C. Canali

A review of some charge transport properties of silicon

This paper reviews the present knowledge of charge transport properties in silicon, with special emphasis on their application in the design of solid-state devices. Therefore, most attention is devoted to experimental findings in the temperature range around 300 K and to high-field properties. Phenomenological expressions are given, when possible, for the most important transport quantities as functions of temperature, field or impurity concentration. The discussion is limited to bulk properties, with only a few comments on surface transport.

Drift velocity of electrons and holes and associated anisotropic effects in silicon

Abstract The drift velocity of electrons and holes in high purity silicon has been measured, with the time of flight technique, as a function of electric field (0·1–50 KV/cm) at several temperatures between 77 and 300°K. By applying the electric field parallel to the and crystallographic directions, an evident longitudinal anisotropy effect has been found for the drift velocity of electrons and also, for the first time, for the drift velocity of holes. At high values of the electric field a saturation drift has been found for the electrons at the temperatures considered in these experiments. On the contrary, no saturation has been attained for holes, even at the highest applied electric fields. The ohmic mobility has been measured between 77 and 300°K for electrons and between 160 and 300°K for holes. When a comparison is possible, our results are in good agreement with other experimental results found in the literature. A qualitative theoretical interpretation of the effects observed is given.

Electron effective masses and lattice scattering in natural diamond

Abstract We report experimental evidence of the Si-like conduction band of natural diamond. A Monte Carlo analysis of electron drift velocity data enables for the first time the electron effective masses to be determined.

Charge Carrier Transport Properties of Semiconductor Materials Suitable for Nuclear Radiation Detectors

Charge carrier drift velocities in semiconductor materials suitable for solid state detectors has been reviewed. Si, Ge, CdTe and GaAs are considered. New data for HgI2 recently obtained are also reported. The data cover a large range of temperatures (6-430 K) and electric fields up to 50 KV/cm. An anisotropy effect in the drift velocity obtained by applying the electric field parallel to different crystallographic axis is also discussed for the case of Si and Ge.

Charge transport in layer semiconductors

Electron and hole-drift velocity is measured in the layer semiconductors HgI2, GaSe, PbI2 and GaS, mainly on the direction parallel to the c-axis between 80 and 400 K. In the electric field range in question, electron and hole-drift velocity is proportional to the field except in the case of GaS, where a superohmic behaviour is observed. At 300 K the mobility parallel to the c-axis is μe, = 100 cm2Vsec, μh = 4 cm2Vsec for HgI2; μe = 80 cm2Vsec, μh = 210 cm2Vsec for GaSe; μe, = 8 cm2Vsec, μh = 2 cm2Vsec for PbI2. The highest hole mobility observed in GaS is μh = 80 cm2Vsec. Where it is possible to compare these data with mobility values perpendicular to the c-axis, the three-dimensional character of the energy bands near the fundamental gap is proved. For HgI2 and GaSe we find no evidence for the large anisotropy of charge-carrier transport properties usually attributed to layered semiconductors. The mobility-temperature dependences found are interpreted on the basis of polar and non-polar optical phonon scattering mechanisms, except in the case of GaS, where a trapping model is used. The effective masses of electrons and holes are reported for PbI2 and, for the first time, for HgI2.

High‐field diffusion of electrons in silicon

With the time‐of‐flight technique we have measured the longitudinal diffusion coefficient of electrons in silicon at 300 K for fields from Ohmic up to 50 kV/cm. The results have been interpreted by means of Monte Carlo calculations with a theoretical model which includes the many‐valley (ellipsoidal and nonparabolic) structure of the band, acoustic intravalley, and several f and g intervalley scattering mechanisms.

Characterization of the Transport Properties of Halogen-Doped CdTe Used for Gamma-Ray Detectors

The mobilities, trapping times, activation energies, and trap concentration have been measured for both holes and electrons in Br and Cl-doped CdTe using the time-of-flight technique. Two electron traps 25 and 50 meV below the conduction band and two hole traps 140 and 350 meV above the valence band have been found. The 10 times larger concentration of levels found in the Br-doped CdTe can be explained using a model that describes the association of cadmium vacancies and substitutional halogens. The physical interpretation of the ??+ product when two levels are present is discussed for this case where the mobility is reduced and the lifetime is increased by trapping-detrapping phenomena. The measurements demonstrate that the material has excellent potential for ?-ray detectors that do not polarize with the proper surface preparation and make good detectors (6 keV FWHM for 122 keV ?-ray).

On the formation of Ni and Pt silicide first phase: The dominant role of reaction kinetics

4He+ backscattering spectrometry and x‐ray diffractometry have been used to study the formation of Ni and Pt silicides in Si(xtl)/M film structures with different metal film thicknesses ranging from 800 to 5000 A. Results clearly show that first the phase richer in metal (Ni2Si, Pt2Si) grows and continues to grow until all available metal is reacted, then the phase richer in Si (PtSi, NiSi) starts to grow. Present results prove that in Si(xtl)/Pt or Ni interactions the growth phase is determined by the reaction kinetics and that diffusion of metal atoms through Pt2Si and Ni2Si is fundamental in keeping the reaction going.

Self-compensation in CdTe

Abstract Using the time-of-flight technique, the drift mobilities, trapping levels, and trap concentrations were measured for both holes and electrons in Cl- and Br-doped CdTe grown by the Travelling Heater Method. Electron traps 25 and 50 MeV below the conduction band and hole traps 140 and 350 MeV above the valence band were found in Cl-doped material. The 25 MeV electron and 140 MeV hole traps were also found in the Br-doped CdTe, but with a concentration nearly 10 times that of the Cl-doped CdTe. A model based on the mass action approach of Kroeger which describes the association of cadmium vacancies and halogen atoms substitutionally located on tellurium sites has been used to interpret the different behavior of Br and Cl in CdTe. The stronger bonding of the Cl increases the tendency to form associates, thus decreasing the number of unassociated species (cadmium vacancies and isolated Cl) which act as trapping-centers in CdTe.

Hole mobility and Poole‐Frenkel effect in CdTe

We have performed, with the time‐of‐flight technique, an extensive investigation of the transport properties of holes in high‐resistivity CdTe as a function of temperature between 130 and 430 °K and for electric fields between 5 kV/cm and 50 kV/cm. In all investigated samples, at temperatures below 300 °K, the experimental hole mobility decreases on lowering either the temperature or the electric field. These features have been interpreted on the basis of the electric field effect on trapping and detrapping phenomena (Poole‐Frenkel effect) which cause a reduction of the mobility. A critical review of the existing theories of the Poole‐Frenkel effect is presented. The Poole‐Frenkel constant obtained by comparing the experimental data with the most reliable theories of the Poole‐Frenkel effect is in excellent agreement with its theoretical value. By analysis of the experimental data it was also possible to estimate the activation energy (Et=0.14 eV) and the concentration (NT=5×1016 cm−3) of the traps which ...