Beweglichkeitsanisotropie und Relaxation warmer Elektronen inn-Typ Germanium

The nonohmic part of the electric conductivity ofn-type germanium in a weak electric field depends on the field direction in the crystal. Measurements were made both with d.c. and microwave fields at lattice temperatures between 85 and 273° K. The anisotropy decreases with increasing field frequency and temperature. The data show that the effect of the effective mass anisotropy is enhanced by intervalley scattering. From the measured frequency dependence of the conductivity anisotropy the intervalley relaxation time is calculated and compared with results obtained from the acoustoelectric effect. In 〈001〉-direction where all 〈111〉-valleys of the conduction band are equally populated, the conductivity between 200 and 273° K is in accordance with theoretical results obtained byAdawi for an isotropic model; at lower temperature there are deviations even if ionized impurity scattering is included in the theory. The energy relaxation time is calculated from the measured frequency dependence of the 〈001〉-conductivity and compared with previous results.     

Energie-Relaxation warmer Ladungsträger in Germanium und Silizium

Experimental data on warm carrier energy relaxation times in germanium and silicon are reported. Measurements were done by the method of harmonic mixing of microwaves 1 in the temperature range between 77 and 200 °K. Relaxation times obtained forn-type germanium are in agreement with data reported byMorgan 2 as well as that ofSeeger 3 andGibson et al. 4. Measured energy relaxation times forp-type germanium as well as forn- andp-type silicon are reported here for the first time. A qualitative interpretation is given in terms of scattering by acoustic and optical phonons.     

The vacancy-interstitial pair in electron irradiated germanium

We have studied the influence of the nature and concentration of donor impurity on the 65°K and 35°K stages in electron irradiated n-type germanium. Because the nature of the impurity does not influence the 65°K stage and because this stage is present alone in lightly doped samples, we confirm that it is associated with the annihilation of a vacancy-interstitial pair. Because the 35°K stage is directly connected to the impurity concentration, and not to the free electron concentration, we conclude that it is associated with the annihilation of a vacancy and interstitial-impurity pair. We have shown that the annihilation of the vacancy-interstitial pair occurs through the interstitial mobility at 65°K, 27°K and 4.5°K depending on its charge state, and that the interstitial-impurity mobility occurs at 35°K.

Our model explains easily the radiation annealing, the behavior of irradiated p-type germanium and can be extended to the case of indium antimonide and perhaps of silicon.     

Quantum oscillations in p-type inversion layers of (111) and (100) silicon field effect transistors

For the first time Shubnikov-de Haas oscillations have been observed in p-type inversion layers of (111) and (100) silicon field effect transistors. For both orientations a single electric subband was found. The effective mass of the surface carriers was determined from the temperature dependence of the oscillations, for (111) surfaces as a function of the surface electric field. At low gate voltages spin splitting of the Landau levels was resolved.     

Shubnikov-de Haas oscillations in p-type inversion layers on n-type silicon

Surface Shubnikov-de Haas oscillations have been measured in p-type channels of (110) silicon field effect transitors between 1.4 and 4.2 K in magnetic fields up to 10 Tesla. Two electric subbands were revealed and the effective masses of the holes in both bands could be determined. For one subband the dependence of the mass on the surface electric field was investigated. At low gate voltages the g-factor of the holes was measured from the spin splitting of the Landau-levels.     

Crystal electric field next to a hydrogen-like interstitial— µ+ in PrNi5

Muon spin rotation measurements of the temperature dependence and the anisotropy of the μ⁺ Knight shift in single crystals of the crystal electric field singlet ground state system PrNi₅ reveal pronounced deviations from a linear scaling of the Knight shift with the bulk magnetic susceptibility atT≤50 K. They are explained by a μ⁺ induced modification of the atomic susceptibility of neighboring Pr³⁺ ions. From the Knight shift anisotropy atT> 50 K it is determined that the implanted μ⁺ occupy a single intersitial site, namely the 6i site (0.5, 0, 0.21±0.02). Using this site information, good model fits to the measured data are obtained assuming a μ⁺ induced perturbation of the crystal electric field at the Pr³⁺ ions next to the μ⁺. Apparently, the presence of the μ⁺ leads to a lowering of the local symmetry, causing a lifting of the degeneracy and a pronounced rearrangement of the low lying crystal electric field levels for these ions.     

Lifetime spectra of positrons in deformed Ge

Positron lifetime measurements have been performed inn-type andp-type germanium single crystals deformed by compression. The results are compared with those of deformed GaAs single crystals obtained by the authors previously. In bothn andp-type germanium the lifetime τ₁ and its intensityI ₁ decreased with deformation. Using the trapping model, the trapping rates of positrons by dislocations are obtained, which in turn gave the cross width of the dislocation as 20.0 Å and 8.2 Å forn-type andp-type germanium, respectively. In terms of Read's model the fraction of the dangling bonds occupied by electrons is obtained to 0.26 in then-type germanium. This value was smaller than those obtained forn-type GaAs, i.e., 0.46 and 0.50 for Ga- and As-dislocation, respectively. It is found that doping causes the trapping of positrons. Inp-type germanium the fractionf was determined to 0.25 in terms of Schröter and Labusch's model.     

Influence of the linear k term on the shape of the isoenergetic surfaces in p-type GaSb,deduced from galvanomagnetic measurements

From transverse or longitudinal magnetoresistance and Hall coefficient measurements performed on three samples cut in a single crystal of p-type GaSb along selected crystallographic directions, we derive six equations involving the geometric parameters of the isoenergetic surfaces. The generally admitted valence band model for GaSb is the nonquadratic model proposed by Lax and Mavroides in the case of Germanium and Silicon. We find that this model cannot account simultaneously for all the galvanomagnetic phenomena observed on p-type GaSb, in particular for the longitudinal magnetoresistance.The existence of a linear k term in the enery expression lifts the degeneracy so that the energy maxima of the valence band are not at k (000). We show then that, at 77°K, the difference between the level of the valence band maxima and the value of the energy at k (000) may be large enough to consider the existence of a multiellipsoidal structure. This structure accounts for all the observed galvanomagentic phenomena.The ellipsoids are found along (100) and (111) directions for light and heavy holes respectively. We calculate the corresponding anisotropy coefficients: K₂=1·66 and K₁=3.     

Beweglichkeitsanisotropie warmer Elektronen in n-Typ Germanium bei 35 GHz

The field dependent electric conductivity has been investigated withn-type germanium crystals of various orientations using microwaves of a frequency of 35 Gc/s. The orientation effect yields values ofSchmidt-Tiedemann's constantsβ ₀ andγ ₀. The ratioγ ₀/(?β ₀) is nearly independent of the lattice temperature with an average value of 0·65 in the temperature range between 100 and 273° K.     

Properties of erbium silicate doped with chromium in porous silicon

The possible formation of chromium-doped erbium silicate Er₂SiO₅: Cr in thin layers of porous silicon is demonstrated. This paper reports on studies of the photoluminescence, electron paramagnetic resonance, and transverse current transport in porous silicon layers (with different chromium and erbium contents) grown on n-and p-silicon single crystals heavily doped with shallow impurities. The Er₂SiO₅: Cr phase with the photoluminescence maxima at approximately 1.3 and 1.5 μm manifests itself after high-temperature annealing at 1000°C. The introduction of erbium and annealing at 700°C increase the intensity of the red photoluminescence of porous silicon by several factors. The decrease in the electrical conductivity of porous silicon suggests the onset of the formation of erbium silicate. The current-voltage characteristics exhibit a nonlinear behavior with an exponential dependence of the current on the voltage due to the discrete electron tunneling. An electron paramagnetic resonance spectrum of P _b centers in p-type heavily doped silicon is observed for the first time.     

Irradiation-induced compensation of n-type germanium — electrical measurements

The temperature dependence of the Hall effect in an n-type germanium sample following each of a series of 2 MeV electron irradiations at 80 K has been analysed. It is shown that conversion to p-type proceeds by the introduction of defects which are acceptors contrary to the suggestion made recently that conversion proceeds by the removal of donors.     

Hot́ hole anisotropic effect in silicon and germanium

Anisotropic effect of the hole drift velocity in silicon and germanium has been investigated with the time of flight technique by applying the electric field parallel to the <100 and <111 crystallographic axis. The measurements were performed for electric fields ranging from 10 to 3 × 10⁴V/cm and temperatures from 40 to 200°K. The results indicate that the anisotropic effect v_d<100/v_d<111 increases with decreasing temperature and increasing electric field, and reaches a saturation value at high electric fields (? 10⁴V/cm). The maximum anisotropic effect for Ge is 1.25 at 40°K and for Si is 1.2 at 45°K. A qualitative analysis of the experimental data indicates that the anisotropic effect is due to the warped heavy-valence-band shape.     

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.     

Temperaturabhängigkeit der Austrittsarbeit von Silizium

The temperature dependence of the work function of silicon was measured in ultra high vacuum between room temperature and 1000°K by means of the temperature dependent contact potential between the silicon surface and a metal reference with the Kelvin method. We have investigated both (111)-surfaces of p-type silicon, cleaned by heating in vacuum, and cleaved surfaces of different doping. For stable surfaces, temperature coefficients between 0 and +1·10^?4 eV/°K are found. Neither doping nor the transition of electrical conductivity from extrinsic to intrinsic has significant influence. This is due to the high density of surface states near the Fermi-energy. Freshly cleaved surfaces are unstable; when first heated up, an irreversible behaviour of the work function is observed, which gives some information concerning the surface states. From our measurements one can also roughly deduce the temperature dependence of the electron affinity. Finally, changes of the temperature dependence of the work function caused by contamination of the surface were investigated.     

Evidences of p-type conductivity in iodine grown gallium selenide

Photoconductivity, photovoltage and photoelectromagnetic effect have been studied at different excitation intensities between 80 and 300°K in GaSe grown by the iodine transport method. The experimental results give evidence that the conductivity of these samples, which are n-type at room temperature, changes to p-type at low temperature.     

Changes in the parameters of <Emphasis Type="Italic">p</Emphasis>-Ge compression curves for various methods of plastic deformation

The behavioral features of deformation characteristics are investigated in p-type germanium single crystals under the combined action of electric current and temperature and separate exposure to electric current. The p-Ge resistivity decreases with increasing strain. When temperature and electric current jointly act on the single crystal, it is revealed that the resistance to deformation increases. In the case where only the electric current affects the compressed single crystal, there is enhancement in the plastic properties. Different deformation methods qualitatively affect the shape and parameters of curves. The surface microstructures of prepared deformed samples are studied. Possible physical explanations for the observed phenomena are proposed.     

Scattering mechanisms in p-type GaSb in the temperature range 30–300°K

In a former paper[1], we have shown that the magnetoresistance coefficient in p-type GaSb (1+ξ) remains close to 1 at 77°K and that the mobilities ratio remains equal to 6 in the temperature range 77–300°K.We show from these results that between 30 and 300°K, the predominant scattering is a mixed scattering by lattice vibrations and ionized impurities. Interband scattering is the predominant process for light holes, while heavy holes undergo intraband scattering. In this temperature range, this mechanism accounts for the mobility variation, a result which had not been found so far on p-type GaSb.     

Interference effects in the electrical conductivity tensors of doped polar semiconductors

In this paper, we develop a general procedure, based on the Kubo formula, for finding the frequency- and wavevector-dependent electrical conductivity tensor for arbitrary polarizations of the applied electric field. This procedure gives careful consideration to both the electron and the ion contributions to the current density. We find that, in addition to the standard electron and ion contributions to the conductivity tensor, there are contributions arising from the quantum interference between the electrons and the ions. These interference effects, which will affect the infrared absorption of a material, are similar to the interference effects observed by Cerdeira, Fjeldly, and Cardona (Solid State Commun.13 (1973), 325–328; Phys. Rev. B8 (1973), 4734–4745; 9 (1974), 4344–4350) in Raman scattering from p-type Si. We then evaluate these cross terms for simple models of a variety of semiconductors. We find that these interference effects are finite-q effects, with the actual dependence of the cross terms on the wavevector q being sensitive to the symmetry of the crystal. We also find that, in principle, these cross terms may be quite large near the TO-phonon frequency ω_TO. The cross terms are evaluated for both n-type and p-type semiconductors, and it is suggested that they are probably most important for p-type materials. However, we also find that the basic structure of these terms is very similar in the two cases.     

Conductivity anisotropy ofn-type silicon in the range of warm and hot carriers

The electric conductivity ofn-type silicon was measured as a function of the field intensity in different crystallographic directions at temperatures between 78 and 275 °K. From the data at medium fields (range of warm carriers) the coefficientsβ ₀ andγ ₀ ofSchmidt-Tiedemann's anisotropy theory were determined. Especially at low temperatures these coefficients are different for lightly and heavily doped crystals. The differences can be explained by the influence of ionized impurity scattering in addition to lattice scattering. The repopulation of the energy valleys of the conduction band as a function of the field intensity was calculated from the ratioγ ₀/β ₀ and — in the range of hot carriers — from the conductivities measured in <001> and <111> directions. A maximum increase of population of a cool valley was found to be between 0.5 and 1.2 of the zero-field population, depending on the particular sample, the field intensity being about 0.5 kV/cm and the lattice temperature 89 °K.     

Generation of far-infrared radiation by hot holes in germanium and silicon inE ⊥H fields

The experimental results obtained by the investigation of stimulated FIR emission from dopedp-type germanium andp-type silicon by hot holes in crossedE andH fields at = 10 and 80 K are reported. The analysis of the emission intensity fromp-type germanium as a function ofE andH fields permits us to draw a conclusion about the important role of quantization of the energy spectrum of light holes and the contribution of light hole transitions with n = 2 to the amplification of FIR radiation. A new region of generation is demonstrated inp-type germanium under uniaxial stress. The first experimental results on stimulated FIR emission fromp-type silicon are reported.