Spin-dependent photoconductivity in n-type and p-type amorphous silicon

It is found that, as in crystalline silicon, the photoconductivity in amorphous silicon prepared by glow discharge is strongly spin-dependent. In this material, the position of the Fermi level can be smoothly varied by phosphorous or boron doping and the magnitude of the spin-dependent recombination has been measured as a function of the doping: it is found to have a large maximum when the material is intrinsic. The similarities with the spin-dependent effects in crystalline and dislocation silicon suggest that the recombination process in amorphous silicon is the same as in the crystalline material and that dislocation-like centres are responsible for the spin-dependent recombination properties in both materials.     

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.     

Photoelectronic characterization of n-type silicon wafers using photocarrier radiometry

Photocarrier radiometry (PCR) was used to characterize four n-type silicon wafers with different resistivity values in the 1-20 Ω cm range. Simulations of the PCR signal have been performed to study the influence of the recombination lifetime and front surface recombination velocity on them; besides, the transport parameters (carrier recombination lifetime, diffusion coefficient, and frontal surface recombination) of the wafers were obtained by means of a fitting procedure. The PCR images that are related to the lifetime are presented, and the first photoelectronic images of a porous silicon sample are obtained.     

An infra-red study of defects produced in n-type silicon by electron irradiation at low temperatures

The infra-red local mode absorption produced by irradiation of n-type silicon by 2 MeV electrons at temperatures in the range 100–140°K has been investigated. A new band at 884 cm^-1 has been observed and interpreted as due to a vacancy— oxygen complex (A-centre) with a trapped electron.     

On the g factor for electrons in n-type silicon surface inversion layers

Self-consistent calculations for energy levels are performed for n-type inversion layers of silicon with magnetic field perpendicular to the (100) surface. ‘Apparent’ g factor g¹, obtained from the period of oscillation of states density at Fermi level for varying magnetic field, is plotted as a function of the $\text{Γ}\text{2βH}$, where Γ is the width of Landau levels. The results show that $\text{g}{}^1\text{～ g}\text{for Γ ? 2β}\text{H,}\text{and}\text{g}{}^1\text{～}\text{5 for Γ < 2β}\text{H}$. This means that we should be very careful when interpret the g shift of electrons in inversion layers for small surface electron density.     

Valley splitting and valley degeneracy in n-type silicon (110) inversion layers

The magneto-quantum transport phenomena of silicon (110) n-type inversion layers directly reveal the presence of two types of electrons in i = O and O' electric subband states from their respective quantum oscillations. While the higher i = O' states are occupied by only about 6% of the total electron concentration in our samples, the i = O electrons populate two valley pairs each, the level ladders of which are shifted in energy by less than the Landau splitting in the range where quantum oscillations are observed. We propose this effect to originate from a slight misorientation (Δθ < 0.5°) of the surfaces investigated with respect to the (110) axis. Hence, increasing the gate voltage in a quantizing magnetic field all four i = O valleys are alternatingly occupied in pairs with increasing Landau quantum number in our (110) surfaces contrary to former conclusions on samples with comparable properties. The effect of the magnitude of Δθ on the resulting magneto-quantum oscillations is unimportant for 0 < Δθ ? 0.5° as a result of energy minimization for the total electron system.     

Transport parameters of n-type GaSb

The conduction band parameters of GaSb have been investigated in the temperature region 70–280 K. Hall and magnetoresistance data have been analysed according to the two band model to obtain information about the energy separation ΔE₁₂ of the conduction band minima and its temperature coefficient α₂.     

Thermally-induced changes in barrier heights of aluminium contacts to p- and n-type silicon

The barrier height of aluminium contacts to n-type silicon, φ_bn, increases continuously from ～-0.45 eV to ～-0.80 eV as a result of post-evaporation heat treatments in the range 100–550°C. Aluminium-p-type silicon contacts show complementary behaviour, with φ_bp progressively decreasing from ～-0.75 eV to ?0.40 eV over this same temperature range. Three mechanisms are believed to contribute to this behaviour.     

Frequency shift of the plasma reflectivity minimum due to uniaxial stress in n-type silicon

The pronounced influence of 〈100〉 compressive stress on the frequency of the reflectivity minimum associated with free carrier dispersion has been measured for radiation polarized perpendicular or parallel to stress. Interpretation of the results in terms of the electron transfer model suggests that the phenomenon might be used to determine effective mass anisotropies in multivalley semiconductors.     

Impact of ZnTe buffer on the electrical properties of n-type GaSb:Te films

We have investigated on the molecular beam epitaxy (MBE) of Te-doped GaSb films on ZnTe buffer. Te-doped GaSb (GaSb:Te) films with and without ZnTe buffer were grown on (0 0 1) GaAs substrates. GaSb:Te/ZnTe/GaAs film revealed higher mobility (=631 cm²/V s) in comparison to GaSb:Te/GaAs film (=249 cm²/V s). To explain the higher mobility of GaSb:Te on ZnTe buffer, dislocation density and temperature dependence of Hall measurement results were analyzed. Temperature dependence of Hall measurement shows strong influence of the dislocation scattering, which indicates that dislocation reduction by the ZnTe buffer enhances the carrier mobility of GaSb films.     

Temperature dependence of the energy separation between Γ and L minima in n-type GaSb

Energy separation ΔE_c between Λ and L minima of GaSb conduction band is deduced from temperature dependence of tunneling current in p−n junctions. ΔE_c is found to inceasing vx. temperature with a coefficient d(ΔE_c/dT) of about - 2.10^-4eV/dgK.     

Electrical properties of n-type GaS single crystals

Hall effect and Thermally Stimulated Currents (TSC) measurements have been carried out with the current flowing perpendicular to the c-axis on n-GaS crystals grown both from the melt by the Bridgman-Stockbarger method and from the vapour by chemical transport with iodine. An impurity hopping conduction with an activation energy of 0.2 eV has been evidenced in the range of temperatures between 200 and 300 K. The results of TSC measurements indicate the iodine as being responsible for a donor level at 0.44 eV from the conduction band.     

Electrical properties of n-type vapor-grown gallium nitride

Hall measurements are reported for undoped and Zn-doped vapor-grown single crystal GaN on (0001) Al₂O₃ layers with 298 K carrier concentrations (n-type) between 1·4×10¹⁷cm^?3 and 9×10¹⁹ cm^?3. Then n～10¹⁷ cm^?3 crystals (undoped) have mobilities up to μ～440 cm²/V sec at 298 K. Their conduction behavior can be described by a two-donor model between 150 and 1225 K and by impurity band transport below 150 K. Crystals with n≥8×10¹⁸ cm^?3 show metallic conduction with no appreciable variation in n or μ between 10 and 298 K.Results of mass spectrographic analyses indicate that the total level of impurities detected is too low to account for the observed electron concentration at the n～10¹⁹ cm^?3 level, and suggest the presence of a high concentration of native donors in these crystals. No significant reduction in carrier concentration was achieved with Zn doping up to concentrations of ～10²⁰ cm^?3 under the growth conditions of the present work, and no evidence was found to indicate that high conductivity p-type behavior may be achieved in GaN. The influence of factors such as growth rate, crystalline perfection and vapor phase composition during growth on the properties of the layers is described.     

Spin relaxation of conduction electrons in highly-doped n-type germanium at low temperature

We present a theory of the spin relaxation time of the conduction electrons in highly-doped n-type germanium at liquid helium temperature. The theory is compared with some of our measurements and the experimental data available in the literature on As-doped germanium. The observed linewidth at T = 10 K is accounted for in the whole metallic concentration range (N_D > 3 × 10¹⁷cm^?3).In the lower concentration range (3 × 10¹⁷ < N_D < 10¹⁸cm^?3), the relevant mechanism is the random jumping of the g factor upon intervalley scattering. The agreement with experiment is good without any adjustable parameter.In the higher concentration range (N_D > 10¹⁸cm^?3), the dominant process for the linewidth is the spin-flip scattering by ionized donors (Elliott process); the usual theory is shown to be insufficient and the greater effectiveness of scattering by the localized part of the donor potentials is pointed out. The calculated linewidth is related to the intervalley scattering time T_iv. The agreement with experiment is good and predictions are given for the linewidth in the case of other shallow donors in the same concentration range.     

Optical characterization of doped and undoped GaAs at 300 K

Infrared reflectance spectroscopy was employed for the optical characterization of undoped GaAs, as well as for GaAs doped with Si, Zn and Cr. Dielectric constants, refractive indices and extinction coefficients were determined using the classical two oscillator model.     

Transport properties of conduction electrons in n-type inversion layers in (100) surfaces of silicon

The conductivities of n-type inversion layers in (100) surfaces of p-type silicon were measured extensively as functions of electron density in the inversion layer, the ambient temperature and the applied magnetic field. Measurements were made on the carefully fabricated four “classes” of MOS field-effect transistors whose maximum mobilities at 4·2K were 14,000, 8000, 6800 and 1500 cm²/V·sec, respectively. From the temperature dependence of the mobility, dominant momentum scattering was reasonably ascribed to surfon at 100 ～ 300 K. and degenerate or non-degenerate coulomb scattering at lower temperatures as treated by Stern and Howard. From the curves of conductivity vs temperature at low temperatures and low electron concentration for specimens with high mobilities, an activation energy of 1·2 meV, relating to the shallow bound states associated with the lowest electrin sub-band, was observed. The conductivity σ_xx of the inversion layer in a strong transverse magnetic field showed behaviors like those of completely free electrons without effects belonging to its material in its oscillation pattern. That is, the peak value of σ_xx as a function of the gate voltage V_R dependend only on the Landau index. The σ_xx as a function of the magnetic field H at a constant V_R showed a similar Shubnikov-de Haas (SdH) type oscillation to that of three dimensional one. The SdH oscillation gave an “apparent” g-value g* which ranges from 2 to 5 depending on the surface carrier density n_s, due to the change in the ratios of the widths of the Landau levels to the level separation. The “reasonable” g-value of the conduction electrons in the inversion layer has been determined using a modified tilted magnetic field method. The g-value at the fixed magnetic field was independent of surface carrier density n_s and tended to 2 in the extreme strong magnetic field.Discussion is made of the g-value relating to the Landau level width and the energy gaps in the density of states under strong magnetic field.     

Quantum efficiency and radiative lifetime in degenerate n-type GaAs

The hole lifetime, the radiative lifetime, the non-radiative lifetime, and the internal quantum efficiency in degenerate n-type GaAs crystals have been investigated with a simplified model of degenerate semiconductors, in which the recombination constant B is approximately proportional to the$\text{?13}\text{8}$ power of the electron density.In n-type GaAs at 77 K, the radiative lifetime reaches a minimum equal to 4 × 10^?9 sec. at 6 × 10¹⁷ cm^?3, and the internal quantum efficiency exhibits a maximum equal to 50% at 8 × 10¹⁷cm^?3, in good agreement with the theoretical prediction of Dumke and the experiments of Cusano. At high impurity concentrations, the polytropy effect is taken into account in the case of GaAs crystals doped with tellurium and selenium. Finally, it is suggested that, for a given high concentration, the internal quantum efficiency increases with increasing temperature, in accordance with the observed results.     

Multiphoton electronic-spin generation and transmission spectroscopy in n-type GaAs

Multiphoton electronic-spin generation in semiconductors was investigated using differential transmission spectroscopy. The generation of the electronic spins in the semiconductor samples were achieved by multiphoton pumping with circularly polarized light beam and was probed by the spin-resolved transmission of the samples. The electronic spin-polarization of conduction band was estimated and was found to depend on the delay of the probe beam, temperature as well as on the multiphoton pumping energy. The temperature dependence showed a decrease of the spin-polarization with increasing temperature. The electronic spin-polarization was found to depolarize rapidly for multiphoton pumping energy larger than the energy gap of the split-off band to the conduction band. The results were compared with those obtained in one-photon pumping, which shows that an enhancement of the electronic spin-polarization was achieved in multiphoton pumping. The findings resulting from this investigation might have potential applications in opto-spintronics, where the generation of highly polarized electronic spins is required.     

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.     

Low-temperature chemical vapor deposition of highly doped n-type epitaxial Si at high growth rate

We investigated the growth of in-situ n-type doped epitaxial Si layers with arsenic and phosphorus by means of low-temperature chemical vapor deposition using trisilane as Si-precursor. Indeed, in order to prevent the alteration of the characteristics of the devices which are already present on the wafer, an epitaxy process at low temperature is highly desired for applications such as BiCMOS. In this work, the varying parameters are the deposition temperature, the Si-precursor mass flow and the dopant gas flow. As a result, a process for the deposition of heavily doped epilayers was demonstrated at 600 °C with high deposition rate, which is important for maintaining high throughput and low process cost. We showed that using trisilane as a Si-precursor resulted in a much more linear n-type doping behavior than using dichlorosilane. Therefore it allowed an easier process control and a wider dynamic doping range. Our process is an interesting route for the epitaxy of a low-resistance emitter layer for bipolar transistor application.