Electrical conduction mechanism and carrier trapping in β-metal free phthalocyanine single crystals

The dark electrical conductivity of β-metal free phthalocyanine single crystals has been investigated over the temperature range 273–600°K, at a reduced pressure of 10^?7 torr. The results obtained are in accordance with the model proposed by Barbe and Westgate[5] for this material, in which the energy gap between the top of the valence band and the bottom of the conduction band is determined to be 2·00 eV. At temperatures below about 410°K, the conduction process is consistent with the presence of an electron trapping level located 0·32 eV below the conduction band edge, with a density of 7×10¹⁶ cm^?3, and a donor level of density 2×10⁷ cm^?3 at the same energy. Above about 410°K, there is evidence to suggest that the conduction process is intrinsic.     

Indirect electronic transitions in alkali halate crystals-I (sodium and potassium chlorate crystals)

The long wavelength tail of the fundamental absorption in NaClO₃ and KClO₃ crystals has been analysed based on the theory of band to band transitions of Bardeen et al.[8] developed in the case of semi-conducting crystals. Evidence of phonon involvement in the transitions giving an indirect band gap is observed. The energies of the phonons involved in the process are the same for both the crystals, and agree well with combinations of prinicple frequencies of ClO₃^? ion, their overtones and also lattice phonons. The indirect band gap in these crystals varies with temperature more or less linearly and the rate of variation is ?3·8 × 10^?4 eV/K and ?5·0 × 10^?4 eV/K for sodium chlorate and potassium chlorate respectively.     

Pressure dependence of the absorption edge for Cd1-xMnxTe

The effect of pressure on the optical absorption edge of mixed crystals Cd_1-xMn_xTe with different manganese concentrations is reported. The observed absorption edge shifts to higher energy with increasing pressure at a rate of α=7?8×10^?3 eV/kbar and a second order coefficient of β=-4×10^?5 eV/kbar² for x<0.5, to lower energy with increasing pressure at a rate of α=-5.0 ×10^?3 eV/kbar for x?0.5. A phase transition occurs for all the samples studied. The absorption edge of the new phase is outside the wavenumber range of the instrument. The physical origins of different pressure coefficients are discussed in the light of the deformation potentials of energy band states and the hybridization of the Mn²⁺ 3d levels with the p-like states in the valence band.     

Optical absorption edge in SnS

Optical absorption in single crystals of tin sulfide has been studied at many temperatures between 100 and 300 °K, in the wavelength range 2·2–0·8 μ. From the interference fringe patterns the absorption coefficient, reflection coefficient and index of refraction as a function of wavelength were determined for two light polarizations (ε∥a and ε∥b). From an analysis of the data, indirect band gaps of 1·142 and 1·095 eV were found for the two directions of polarization. Also it was found that the phonon assisted transitions required the participation of two phonons at different energy thresholds with energies 0·033 or 0·038 eV and 0·082 or 0·113 eV, with reference to the two axis. The temperature dependence of the indirect band gap for each direction of light polarization is linear with a slope ?4·05 × 10^?3eV and ?4·37 × 10^?3 eV respectively.     

Photoelectronic investigations of semi-insulating p-type GaAs:Cr containing neutral chromium acceptors

A photoelectronic analysis of p-type GaAs:Cr, i.e. measurements of thermally stimulated currents and the dependences of photoconductivity and photo-Hall effect on photon energy, temperature and light intensity, have enabled trap locations and densities as well as properties of neutral chromium acceptors to be determined. Hole traps proved to be located at 0.15 and 0.23 eV above the valence band, and their densities have been estimated to be 10¹⁵ cm^?3 and 5 × 10¹⁶ cm^?3 respectively. Their occurrence is related to the presence of copper in the samples investigated. Neutral chromium acceptors are located at 0.77 eV above the valence band and are at a constant distance from the conduction band. Their photoionization cross-section is 3 × 10^?17 cm² while the photoexcited electron escape cross-section is about 10^?20 cm². The potential of a neutral Cr acceptor is of the delta function type with weak coulombic tails. The maximum radius of the Bohr orbit of an electron in the ground state is 4 atomic units.     

Iodine as a donor in CdS

Iodine doped single crystals of CdS were grown from the vapor phase. High temperature Hall effect measurements for the crystals equilibrated with Cd and S₂ vapors at temperatures between 700 and 1000°C gave the free electron concentration as a function of p_Cd or p_S2 and temperature. The results can be explained on the basis of a model in which the CdS is saturated with iodine at low p_Cd (=high p_S2) but unsaturated at high p_Cd.The solubility of iodine in CdS is given by c_t=1·73×10²²p_S2^?1/8 exp (?1·045 eV/kT) cm^?3 atm^?1/8=4·62×10¹⁹p_Cd^1/4 exp (?0·195 eV/kT) cm^?3 atm^1/4The formation of pairs (I_SV_Cd)′ from I_S^· and V_Cd″ is governed by the equilibrium constant K_{P(I, V)}=4 exp (≤1·1 eV/kT)If Cd diffusion occurs primarily by free vacancies, the Cd^* tracer self diffusion leads to a vacancy mobility of (1·2±0·5)×10^?5 cm² sec^?1 at 900°C, in agreement with results reported by Woodbury [12], but (7±3) times larger than reported by Kumar and Kroger [10].     

Trapping levels in PbI2

A first investigation on trapping levels in PbI₂, performed by the Thermally Stimulated Current (TSC) technique, is presented. Three hole trapping centers are evidenced at 0.12, 0.29 and 0.59 eV above the valence band, with densities ranging between 8 × 10¹⁴ and 5 × 10¹⁶ cm^?3 and capture cross-sections between 8 × 10^?21 and 3 × 10^?17 cm². The center at 0.59 eV is likely responsible for the relatively short trapping time in PbI₂, as determined with nuclear techniques. By using a particular method, the behaviour of hole drift mobility along the layers as a function of temperature is determined for the first time. Finally, the presence of a spurious peak, not sensitive to irradiation, is reported and discussed.     

Shubnikov-de haas effect in n-CdSnAs2

Shubnikov-de Haas oscillations in the transverse magnetoresistance of single-crystalline n-type CdSnAs₂ have been recorded at temperatures between 2 and 25 K in magnetic fields up to 5T. The electron concentration of the samples ranged from 2 × 10¹⁷ to 2 × 10¹⁸ cm^?3. The angular dependences of the oscillation periods and cyclotron effective masses showed that the conduction band exhibits an energy dependent anisotropy, obeying the Kildal band structure model. For the low-temperature values of the band parameters we found: a band gap E_g = 0.30 eV, a spin-orbit splitting Δ = 0.50 eV, a crystal field splitting parameter δ = ?0.09 eV, and an interband matrix element P = 8.5 × 10^?8eV cm. This simple four-level model was found to be not adequate to describe quantitatively the observed electronic effective g-factor for a sample with low electron concentration.     

锑化铟中载流子的复合过程

用定态光电导及光磁电的方法测量了p型n型InSb在85—290°K之间的电子及空穴的寿命。在室温附近,所有样品的截流子寿命都趋于同一值,在290°K时为3×10^-8秒。从寿命的绝对值及温度依赖关系,以及掺杂对寿命的影响,可以肯定在室温附近起主要作用的复合过程是带间碰撞复合过程。在200°K以下,p型样品中的电子寿命与空穴寿命有很大差别,表明有陷阱作用。用位于价带之上0.05eV的复合中心及位于导带之下0.11eV的电子陷阱能完满地解释200°K以下的寿命与温度的依赖关系。     

Desorption kinetics and directional dependence of the surface diffusion of potassium on stepped W(100) surfaces

Using a surface ionisation ion microscope the desorption parameters and the diffusion constant of potassium were measured on stepped W(100) surfaces. The activation energy of ionic desorption as well as the corresponding prefactor do not depend on the step density; the mean adsorption lifetime τ can be expressed as τ=1.6×10^?14s exp(2.44 eV/kT).Whereas the surface diffusion of potassium on “flat” W(100) and on W(S)-[9(100)×(110)] was found to be isotropic, on W(S)- [5(100)×(110)] and W(S)-[3(100)×(110)] it occurs preferentially parallel to the step direction. The diffusion constant D_∥ for this direction has roughly the same value for all investigated surfaces: D_∥=7.8×10^?2 cm²s^?1 exp(?0.42 eV/kT). For the direction perpendicular to the steps D⊥ depends on the step density, whereby the activation energy as well as the prefactor increase with increasing step density.     

Indirect electronic transitions in alkali halate crystals-II (sodium bromate and iodate) crystals

In the case of NaClO₃ and KClO₃ crystals, analysis of the long wavelength tail of their fundamental absorption revealed the active participation of the internal vibrations of the chlorate ion (Part I). In order to test the validity of the above interpretation the absorption spectra of two more halates with different anions namely sodium bromate and sodium iodate are analysed in a manner similar to that given in Part I. It is found that the principle internal vibrations of bromate and iodate ions are involved in the indirect transitions. The variation of indirect band gap with temperature is found to be ?2·5 × 10^?4 eV/K and ?2·9 × 10^?4 eV/K for sodium bromate and sodium iodate respectively.     

Fundamental reflection spectrum and the electronic band structure of chlorine-doped CdTe

The effect of chlorine impurity on the fundamental reflection spectrum and the electronic band structure of cadmium telluride crystals has been studied. At the impurity concentration N _Cl>5.0×10¹⁹ cm^?3, a peak appears in the reflectance spectra. This peak is due to electron transitions at the X point of the Brillouin zone from the upper split valence band to Cl levels lying 0.05 eV above the Γ minimum of the conduction band. The other features in the reflectance spectra and band structure are explained as being due to the effect of spin-orbit splitting at the X point and to indirect electronic transitions from the Cl levels to the Γ minimum.     

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.     

Measurement of Ar(I) and Ar(II) transition probabilities in LTE ARC plasmas

The transition probabilities of two Ar(I) lines and one Ar(II) line have been measured in emission on wall-stabilized argon arc plasmas (0·5×10⁵?p, Nm^-2?3×10⁵; 10,000?T, K?20,000; 10²²?N_e, m^-3?5×10²³) using the “method of best fit (MBF)”. The results (without line-wing correction) are for Ar(I) at 714·7 nm, A_nm=5·66×10⁵ s^-1±5%; for Ar(I) at 430·0 nm, A_nm=3·40×10⁵ s^-1±5%; for Ar(II) at 480·6 nm, A_nm=8·82×10⁷ s^-1±7%. These values were not influenced by deviations from LTE, which have been observed at electron number densities n_e?10²³ m^-3. The small uncertainties were achieved after careful corrections of different sources of error.     

Dipolar studies in CaF2 with Ce3+

Dielectric relaxation in CaF₂ doped with various amounts of Ce³⁺ (0·01 to 1·0 mol%) was measured. The value of the activation energy for orientation of the dipoles {Ce³⁺-F^? interstitial} was determined to be H = (0·46 ± 0·01) eV. The frequency factor was found to have the value τ_o = (5 ± 1) × 10^?15 sec, giving for the vibrational frequency of the interstitial the value ν_o = (5 ± 1) × 10¹³ sec^?1.The number of dipoles contributing to the dielectric loss peak was determined to be between 10¹⁷ and 8 × 10¹⁷ cm^?3 for the different doping amounts of Ce³⁺. Optical absorption measurements showed the existence of large aggregate bands. We could verify that there exists a second-order reaction of aggregation, which is responsible for the non-linearity found between optical absorption at 305 nm and the nominal concentration of Ce³⁺ in the samples. On the other hand, if we assume that the centers which contribute to optical absorption at 305 nm are those also responsible for the relaxation peak, we find that the number contributing to each process is not the same. We can define an interaction radius R as the minimum separation between two dipoles allowing them to contribute to the relaxation peak. From our experimental data R ? 3·8 × 10^?7 cm.     

On the 0.34 eV hole trap in irradiated boron-doped silicon

Abstract

A detailed deep level transient spectroscopy (DLTS) study has been carried out on a prominant hole trap at 0.34 eV above the valence band in irradiated p-type silicon. The boron concentration in the float zone and Czochralski-grown samples varied between 10¹² and 10¹⁶ cm^?3, and irradiations with 2.0 MeV electrons have been performed at nominal room temperature to total fluences of 1.0 × 10¹⁶ and 1.0 × 10¹⁷ e^?/cm². The introduction rate of the trap is strongly boron-dependent, while the oxygen content in the samples does not influence neither the trap production rate nor its observed annealing behaviour. In the light of these observations and other available data on this trap, a boron-carbon pair is here tentatively proposed as the defect identity. A previously unreported hole trap at 0.45 eV above the valence band has also been observed in this work in highly boron-doped material. The isothermal and isochronal annealing characteristics of both traps have been investigated up to 400°C.     

A study of the adsorption of oxygen on Ni(111) using auger electron spectroscopy: Chemical shifts and valence spectra

Auger electron spectra have been recorded when oxygen is adsorbed on a Ni(111) single crystal surface. For the coverage range θ < 1, an analysis of the plot of the peak to peak height (H) of the oxygen KVV (516 eV) transition versus the total number of molecules cm^2? impinging on the surface (molecular beam dosing) shows agreement with the kinetic mechanism proposed by Morgan and King [Surface Sci. 23 (1970) 259] for the adsorption of oxygen on polycrystalline nickel films. In this coverage range, no energy shifts of the nickel or oxygen Auger peaks were recorded.At coverages θ > 1 (standard dosing procedure) shifts in the valence spectra M_{2, 3}VV (61 eV) and L₃M_{2, 3}V (782 eV) of ?2.3 eV and ?1.8eV respectively are recorded at 1.4 × 10^?2 torr-sec. Up to these coverages no shift of the L₃VV transition (849 eV) is observed. A chemical shift of ?2.1 eV is recorded in the L₃M_{2, 3}M_{2, 3} Auger transition (716 eV) at 1.4 × 10^?2 torr-sec.In the coverage range θ > 1, shifts in the energy of the oxygen Auger peaks are observed. At 5.8 × 10^?3 torr-sec. the KVV (516 eV) and KL₁V (495.2 ± 0.3 eV) transitions show shifts of ?1.5 eV and ?(1.0 ±0.3) eV respectively. No shift up to this coverage is recorded in the KL₁L₁ (480.6 ± 0.3 eV) transition.     

Electron traps in GaS

Measurements performed on n-GaS by means of the space-charge limited current method indicate the presence of a deep trap for electrons, at 0.57 eV from the conduction band and with a density of about 2.3 × 10¹³cm^?3. Another deeper trap at 0.63 eV and with a density of 6 × 10¹²cm^?3 is probably also present. The results seem to confirm the validity of a new direct method of analysis. Traps are tentatively attributed to compensated sulphur vacancies.     

Temperature,injection level,and frequency dependences of the luminescence in lightly - and heavily-doped CdTe:In

The temperature dependence, injection level dependence, and modulation frequency response of cathodoluminescence have been measured in Te-rich CdTe:In for materials with In concentrations ranging from 3 × 10¹⁵cm^?3 to 1 × 10¹⁸cm^?3. In lightly-doped material, the 80 K luminescence shows sharp band-edge emission near 1.57 eV and a broad impurity-defect band near 1.4 eV. As temperature increases, the 1.4 eV band quenches out, leaving only the band-edge emission. In heavily-doped material, the band- edge emission is absent and the 80 K luminescence shows only the 1.4 eV band. As the temperature increases from 80 K to 300 K, the 1.4 eV band does not quench out but rather undergoes a complex evolution into a long tail on the band-edge emission which begins to appear at approximately 140 K. At a temperature of 200 K, where the luminescence of the heavily-doped material consists of a broad but structured band approximately 0.2 eV in width, frequency response measurements indicate that band-to-band transitions contribute to the high-energy part of the broad luminescence while the remainder of the band results from slower transitions. The frequency and temperature dependences suggest that the luminescence involves an impurity level that has merged with a band edge at an In concentration of $\text{1 × 10}{}^{18}\text{cm}{}^3$. We interpret this behavior as suggesting that the 1.4 eV luminescence in Te-rich CdTe:In results from a partially-forbidden transition between conduction band and a deep acceptor level rather than from an intracenter type of transition.     

The exciton absorption in deformed germanium

Absorption spectra at 77° K near the direct (κ = 0) exciton transition are reported for deformed and undeformed single-crystal films of n-type Ge oriented on (111); Elliott's theory is applied. The optical width of the forbidden band for this transition is found as E_{g 0} = (0.8821 ±±0.0002) eV, while the exciton binding energy is found as E_ex(0) = = (0.0016±0.0003) eV for undeformed Ge at 77 ° K. The mean temperature coefficient of E_g for κ = 0 in the range 77 °–297 ° K is (dE_g/ /dT)_p =?3.50 · 10^?4 eV/deg. The effects of thermoelastic deformation on the exciton spectrum give (dE_g/dT)_d = (?1.5±0.1) · 10^?4 eV/deg. The half-width σ ≈ 5 · 10^?4 eV of the exciton peak gives the exciton lifetime as gt ≥ 10^?12 sec.