Opto-electronic properties of CuAlO2

CuAlCO₂ is a p-type semiconductor with an average hole mobility of $\text{1.1 × 10}{}^{\mathrm{?7}}\text{m}{}^2\text{Vs}$. From photoelectrochemical measurements its bandgap is found to be indirect allowed at 1.65 eV; other interband transitions are at 2.3 and 3.5 eV. The valence band is made up mainly from Cu-3d wave functions and lies 5.2 eV below the vacuum level.     

Magnetophonon oscilation of thermoelectric power in the conduction band of tellurium

At about 200K where the Hall coefficient of p-Te reverses its sign, magnetophonon oscillation of electron in the conduction band was observed for the first time in H6c and H⊥c. It was attained by measuring the second derivative of the longitudinal magneto-Seebeck coefficient (?²α₆/?H²). It is found to be explained fairly well by a simple parabolic band model even for H6c. Effective mass values of the conduction band at 200K are deduced on an interpretation; $\text{m}{}^1{}_{\mathrm{\perp }}\text{=0.160m}{}_0$ and $\text{m}{}^1{}_6\text{= 0.072m}{}_0$. Rather large contribution of electron in ?²α₆/?H² may be due to the enhanced electron diffusion in a transition region from p-type to intrinsic as reported recently in p-InSb. This interpretation is supported also by the oscillation of longitudinal magnetoresistance (?²?₆/?H²) which was observed for H6c.     

Phenomenological predictions of the SO(10) supersymmetric grand unified model

The phenomenological predictions of the SO(10) supersymmetric grand unified model (SO(10) SGUM) for the mass scales M₁, M₂, weak angle ifsin²θ_w, quark-leptons mass ratios $\text{m}{}_{\mathrm{<mtext>b</mtext>}}\text{m}{}_{\mathrm{\tau }}$, $\text{m}{}_{\mathrm{t}}\text{m}{}_{\mathrm{<mtext>b</mtext>}}$, $\text{m}{}_{\mathrm{\tau }}\text{m}{}_{\mathrm{\nu }}{}_{\mathrm{\tau }}$ and proton lifetime τ_p are estimated by using renormalization group analysis at one-loop level. In contrast with SU(5) SGUM, we find that the SO(10) SGUM still has problems with τ_p but not with sin²θ_w and $\text{m}{}_{\mathrm{<mtext>b</mtext>}}\text{m}{}_{\mathrm{\tau }}$, which may suggest that supersymmetry would be bro at a mass scale $\text{?10}{}^7\text{GeV}$.     

X- ray photoemission study of the interaction of oxygen and air with clean cobalt surfaces

The interaction of oxygen with polycrystalline cobalt surfaces has been studied at 300 K (1 × 10^?6 to 1 × 10^?5 Torr) using high-resolution (monochromatized) X-ray photoemission. At high exposures (> 100 L nominal) CoO is identified as the product from the nature of the $\text{Co}\text{2}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{, 2}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{, 3}\text{s}$, and valence band spectra. There is no evidence for measurable amounts of Co₃O₄ or Co₂O₃. Two O 1s features are observed at both high and low (10L) exposures. The dominant O 1s feature at 529.5 ± 0.2 eV corresponds to the oxide and a minor feature at 531.3 ± 0.2 eV is attributed to non-stoichiometric surface oxygen. Exposure to air produces quite different results, with a dominant O 1s feature at 531.5 ± 0.2 eV and dominant $\text{Co}\text{2}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{2}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ features centered at 781.3 ± 0.2 eV and 797.1 ± 0.2 eV. These three values are very close to those reported here for bulk Co(OH)₂. Ion etching of the air-exposed surface removes this dominant surface product rapidly revealing some oxide and finally metal.     

Photoconductivity and photovoltaic excitation spectra and their wavelength derivative in Cu2O

Photoconductivity and photovoltaic excitation spectra, both direct and wavelength modulated, have been performed on monocrystalline Cu₂O from 6 to 300K. At low temperatures both types of direct spectra exhibit the excitonic structures already observed by other techniques such as absorption and reflectivity. The wavelength-modulated PC spectra reveal additional structures and in particular well-defined oscillations in the green fundamental continuum, related to photocarrier LO phonon interactions. The analysis of these results shows that the 149cm^?1 (18.5 meV) LO phonon is responsible for the observed periodic structures. The values found for the energy of the collector level (2.305 ±0.001 eV) and for the effective mass ratio $\text{(}\text{m}{}_{\mathrm{h}}\text{m}{}_{\mathrm{e}}\text{bsime; 12)}$, indicate that the oscillations are produced by the electrons excited from the heavy hole valence band Γ₈⁺ to the Γ₁⁺ conduction band. A study of the position and of the contrast of the phonon oscillations as functions of temperature illustrates the behaviour of the gap displacement with changes in temperature and throws some light onto the mechanisms responsible for the existence of such oscillations.     

Electrical properties of narrow gap semiconductor PtSb2

Results of measurements of conductivity, Hall and Seebeck coefficients of tellurium doped n-type crystals of platinum antimonide are presented. The Hall coefficient and the Seebeck coefficient undergo sign inversion twice, below and above room temperature. The detailed analysis of the experimental results revealed that below 200 K PtSb₂ can be described by a simple conduction and valence band model. The energy gap E_g = (110?0.15 × T) (meV), the electron conductivity mass m_n^c/m₀ = 0.35, acoustic phonon limited electron mobility 〈μ_a〉_n = 3 × 10⁶ T^{?$\text{3}\text{2}$} ($\text{cm}{}^2\text{V · s}$) and mobility ratio 〈μ_a〉_n/〈μ_a〉_p = 0.4 are determined. However, at higher temperatures a more complicated valence band model is needed to account for the experimental results. The arguments for the existence of subsidiary valleys in the valence band are presented.     

Hole mobility in p-type HgTe

Experimental data concerning the electrical conduction and Hall coefficient in HgTe samples with acceptor states have been collected and analysed. In the analysis three ranges of acceptor concentration have been distinguished: a low concentration range up to about 5 × 10¹⁵ cm^?3 (pure samples), a high concentration range from 10¹⁶ to 10¹⁸ cm^?3 (p-like samples), and an extremely high concentration range above 10¹⁸ cm^?3 (p-type samples). In pure HgTe samples the holes are in the valence band, in p-like samples the “holes” are in the impurity band, and in p-type HgTe samples the holes are in a strong mixing impurity-valence band. The mobility of holes in the valence band is of the order of $\text{10}{}^5\text{cm}{}^2\text{Vs}$. The mobility of “holes” in the impurity band decreases with increasing impurity concentration from about $\text{5 × 10}{}^3\text{cm}{}^2\text{Vs}$ to $\text{125}\text{cm}{}^2\text{Vs}$. The mobility of holes in p-type HgTe samples is independent of the acceptor concentration and is equal to $\text{125}\text{cm}{}^2\text{Vs}$.     

Hole contribution to the elastic constants of SnTe

Ultrasonic wave velocities have been measured in SnTe single crystals with hole concentrations of 1.0 and 4.5 × 10²⁰/cm³. The shear elastic stiffness constant C₄₄ is sensitive to the hole concentration but $\text{1}\text{2}\text{(C}{}_{11}\text{? C}{}_{12}\text{)}$ is not, a result which is consistent with the valence band pockets being sited at the L points. The non-ellipsoidal, non-parabolic multivalley band model has been used to calculate the hole contribution to the elastic constants. The calculated difference between the shear constant C₄₄ (2.78 × 10¹⁰ dyne cm^-2) for the two crystals is in agreement with that measured experimentally (2.67 × 10¹⁰ dyne cm^-2). The shear deformation potential constant E_u for the SnTe valence band is 7.8 eV at 293°K.     

Determination of the deformation potential of shallow donors in silicon

The stress dependence of the energy of the ground state of group V impurities (P, Sb) in silicon was investigated by measurement of the Hall effect in a wide range of pressures. A conclusion was reached that the deformation potential of the lowest impurity state of shallow donors (Ξ¹_u) in silicon differs from the deformation potential of the conduction band (Ξ_u), the value of this difference being dependent on the type of the impurity. According to our data, the most probable values for ($\text{Ξ}{}_{\mathrm{u}}\text{ Ξ}{}^1{}_{\mathrm{u}}$) are 0.12 eV for phosphorous-doped silicon and 0.06 eV for antimony-doped silicon.     

Core-level reflectance spectroscopy of germanium by means of synchrotron radiation

Reflectance spectra due to 3d core-levels of Ge have been measured in the photon-energy region from 29 to 38 eV by means of synchrotron radiation. Second-energy-derivative spectra have newly shown pairs of doublet structures with energy separation of the Ge $\text{3d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{?}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ core-level splitting. The observed doublet structures are assigned to the transitions from the $\text{3d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ and $\text{3d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ core-levels to the flat regions of the conduction band around the particular symmetry points of Δ₆^c and L(₃^c(L₆^c, L_4,5^c).     

Luminescence above the gap in heavily Zn-doped GaAs

Several distinct features have been observed in the photoluminescence spectrum of heavily Zn-doped GaAs, in the range between 1.65eV to 2.25eV. They are attributed to direct recombination across the E_o+?_o gap and to indirect processes related to X^c₁ and X^c₃. The X^c₁ minima are thus located to be 1.935±0.01eV above the top of the valence band at 100K. Their shear deformation potential $\text{E}$^X₂ is found to be $\text{E}{}^{\mathrm{X}}{}_2\text{=5.5±2eV}$.     

Valence band photoemission spectroscopy of a ternary layered semiconductor: ZnIn2S4

UV photoemission spectroscopy (UPS) experiments have been carried out on the layer compound ZnIn₂S₄ employing several different photon energies in the range $\text{h}\text{?}{}_{\mathrm{\omega }}\text{= 9.5?21.2}\text{eV}$. The energy distribution curves (EDC's) exhibit four valence band density of states structures besides the Zn 3d peak. These five peaks appear 0.90 eV, 1.6 eV, 4.3 eV, 5.8 eV and 8.7 eV respectively below the top of the valence band, E_v. The atomic orbital character of the shallowest peak A appears different from that of the three deeper valence band peaks B, C and D and this is discussed in terms of the more or less pronounced ionic character of the intralayer chemical bonds. These results demonstrate that an overall understanding of the electronic states in complex structures can be achieved by an approach based on photoemission experiments and chemical bonding considerations which has been widely used in the past to study simple binary layer compounds.     

Total width of the lowest T = 2 state in 24Mg

By analyzing thick-target excitation functions of the $\text{E}{}_{\mathrm{<mtext>p</mtext>}}\text{= 3906}\text{keV}{}^{23}\text{Na}\text{(}\text{p}\text{, γ)}$ resonance we have determined Γ_c.m ≦ 530⁺⁴⁰_?70 eV for the width of the lowest T = 2 state of ²⁴Mg. The beam energy resolution function was measured using a narrow ²⁷Al(p, γ) resonance at E_p = 3671 keV, for which we obtain Γ_c.m. = 180 ±50 eV.     

Lepton mixing and neutrino oscillations

The present article is a review of phenomena connected with neutrino oscillations. Mixing of two neutrinos (Majorana as well as Dirac) with masses m₁ and m₂ is considered in detail. It is shown that the hypothesis of lepton mixing is not in contradiction with the existing data if |m₁²?m₂²| ? 1 (eV)². Possible experiments designed to reveal neutrino oscillations at reactor, meson factory and high energy accelerator facilities are considered. In such experiments oscillation might be found if $\text{|m}{}_1{}^2\text{?m}{}_2{}^2\text{| ? 0.01}\text{(eV)}{}^2$. The possibilities of searching for oscillations by experiments on cosmic ray neutrinos and especially on solar neutrinos are discussed in detail. The last experiments have an incredible high sensitivity from the point of view of testing the lepton mixing hypothesis (oscillation effects might be observable if $\text{|m}{}_1{}^2\text{?m}{}_2{}^2\text{| ? 10}{}^{\mathrm{?12}}\text{(eV)}{}^2$). The “solar neutrino puzzle” is also discussed from the point of view of lepton mixing. Neutrino oscillations are considered then in the case where in nature there exist N ? 2 neutrino types.In conclusion the case of heavy lepton mixing is considered. It is shown that in a concrete scheme with right-handed currents, the probabilities of such processes as μ → eγ, μ → 3e etc. can be close to existing experimental upper limits, provided the heavy lepton masses are of an order of a few GeV, whereas the probabilities of the above processes are entirely negligible if only neutrinos are mixed.     

Optical detection of cyclotron resonance of electron and holes in CdTe

Cyclotron resonance of electron and holes have been optically detected at 70 GHz and at 1.8 K in n-type CdTe. The bare effective masses, in unit of the free electron mass, are found to be: $\text{m}{}^1\text{= 0.088 ± 0.004}$, $\text{m}{}^1{}_{\mathrm{lh}}\text{= 0.12 ± 0.01}$, $\text{m}{}^1\text{= 0.60 ± for H // <100>}$, and $\text{m}{}^1{}_{\mathrm{e}}\text{= 0.089 0.004}$, $\text{m}{}^1{}_{\mathrm{lh}}\text{= 0.11 ± 0.01}$, $\text{m}{}^1{}_{\mathrm{hh}}\text{= 0.69 ± 0.02}$ for H // <111>. The Luttinger valence band parameters deduced from these measurements are: γ₁ = 5.3 ± 0.5, γ₂ = 1.7 ± 0.3 and γ₃ = 2.0 ± 0.3, in fair agreement with the calculations of Lawaetz.     

High-resolution proton scattering on 46Ti

Differential cross sections were measured for ⁴⁶Ti(p, p) and ⁴⁶Ti(p, p₁) at four angles between E_p = 1.5 and 3.1 MeV, with an overall energy resolution of about 300 eV. Spins, parities, total and partial widths were extracted for 144 resonances. Six analogue states were identified. The s-wave states have expected spacing and width distributions, while the $\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ states behave anomalously. The $\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, $\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ strength functions were determined.     

Anomalous shape of cyclotron resonance line in n-GaP in high magnetic fields

Cyclotron resonance in n-GaP has been observed at 119 μm in pulsed magnetic fields up to 410 kG. From the experiments with the magnetic field parallel to the 〈100〉, 〈110〉 and 〈111〉 axes, it is concluded that the transverse effective mass for electron is and that the anisotropy factor of the conduction band is K = 7.9^+3.2_?2.0. An anomalous shape of the absorption curve was found in the magnetic field directions parallel to the crystal axes 〈110〉 and 〈111〉.     

Surface cyclotron resonance in Si under uniaxial stress

The cyclotron resonance of inversion-layer electrons on (100)p-type Si is found to depend sensitively on an externally applied compressive stress. At low temperatures (T ? 10 K) we observe a considerable increase of the cyclotron mass m¹_c with stress S along the [001] direction. The effect is most strongly observed at low electron densities n_s. For $\text{S～1.5 × 10}{}^9\text{dyne}\text{cm}{}^2$ and n_s～2 × 10¹¹cm^-2 we obtain $\text{m}{}^1{}_{\mathrm{c}}\text{～0.4 m}{}_0$ instead of the expected 0.2m₀. Along with this change of $\text{m}{}^1{}_{\mathrm{c}}$ a strong narrowing of the resonance is noted. Raising the temperature gives an additional n_s- dependent increase of $\text{m}{}^1{}_{\mathrm{c}}$.     

The origin of 3.55 eV emission band of RbCl:Tl

Fluorescence spectra of KCl:Tl, RbCl:Tl and NH₄Cl:Tl under A band excitation at room temperature (300 K) and liquid nitrogen temperature (77 K) have been re-examined in order to ascertain the origin of the 3.55 eV emission band of RbCl:Tl. The emission band at RT is found to show two components and the weaker component becomes dominant at LNT. The observations are explained in terms of Patterson's model of two local environments for Tl⁺ ion. One of them is a Tl⁺ having local CsCl like environment. The 3.55 eV emission band at 300 K is assigned to electronic transition in the Tl⁺ having local CsCl like environment.     

Electronic conductivity of AgI using D.C. polarization and charge transfer techniques

A Study of electronic conductivity using the d.c. polarization technique has been carried out in α and β-AgI which shows the former is a hole and the latter an electron conductor. Activation energies of undoped and Cu-doped single crystals and polycrystalline β-AgI were found to be 0.46 eV, 0.34 eV and 0.44 eV respectively and can be related to electron trap depths. The electron transference number ($\text{σ}{}_{\mathrm{\theta }}\text{σ}{}_{\mathrm{t}}$) for polycrystalline β-AgI was found to be 0.008 at 306 K. The activation energy for hole conduction in α-AgI was determined to be 0.97 eV in agreement with previous XPS studies.Transient measurements have also been conducted using the charge transfer technique in double cells of polycrystalline β-AgI. The carrier concentration C_θ and electron mobility μ_θ, have thus been estimated to be 1.8 × $\text{10}{}^{15}\text{cm}{}^3$ and 5.14 × 10^?5$\text{cm}{}^2\text{V}$?sec. respectively at 306 K, while the double layer capacitance was 0.496 $\text{μF}\text{cm}{}^2$.