Determination of the susceptibility mass of heavy holes in Pb1−xSnxTe compounds by plasma reflection spectra

Plasma reflection spectra of the Pb_1?xSn_xTe alloy samples with x = 0.19 have been studied in the temperature range 82–400 K. It has been found out that the plasma minimum is shifted towards long waves with an increase of temperature from 82 to 300 K. This shift is caused by the increase of the hole mass because of hole redistribution into an additional band. A susceptibility mass of the additional band of heavy holes has been determined. Its value turned out equal to 0.144m₀.     

An approximate mean absorption coefficient for H2O

An approximate mean absorption coefficient was obtained for the rotation spectrum of H₂O from the Fourier transform of the molecular dipole autocorrelation function. The correlation function was calculated using classical mechanics to describe the rotation of the molecule. The expression for the absorption coefficient was parameterized to facilitate the determination of the temperature dependence of the absorption coefficient. A comparison was made between the classical and the quantum-mechanical calculations of the mean absorption coefficient for the pure rotation band of H₂O at 250, 300 and 500°K. The agreement between the classical and quantum-mechanical calculations may be improved if corrections for quantum effects are introduced into the classical calculations. A method is given for generalizing the results for the pure rotation band to the vibration-rotation bands. The mean absorption coefficient of water vapor was used to compute the thermal radiative flux in a heavy pure water vapor atmosphere. The results of these calculations were compared with those of an existing calculation in which the absorption due to water vapor was given by a gray approximation.     

Electronic Raman scattering from inter-valence band transition in photo-excited GaP and GaAs1−xPx crystals

Raman scattering from photo-created free carriers in undoped GaP and GaAs_1?xP_x (x = 0.85, 0.73 and 0.66) under high excitation intensity has been studied. Two new Raman bands have been observed and assigned to electronic transitions from the split-off hole band to the heavy hole band and from the light hole band to the heavy hole band. The spin-orbit splitting energies in these crystals have been determined from the analysis of observed Raman bands, and compared with other experimental values.     

Model for the blue photoluminescence of cadmium sulfide

A model for the blue luminescence of polycrystalline cadmium sulfide and cadmium sulfide single crystals is proposed on the basis of a joint study of the absorption, reflection, emission, and excitation spectra of this luminescence at 77 °K. The blue luminescence arises in the transition of an electron from the conduction band to the 5s^{2 1}S₀ ground level of a super-stoichiometric cadmium atom which has trapped a hole from the valence band. The width of the energy gap (2.614 eV) at κ = 0 is estimated on the basis of the oscillatory nature of the excitation spectrum for the blue luminescence, and the effective mass of heavy holes is estimated.     

Magneto-optics and strain effects in GaInAsAlInAs and GaInAsInP quantum wells

Transitions between the Landau levels of the lowest electron and hole sub-bands have been observed in the inter-band optical absorption of a modulation doped Ga_.47In_.53AsAl_0.48In_.52As superlattice and a Ga_0.3In_.7AsInP strained layer superlattice, in magnetic fields up to 16T. In the unstrained sample, the energies of transitions up to 250 meV above the GaInAs band gap were found to be well described by a parabolic model for the heavy hole band and the model of Bowers and Yafet for the conduction band. In contrast to previous work on undoped quantum wells, no Coulomb binding effects were observed in this lightly doped sample, and this is attributed to screening of the exciton. In the strained sample, the heavy hole sub-band was found to show highly non-parabolic structure, and this is believed to be due to the effects of biaxial strain on the valence band.     

Optical properties of aluminum dodecaboride (α-AlB12) in the region of the transparency window

The absorption coefficient of α-AlB₁₂ was measured on single crystal samples at T=300 K within a broad spectral region (0.6–25 μm). In the region of the transparency window (3–6 μm), the absorption coefficient was measured in the temperature range from 165 to 650 K. An analysis of the experimental data shows that the energy spectrum of local states in the α-AlB₁₂ bandgap has certain features. It was established that a broad band of local states lies near the conduction band and that a trap level is located at 0.11±0.02 eV from the top of the valence band. __________ Translated from Fizika Tverdogo Tela, Vol. 43, No. 9, 2001, pp. 1573–1574. Original Russian Text Copyright ? 2001 by Zaitsev, Fedorov, Golikova, Orlov. Deceased.     

Electronic structures of the zinc-blende GaN/Ga1−xAlxN compressively strained superlattices and quantum wells

The electronic structures of the zinc-blende GaN/Ga_0.85Al_0.15N compressively strained superlattices and quantum wells are investigated using a 6×6 Hamiltonian model (including the heavy hole, light hole and spin-orbit splitting band). The energy bands, wavefunctions and optical transition matrix elements are calculated. It is found that the light hole couples with the spin-orbit splitting state even at thek=0 point, resulting in the hybrid states. The heavy hole remains a pure heavy hole state atk=0. The optical transitions from the hybrid valence states to the conduction states are determined by the transitions of the light hole and spin-orbit splitting states to the conduction states. The transitions from the heavy hole, light hole and spin-orbit splitting states to the conduction states obey the selection rule Δn=0. The band structures obtained in this work will be valuable in designing GaN/GaAlN based optoelectronic devices.     

Transient optical absorption of hole polarons in ADP (NH4H2PO4) and KDP (KH2PO4) crystals

A study of transient optical absorption of the ADP (NH₄H₂PO₄) and KDP (KH₂PO₄) nonlinear crystals in the visible and UV spectral regions is reported. Measurements made by absorption optical spectroscopy with nanosecond-time resolution established that the transient optical absorption (TOA) of these crystals originates from optical transitions in the hole A and B radicals and the optical-density relaxation kinetics is rate-controlled by interdefect tunneling recombination, which involves these hole centers and the electronic H⁰ centers representing neutral hydrogen atoms. At 290 K, hole polarons and the H⁰ centers undergo thermally stimulated migration, which is not accompanied by carrier ejection into the conduction or valence band. The slow components of the TOA kinetics with characteristic times from a few tens of milliseconds to a few seconds can be assigned to diffusion-controlled annihilation of hydrogen vacancies associated with impurity or structural defects.     

Band structure enhancement of indirect transitions

Indirect and direct transitions in Ga_xIn_1?xP alloys has been studied in modulation spectroscopy, between 10 and 300 K. Deviation from simple indirect absorption has been studied and shown to be consistant with a model which takes into account band structure enhancement of the absorption coefficient at alloy composition values where direct and indirect edges occur, at nearly the same energy. For the first time we observe structures of Δε₁ corresponding to band structure enhanced indirect transitions.     

Kinetic properties of p-Mg2SixSn1 ? x solid solutions for x < 0.4

The results of a study of Mg₂Si _x Sn_{1 − x} solid solutions (x = 0.25, 0.3, 0.35, 0.4) are reported. The measurements performed cover the Seebeck coefficient, electrical conductivity and the Hall coefficient over broad ranges of temperatures (80–700 K) and carrier concentrations (10¹⁸ to 6 × 10²⁰ cm⁻³). These measurements were used to derive the band structure parameters (band gap, hole mobility, hole effective mass). The effective mass of holes was found to grow strongly with an increase in their concentration.     

Electronic transport in strained p-modulation Be-doped Ga0.8In0.2As/GaAs single quantum well

We report on the electronic transport properties of p-modulation Be-doped Ga_0.8In_0.2As/GaAs single quantum well. The experiments included the spectral photoluminescence between 8 and 300?K, and Hall effect measurements at temperatures between 14 and 300?K. The effect of strain which induces splitting of the valence band as light and heavy hole bands on transport is discussed. The calculated band alignment of the GaInAs sample using model-solid theory including strain effects indicates large conduction band discontinuities and a much smaller valance band discontinuity in GaInAs. The effect of the conduction and valance band discontinuity on the electronic transport properties is also discussed.     

Nonradiative relaxation of photoexcited O<Stack><Subscript>1</Subscript><Superscript>0</Superscript></Stack> centers in glassy SiO<Subscript>2</Subscript>

The processes involved in the excited-state relaxation of hole O ₁ ⁰ centers at nonbridging oxygen atoms in glassy SiO₂ were studied using luminescence, optical absorption, and photoelectron emission spectroscopy. An additional nonradiative relaxation channel, in addition to the intracenter quenching of the 1.9-eV luminescence band, was established to become operative at temperatures above 370 K. This effect manifests itself in experiments as a negative deviation of the temperature-dependent luminescence intensity from the well-known Mott law and is identified as thermally activated external quenching with an energy barrier of 0.46 eV. Nonradiative transitions initiate, within the external quenching temperature interval, the migration of excitation energy, followed by the creation of free electrons. In the final stages, this relaxation process becomes manifest in the form of spectral sensitization of electron photoemission, which is excited in the hole O ₁ ⁰ -center absorption band.     

Anomalous enhancement of the thermoelectric power in gallium-doped p-(Bi1 ? xSbx)2Te3 single crystals

The effect of gallium on the temperature dependences (5 K ≤ T ≤ 300 K) of Seebeck coefficient α, electrical conductivity σ, thermal conductivity k, and thermoelectric efficiency Z of mixed p-(Bi_0.5Sb_0.5)₂Te₃ semiconductor single crystals is studied. The hole concentration decreases upon gallium doping; that is, gallium causes a donor effect. The Seebeck coefficient increases anomalously, i.e., much higher than it should be at the detected decrease in the hole concentration. This leads to an enhancement of the thermoelectric power. The observed changes in the Seebeck coefficient indicate a noticeable gallium-induced change in the density of states in the valence band.     

Investigation of structural and optical properties of 100 MeV F7+ ion irradiated Ga10Se90-xAlx thin films

Present work focuses on the effect of swift heavy ion (SHI) irradiation of 100 MeV F⁷⁺ ions by varying the fluencies in the range of 1 × 10¹² to 1 × 10¹³ ions/cm² on the morphological, structural and optical properties of polycrystalline thin films of Ga₁₀Se_90-xAl_x (x = 0, 5). Thin films of ~300 nm thickness were deposited on cleaned Al₂O₃ substrates by thermal evaporation technique. X-ray diffraction pattern of investigated thin films shows the crystallite growth occurs in hexagonal phase structure for Ga₁₀Se₉₀ and tetragonal phase structure for Ga₁₀Se₈₅Al₅. The further structural analysis carried out by Raman spectroscopy and scanning electron microscopy verifies the defects or disorder of the investigated material increases after SHI irradiation. The optical parameters absorption coefficient (α), extinction coefficient (K), optical band gap (E_g) and Urbach’s energy (E_U) are determined from optical absorption spectra data measured from spectrophotometry in the wavelength range 200–1100 nm. It was found that the values of absorption coefficient and extinction coefficient increase while the value of optical band gap decreases with the increase in ion fluence. This post irradiation change in the optical parameters was interpreted in terms of bond distribution model.     

Transient optical absorption and luminescence of lithium triborate LiB<Subscript>3</Subscript>O<Subscript>5</Subscript>

The transient optical absorption and luminescence of LiB₃O₅ (LBO) nonlinear crystals in the visible and UV spectral ranges were studied. Measurements made using absorption optical spectroscopy with nsscale time resolution revealed that the transient optical absorption (TOA) in LBO originates from optical transitions in hole centers and that the kinetics of optical density relaxation are rate-limited by interdefect nonradiative tunneling recombination involving these hole centers and the Li⁰ electronic centers, which represent neutral lithium atoms. At 290 K, the Li⁰ centers can migrate in a thermally stimulated, one-dimensional manner, a process which is not accompanied by carrier delocalization into the conduction or valence band. It is shown that the pulsed LBO cathodoluminescence kinetics is rate-limited by a recombination process involving two competing valence-band-mediated hole centers and shallow B²⁺ electronic centers. The radiative recombination accounts for the characteristic σ-polarized LBO luminescence in the 4.0-eV region.     

Transient optical absorption and luminescence in Li2B4O7 lithium tetraborate

This paper reports on a study of the transient optical absorption exhibited by Li₂B₄O₇ (LTB) in the visible and UV spectral regions. Using absorption optical spectroscopy with nanosecond time resolution, it is established that the transient optical absorption (TOA) in these crystals originates from optical transitions in hole centers and that the kinetics of the optical-density relaxation is controlled by interdefect tunneling recombination, which involves these hole centers and electronic Li⁰ centers representing neutral lithium atoms. At 290 K, the Li⁰ centers migrate in a thermally stimulated, one-dimensional manner, without carrier ejection into the conduction or valence band. The kinetics of the pulsed LTB cathodoluminescence is shown to be controlled by a relaxation process connected with tunneling electron transfer from a deep center to a small hole polaron migrating nearby, a process followed by the formation of a self-trapped exciton (STE) in an excited state. Radiative annihilation of the STE accounts for the characteristic σ-polarized LTB luminescence at 3.6 eV, whose kinetics is rate-limited by the tunneling electron transfer.     

Infrared modulated reflectance spectra of n and p type gallium antimonide and n type indium antimonide

We have observed the modulated reflectance spectra of n and p type GaSb at 300, 80, and 5 K from 0.56 to 2 eV. The modulated reflectance of intrinsic n type InSb was measured at 80 K from 0.2 to 2 eV. The “dry sandwich” vapor deposition technique was used to make the electroreflectance (ER) samples. The low-temperature spectrum of the undoped p type GaSb sample shows three peaks at the band edge that could be associated with transitions from the top of the valence band, the light (0.903 eV) and heavy (1.014eV) hole state Fermi levels to the conduction band. The energies of the observed peaks are in agreement with the Fermi level determination from Hall effect and Faraday rotation measurements. This modulation mechanism is based on band population effects. The ER signal of InSb under flatband condition at 80 K has five half oscillations at the direct band gap. The contribution of piezoelectric strain to ER is present since the dc bias required to achieve flatband condition is different at the band gap than at E₁. The ER signal corresponding to the direct gap energy E₀ and to the spin-orbit energy E₀ + Δ₀ was determined in the n and p type samples of GaSb at different temperatures. We have measured the intrinsic energy gap in GaSb at room temperature. E_g = 0.74 eV. The corresponding spin-orbit splitting was found to be Δ₀ = 0.733 ± 0.002 eV.     

Steady state and time-resolved magneto-luminescence in ZnSe/(Zn,Mn)Se Heterostructures

We report on optical measurements performed on two 53Å and 106Å wide ZnSe quantum wells separated by a 350Å thick Zn_0.73Mn_0.27Se barrier. The measurements were performed by means of cw photoluminescence up to 20T, cw photoluminescence excitation and time-resolved photoluminescence spectroscopies up to 9T, at low temperature (4.2K). The fundamental optical transition changes its nature from a type-I light hole excition to a type-II heavy hole exciton as a function of applied magnetic field. Calculations taking into account the strain, Zeeman, and excitonic effects support the experimental findings and allows us to specify the value of the relative valence band offset.     

Semimetallic electrical transport in PbTe-SnTe superlattices on KCl substrate

The electrical resistivity and Hall coefficient (R_H) in PbTe-SnTe superlattices on KCl are measured between 4.2 and 300 K. Magnetic field dependence of R_H shows a sign inversion of R_H for a specimen of PbTe-SnTe with 100-50 A at 5 K. This is due to coexistence of electrons and holes. PbTe-SnTe superlattices are of type II, where the valence band edge of SnTe is higher than the conduction band edge of PbTe. From the magnetic field dependence of R_H, the electron and hole concentrations are calculated and the band-offset between PbTe and SnTe is estimated. The possibility of the structural phase transition of these superlattices is also discussed.     

Correlation between the anisotropy of hopconduction magnetoresistance and reciprocal band masses in Ge

Near 70 kG the d.c. magnetoresistance of phonon-assisted hopping of charge carriers between shallow impurities is found to have an anistropy depending on the reciprocal effective mass calculated from the L₁ conduction band minima in the case of n-type Ge and from the heavy hole component of the Γ′₂₅ valence band maximum in case of p-type Ge. These correlations are discussed and it is suggested that they are connected with the symmetry of the impurity wave functions and that the magnetic field tends to remove the light hole component of an acceptor wave function.