Shift Of Energy Gap Research Articles

Energy Gap and Chemical Shift of X‐Ray K Absorption Discontinuity of Arsenic in Its Compounds

Energy Gap and Chemical Shift of X‐Ray K Absorption Discontinuity of Arsenic in Its Compounds

Phosphorus ion implantation induced intermixing of InGaAs-InP quantum well structures

We have studied P ion implantation induced intermixing of In0.53Ga0.47As quantum wells embedded between InP barriers. Data are presented for both standard furnace anneals at 650 °C and rapid thermal anneals at 750 °C. Low-temperature photoluminescence and quantitative Auger electron spectroscopy were performed for furnace-annealed samples for which photoluminescence shifts of ∼200 meV were in excellent agreement with the calculated band gap for the lattice matched composition determined by Auger spectroscopy. Photoluminescence studies of rapid thermal annealed samples yield an energy gap shift of ∼150 meV for annealing times of at least 10 s.

Temperature effects on the band-gap energy in p-type III-V semiconductors.

We apply a new expression for the valence-band random-phase-approximation dielectric function of semiconductors with a zinc-blende structure to determine the temperature dependence of the band-gap energy in p-doped GaAs. Our results demonstrate that the electronic contribution to the energy-gap shift is nearly temperature independent.

Molecular dynamics simulation of conformational transitions and solvatochromism of polydiacetylenes

Solvato- and thermochromism of polydiacetylenes (PDA) are explained in terms of concepts from molecular mechanics. The instability of the polymer chain structure with respect to small variations of the interaction parameters is a cause of the conformational transition accompanied by a colour change. The dynamics and kinetics of this transition have been investigated numerically by the molecular dynamics method. Special solutions of soliton type have been obtained in the continuous limit. Soliton collision has been simulated numerically and the lifetime of solitons has been determined. Changes of colour during the conformational transition are connected to the variation of electron-electron interaction parameters and to the corresponding energy gap shifts in the optical excitation spectrum.

Temperature shift of the absorption edge in mixed single crystals of ZnxCd1-xSe.

The thermal dependence of the absorption-edge shift has been measured in mixed single crystals of ${\mathrm{Zn}}_{\mathrm{x}}$${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$Se, in the temperature range 13--300 K. The experimental results support the argument that the energy gap shift is caused by an internal Franz-Keldysh effect which results from electric fields induced by phonons. However, the exact dependences of the energy gap shift and the increase in the absorption coefficient on the electric fields differ from those calculated by Franz and Keldysh, because of final-state interaction correction. It is shown that in mixed single crystals of ${\mathrm{Zn}}_{\mathrm{x}}$${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$Se, as well as in other single crystals of pure II-VI compounds, the electric fields which determine the thermal shift of the absorption edge are dominated by the LO-phonon-induced electric fields.

Superconductive Tunneling Parameters of Strain-Free Pb Films

Lead film tunnel junctions have been fabricated on Pb crystal substrates to reduce the thermal strain that arises upon cooling to liquid helium temperatures. The energy gap has been measured, 1.360 ± 0.007 meV, and compared to that obtained from similar films deposited on glass slide substrates, 1.390 ± 0.005 meV. The expected energy gap shift, due to the thermal strain, has been estimated and compared to the experimental result. The effect of this shift on previous measurements of energy gap anisotropy in Pb crystals is discussed. Changes in the phonon structure appearing in d2I/dV2 have also been measured.

Pressure dependence of transport and optical properties of Ag 2HgI 4

Silver mercury iodide, Ag 2HgI 4, has been studied to pressures of 75–100 kbar at 25°C. There are now four high pressure phases known. Transport studies indicate predominantly electronic conduction, with the highest pressure phase showing rectification in an asymmetric conductivity cell. Optical studies now corroborate the four high pressure phases. For two of the phases the energy gap shifts to lower energies with increasing pressure.

Optical Properties of Antiferromagnetic Chromium and Dilute Cr-Mn and Cr-Re Alloys

The antiferromagnetic energy gap and optical properties of single crystals of Cr and of Cr alloyed with 0.45, 0.94, 2.5, and 4.5% Mn and with 1.05 and 2.0% Re have been investigated by measuring the optical absorption over a photon energy range of 0.08-5 eV. The data were taken at 4.2 K by a calorimetric technique. It is found that at 4.2 K, approximately 1% Mn or Re will cause commensurate antiferromagnetic ordering, and the energy gap shifts abruptly from 0.13 to 0.36 eV near this concentration of diluent. Evidence is given for indirect transitions occurring across a double energy gap in the noncommensurate samples, and the results are explained in terms of a band model. The widths of the absorption peak and the peak in ${\ensuremath{\epsilon}}_{2}$ in the commensurate samples are discussed in terms of a gap anisotropy and impurity broadening. Optical absorption peaks near 1, 2, and 3.4 eV are associated with direct interband transitions originating from the $N_{1}^{\ensuremath{'}}$, $\ensuremath{\Gamma}_{25}^{\ensuremath{'}}$, and ${P}_{4}$ symmetry points, with a contribution to the 1-eV absorption from transitions from the Fermi surface to the flat unoccupied band extending through ${N}_{4}$, ${\ensuremath{\Gamma}}_{12}$, ${P}_{3}$, and $H_{25}^{\ensuremath{'}}$.

Abstracts of Bell System Technical Papers Not Published in This Journal

The method of effective mass, extended to apply to gradual shifts in energy band s resulting from deformations of th e crystal lattice, is used to estimate the interact ion between electrons of thermal energy and the acoustical modes of vibration. The mobili ties of electrons and holes are thus relat ed to the shifts of the conduct ion and va lence-bond (filled) hands, respectively, associated with dilations of longitudinal waves. The theory is checked by comparison of the sum of the shifts of the conduction and valence-bond bands, as derived from the mobilities, with the shift of the energy gap with dilation. The latter is obtained independently for silicon, germanium and tellurium from one or more of the followin g: (1) the change in intrinsic conductivity with pressure, (2) the change in resistance of an n-p junction with pressure, and (3) the variation of intrinsic concentration with temperature and the thermal expansion coefficient. Higher mobilities of elec trons and holes in germanium as compared with silicon are correlated with a smaller shift of energy gap with dilation.

Deformation Potentials and Mobilities in Non-Polar Crystals

The method of effective mass, extended to apply to gradual shifts in energy bands resulting from deformations of the crystal lattice, is used to estimate the interaction between electrons of thermal energy and the acoustical modes of vibration. The mobilities of electrons and holes are thus related to the shifts of the conduction and valence-bond (filled) bands, respectively, associated with dilations of longitudinal waves. The theory is checked by comparison of the sum of the shifts of the conduction and valence-bond bands, as derived from the mobilities, with the shift of the energy gap with dilation. The latter is obtained independently for silicon, germanium and tellurium from one or more of the following: (1) the change in intrinsic conductivity with pressure, (2) the change in resistance of an $n\ensuremath{-}p$ junction with pressure, and (3) the variation of intrinsic concentration with temperature and the thermal expansion coefficient. Higher mobilities of electrons and holes in germanium as compared with silicon are correlated with a smaller shift of energy gap with dilation.