing of commercial n-channel power VDMOSFETs have been presented. They have shown that gate bias sign has an influence on the fixed trap behavior during high electric field stress, but has no influence on any defect type behavior during thermal post-high electrical field stress annealing. In addition, slow switching traps have different behavior, but fast switching traps have the same behavior during thermal post-high electrical field stress annealing and thermal post-irradiation annealing.     

Hall mobility of amorphous Ge2Sb2Te5

The electrical conductivity, Seebeck coefficient, and Hall coefficient of three-micron-thick films of amorphous Ge₂Sb₂Te₅ have been measured as functions of temperature from room temperature down to as low as 200 K. The electrical conductivity manifests an Arrhenius behavior. The Seebeck coefficient is p-type with behavior indicative of multi-band transport. The Hall mobility is n-type and low (near 0.07 cm²/V s at room temperature).     

Photo production of surface recombination centers in gallium arsenide

The near band edge photoluminescence (–870 nm) at 300 K of semi-insulating and p-type GaAs, a potentially useful tool for GaAs wafer mapping, decreases with time under illumination from the 514 nm line of an Ar⁺ laser. The photoluminescence bleaching has been studied by optical and photo Hall-effect techniques. It recovers only partially on a time scale of days and does not show a distinct intensity threshold behavior. From lifetime measurements and experiments on samples covered with epitaxial layers of GaAs _x P_1–x or Si₃N₄ it is concluded that creation of surface recombination centers causes the PL bleaching.     

In-situ formation of p-n junctions in semiconducting TiO2

Application of small voltages in the range from 0.5 V to 1 V to an originally homogeneously Fe-doped (0.5 mol-%) TiO₂ semiconductor at temperatures between 700° C and 750° C caused the formation of a p-n junction within the sample. This is indicated by a change of the U-I characteristics from a symmetrical to a diode type behavior. By inversion of the polarity of the applied voltage, the p-n junction could be removed. This process is completely reversible. The results are explained by an asymmetric change in the concentration of lattice defects, which act as dopants in addition to the extrinsic dopants, caused by the application of the voltage to the sample.     

Arsenic-implanted polysilicon layers

The diffusion behavior of implanted arsenic in polycrystalline silicon was investigated, using backscattering and electrical measurements. The diffusion coefficient isD=8.5×10⁻³ exp (−2.74/kT) for polycrystalline silicon deposited on freshly-etched silicon andD=1.66 exp (−3.22/kT) for the deposition on silicon having natural oxide. At the interface to the single-crystalline silicon, a pile-up of arsenic occurs, which depends also on the surface treatment prior to the deposition of the polycrystalline silicon.     

A new combination of scattering mechanisms for transverse runaway (TR) of hot electrons

A new combination of energy and momentum scattering mechanisms has been found at which the transverse runaway (TR) of hot electrons takes place. Up to now only two combinations of scattering mechanisms at which TR occurred have been known. These two combinations were obtained by analytical solution of a complex integral equation at certain approximations. In the present work, using modern numerical methods, with no above-mentioned approximations, a solution of the integral equation for a new combination of scattering mechanisms has been found.In the work physical conditions responsible for dominance of corresponding scattering mechanisms are also analyzed.     

Magnetoplasma waves in anisotropic semiconductors and semimetals

The propagation of electromagnetic waves in solids with electron and hole energy surfaces of second order placed in a magnetic field is investigated. The deduced dispersion relation is compared with measurements of the Alfvén wave velocity in bismuth. The theoretical and experimental results are in good agreement. In particular, it is clearly shown that for special orientations of the magnetic field switching from one mode to the other occurs. Parameters of the energy surfaces of bismuth are given by fitting the theoretical curves to the measured phase velocity diagrams.     

The large anisotropy of the magnetic and transport properties in the Ba5Co5ClO13 single crystal

In this Letter, the single crystals of Ba₅Co₅ClO₁₃ were grown by the flux method successfully. Their structure, magnetic and transport properties were studied. A large anisotropy of the magnetic and transport properties has been detected in this compound. Below the TN∼108 K, the magnetic susceptibility exhibits an antiferromagnetic peak in χc and an upturn transition in χab. We suggest that this behavior is consistent with the competition of the ferromagnetic (FM) intra-blocks coupling and antiferromagnetic (AFM) inter-blocks coupling in this compound. The temperature dependence of the resistivity displays a hump in ρab and a kink in ρc around TN, suggesting the strong coupling between the transport and magnetic properties. Above and below the transition, the transport properties in ab plane follow the three-dimensional (3D) variable range hopping (VRH) mechanism.     

Relaxation semiconductors: In theory and in practice

Relaxation semiconductors are materials dominated by free carrier transport and defined by the condition that the dielectric relaxation time _D is longer than the free carrier lifetime ₀. Novel transport behavior has been demonstrated, both theoretically and experimentally, to be associated with this regime of semiconductor behavior. This review surveys the history of the field, emphasizes recent experimental and modeling work and summarizes our current understanding of relaxation behavior in crystalline semiconductors.Dedicated to H.-J. Queisser on the occasion of his 60th birthday     

High electric-field hall effect measurements onn-type InSb at 77 K

Pulsed Hall-effect experiments onn-type InSb at 77 K, with nanosecond time resolution, at magnetic inductions down to 2 mT and for electric field strengths up into the avalanche regime are reported. Results on mobility are compared with previous experimental data and various theoretical calculations. For the first time also results on the scattering factor as a function of electric field are given. A curious time dependent behaviour of the transverse voltage under avalanche conditions is reported. Along with the development of the avalanche the transverse voltage decreases and may even change sign. This phenomenon is qualitatively explained in terms of the magnetoconcentration effect and the change of contact properties under avalanche conditions.     

Electrical properties of the AgTlSe2 semiconductor in the liquid state

The electrical conductivity and thermoelectric power of AgTlSe₂ have been investigated as a function of temperature from 390° C up to 590° C. The experimental data are analyzed in terms of a model developed for the density of states and electrical transport in solid amorphous semiconductors [12]. Positive thermoelectric power suggests a large predominance of holes in electrical conduction. It appears that the conduction is due to holes in localized states near the band edge.     

Mechanism for NonlinearI – V Behaviour and the Temperature Dependence of Threshold Switching in the Se-Te-Sn System

The nonlinearI – V behaviour and threshold switching of the bulk Se-Te-Sn system have been experimentally studied at various temperatures. It is observed that the curves are linear for low voltages and become superlinear at higher voltages. After a certain voltageV _th, the current through the material shoots to a very high value and the potential across the material drops to a low value. It is also found that there is a decrease in Vh with increase in percentage of tin and temperature. An attempt is made to explain the nonlinearI – V behaviour and threshold switching on the basis of a microcrystallite model. A study of Se-Te-Sn system reveals that our results are in concurrence with the theoretical predictions.     

Mode mixing of Alfvén waves in bismuth

We have investigated the propagation of Alfvén waves in bismuth at 4.2 K using a microwave interferometer at 34.45 GHz and applying magnetic fields up to 1 Tesla. At certain angles between the external magnetic field and the direction of propagation of the Alfvén waves in the crystal, we have observed intense oscillations of the amplitude and the phase of the interferometer curves. We explain these oscillations as due to a superposition of the two Alfvén wave modes. The phase velocities of the two modes are calculated from the measurements. Comparing them with a general dispersion relation we find good agreement between the theoretical phase velocities and the experimental values.     

Hopping and band transport in amorphized semiconductors

Crystalline samples of Si, GaAs, GaP, InP, and CdTe have been rendered amorphous by bombardment with rare gas ions. DC conductivity and thermopower have been measured as a function of temperature in the interval between 15–500 K. In all cases, electron transport at low temperatures is characterized by non-simply activated processes of the hopping type transport, whereas band transport is observed at higher temperatures. The common and individual features of the different amorphous systems are discussed within the framework of existing transport theories.     

Electron mobility of Sr1-xLaxTiO3 ceramics between 600 °C and 1300 °C

1-x La_xO₃ ceramics (0.003<x<0.40) were measured between 600 °C and 1300 °C. The density of electrons in the conduction band was determined from Hall and thermopower measurements. A chemical approach (Ti³⁺-titration) confirmed these results. The electron mobility was calculated by combining charge carrier density and conductivity data. The temperature dependence of the mobility obeys a power law. Its exponent varies from -1.5 for slightly doped samples (x=0.003) to -2.74 for lanthanum-rich samples (x=0.4) indicating a phonon scattering controlled transport behavior. The mobility data obtained from slightly doped ceramic samples agree very well with Hall mobilities found in undoped SrTiO₃ single crystals. Received: 22 January 1997/Accepted: 1 April 1997     

Thermal annealing and light irradiation effects on hole and electron drift mobilities of Se93.5As6.5 and Se94.3Ge5.7 films

Thermal annealing and light irradiation effects on hole and electron drift mobilities were studied for amorphous Se_93.5As_6.5 and Se_94.3Ge_5.7 films by means of a time-of-flight technique. The electron drift mobility and its activation energy show a drastic increase after the heat and light treatments, while the hole drift mobility remains almost unchanged. The change of electron transport is attributed to a relaxation of local structural distortion, which is correlated with relatively shallow localized states. The present experimental results are inconsistent with the prior proposal that electron transport in amorphous selenides is correlated with Se₈ ring molecules.     

Electrical conductivity and thermoelectric power of AgInSe2 in the solid and liquid states

The electrical conductivity and thermoelectric power of AgInSe₂ have been investigated as a function of temperature from 420°C to 950°C. Experimental data are analyzed in terms of a model developed for the density of states and electrical transport in solid amorphous semiconductors [1]. The activation energy calculated from electrical conductivity data is found to be 0.06 eV for the solid and 0.37 eV for the liquid phase. Moreover, the coefficient of the linear decrease of the energy gap with temperature was found to be 1.96×10^–4 eV/K.     

Edge current switch of two-dimensional electron gas using carrier density control

We have investigated the effects of electron density discontinuity on the transports of edge currents of two-dimensional electron gas (2DEG). The electric field applied to a gate, which covers the 2DEG partially, gives rise to change in the carrier density and results in a density gradient, which deforms the edge currents. The transverse and longitudinal resistances were measured as functions of gate voltage V_G in the quantum Hall regime. The deviations of the longitudinal resistances from the normal quantum Hall resistances are attributed to the reflections of the edge currents under the influence of the abrupt density discontinuity. A switching behavior of the transverse resistance by controlling the gate voltage was observed when V_G=−2.2 and −2.0 V for magnetic field H=5 and 7.2 T, respectively.