Excitons In Germanium Research Articles

Far-Infrared Magneto-Spectroscopy of Shallow Impurities and Excitons in Germanium by Using Lasers

Far-Infrared Magneto-Spectroscopy of Shallow Impurities and Excitons in Germanium by Using Lasers

Dynamical Stark effect of bound excitons in germanium doped with beryllium or zinc

We report the inhomogenous line broadening of far-infrared magneto-absorption of excitons bound to the neutral double acceptor Be or Zn. We propose that the linewidth of a 1S-2P_ like transition of an electron in a bound exciton is dominated by dynamical Stark effect due to photo-generated free carriers. The linewidth † increases with electron density n as †∝n 0.3.

Far-infrared study of the Zeeman effect of indirect excitons in germanium

A series of experiments was performed to study the Zeeman effect of the lower quantum levels of indirect excitons in Ge with the use of infrared absorption in the presence of small magnetic fields which varied from 0 to 7 kOe in steps of 0.5 kOe. The magnetic fields were applied parallel to the $〈100〉$ crystallographic direction, in the Faraday geometry. An analysis of the observed behavior of the transitions was done using a simplified magnetic Hamiltonian. In this Hamiltonian we include the interaction of the field with the "intrinsic spin" of the hole $\stackrel{\ensuremath{\rightarrow}}{\mathrm{J}}=\frac{3}{2}$, with the spin of the electron and with the orbital angular momentum of the exciton envelope wave function. The only fitting parameters used were $g$ factors for the electrons and holes. With the use of a simplified set of exciton wave functions based on a set previously published by Lipari and Altarelli, a good fit is obtained to the observed behavior of most of the lines, with ${g}_{e}=1.5\ifmmode\pm\else\textpm\fi{}0.3$ and ${g}_{h}=3.8\ifmmode\pm\else\textpm\fi{}0.2$.

Evidence for an excited hole state of donor bound excitons in germanium and a parity selection rule

Measurements on luminescence associated with the decay of excitons bound to group V donors in germanium, previously carried out only in the no-phonon region, have been extended to the TA and LA phonon assisted regions. Bound exciton absorption and luminescence have also been investigated in lithium-doped germanium. These data provide strong evidence for an excited hole state for donor bound excitons and parity-sensitive selection rules.

Strain-narrowing of excitons in germanium

Strain-narrowing of excitons in germanium

Strain-narrowing of excitons in germanium

We have observed a narrowing of the luminescence line from excitons in germanium with the application of a uniaxial stress along the [111] crystallographic axis. In zero stress the line is broadened by the two split excitons and the mass-reversal effect, while at our stress of 15 kg mm 2 only one band is occupied. We find that the high stress density of states varies nearly as the square root of energy.

Far-infrared magneto-absorption of donor-bound excitons in germanium: Pseudo-acceptor model

The magneto-oscillatory absorption spectrum of the arsenic-bound excitons in germanium observed at 118.6 μm reveals a series of absorption lines similar to the Zeeman spectrum of the acceptor impurity. This fact indicates that the bound excitons have the excited states associated with the light-hole Landau ladders and these excited states can be described by the model of a hole bound to the D - state, i.e. the pseudo-acceptor model. The hole binding energy of the ground state of the bound excitons has been obtained to be 4.7 meV, which is smaller compared with the binding energy of the acceptor impurity.

Interpretation of far-infrared absorption spectra in germanium

The high resolution far-infrared absorption spectra of free excitons in germanium are analyzed for the first time using a model which accurately includes both the anisotropy of the valence and condition bands and the degeneracy of the valence band. The observed structure is in good agreement with the calculated transitions between the anisotropy split ground state and the various p-like excited states.

Further comments on the luminescence line shape of the free exciton in germanium

The free-exciton luminescence line shape in germanium has been measured as a function of crystal temperature and free-exciton density. In order to fit these data, the theory includes nonparabolicity effects, collision broadening, and Gaussian broadening. From this fit, the bottom of the free-exciton band is at 712.8 \ifmmode\pm\else\textpm\fi{} 0.1 meV and the electron-hole droplet binding energy is 1.9 \ifmmode\pm\else\textpm\fi{} 0.2 meV.

Far-Infrared Magneto-Spectroscopy of Shallow Impurities and Excitons in Germanium by Using Lasers

Optical transitions between excited states of impurities in germanium, Sb or As, in a magnetic field have been investigated using HCN, DCN and H20 lasers. The energy levels of states with even parity and M= +1, i.e., 3D+l, (113) and (115), are determined experimentally and are compared with the values obtained by the variational calculation. In pure germanium under photo-excitation, the Zeeman effect of the far-infrared absorption of an indirect exciton has been. observed. An attempt is presented to interpret the origin of the strong absorption peaks of the exciton on the basis of the adiabatic approximation for the Coulomb potential. The present work is concerned with optical transitions between the excited states of group V impurities in germanium and with transitions of an exciton from its ground state to an excited state in undoped germanium. Both the impurity and exciton in germanium have a series of hydrogen-like states; the optical transitions occur in the far-infrared region. The s- and d-like excited states can be observed only by the transitions starting from some excited states. On excitons, we have little information on their excited states, though the photo-luminescence experiments reveal the nature of the ground state. Since the densities of excited impurities and of excitons are rather small, certain intense light sources are required for the spectroscopic observation of these weak absorption. Such light sources are provided by backward tubes and far-infrared lasers.

Submillimeter Absorption Spectra and Phase Transition of Indirect Excitons in Germanium

The results are presented of the detailed studies on the exciton absorption spectra in ultrapure Ge in the spectrum regions 0.67-1.1 and 1.7-3.7 meV with a backward-wave tube radiation. It is shown that the measured spectrum corresponds to the exciton's transitions from the ground to excited states. As a result of temperature measurements at 1.6-4.2 K the phase transition of excitons into the condensed state has been observed without the formation of excitonic molecules.

Diffusion of Electron—Hole Drops and Excitons in Germanium

AbstractThe diffusion of electron—hole drops and of excitons has been investigated in pure and doped germanium. It was found that the diffusion lengths depend on doping level, temperature, and excitation intensity. Qualitative explanations of the results based on simultaneous motion of excitons and electron—hole drops are presented.

Condensation of excitons in germanium and silicon

The ground state energy of an electron-hole plasma in a Ge type semiconductor is calculated with the help of the 'improved RPA' approximation of Nozieres and Pines (1958). The detailed band structure is taken into account, except for the warping of the valence band. That is, the effects of the anisotropy, of the valence band coupling and of the multivalley structure are discussed, and are found to stabilize the plasma. The numerical results for Ge and Si are in very good agreement with experiments, which provides a check for the validity of the 'improved RPA' approximation.

Effective mass theoretical approach to optical and microwave phenomena in semiconductors—II: Theory of the Faraday and Voigt effects due to excitons in germanium

The oscillatory Faraday and Voigt spectra observed by Nishina and Lax near the direct band gap of germanium have been analysed on the effective mass theory of the excitons in a strong magnetic field. The effective mass equation is solved variationally and assignment of each rotational singularity is made. The exciton binding turns out to be essential for the interpretation of the rotation spectra at room temperature as well as at low temperature. The effect of the existing strain is emphasized in the low temperature spectrum. The sign reversal of the first Faraday singularity observed at low temperatures is accounted for as an interplay between the effects of strain and magnetic field on a degenerate band.

Fine Structure of the “One‐Dimensional” Exciton in Germanium in Parallel Magnetic and Electric Fields

AbstractThe excited states of a one‐dimensional exciton in finite magnetic fields represent doublets consisting of even and odd components. The differential electroabsorption technique was used to observe transitions to odd states of the one‐dimensional exciton in germanium in parallel magnetic and electric fields. An analysis of the differential electroabsorption spectrum in parallel magnetic and electric fields is given.

Effective mass theoretical approach to optical and microwave phenomena in semiconductors - II. Theory of the Faraday and Voigt effects due to excitons in germanium

In this chapter, functionalization of glasses by incorporation of different types of semiconductors was described. Predominantly the II–VI (e.g., ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe) and IV–VI (e.g., PbS, PbSe, PbTe) semiconductors incorporated silicate, borosilicate, phosphate, and fluorophosphate glasses were addressed. Their processing protocol was explained mainly with reference to the melt quenching technique followed by heat treatment. Sometimes sol-gel technique was also referenced. Optical absorption and photoluminescence properties were described in details. In addition to this, Raman spectroscopy and transmission electron microscopy were also discussed. Processing and properties of rare-earth doped II–VI semiconductor incorporated glasses were described elaborately including white light emission and application in light emitting diodes. Various functional applications of semiconductor incorporated glasses and exercises were provided at the end.

High field magnetoabsorption of the indirect transition exciton in germanium at 1⋯7°K

The indirect transition exciton magnetoabsorption has been studied in the Faraday geometry with the magnetic field perpendicular to the (100), (111), and (110) crystal faces respectively. The measurements were made at 1⋯7°K and at fields of up to 74 kG. At low fields (< 40 kG) the exciton energy levels change quadratically with magnetic field, in agreement with previous work carried out in the Voigt geometry. At high (> 40 kG) fields a linear behavior is observed. The experimental observations are discussed as well as the range of applicability of the present theory to them.

High field magnetoabsorption of the indirect transition exciton in germanium at 1.7°K

High field magnetoabsorption of the indirect transition exciton in germanium at 1.7°K

Electron-Hole Exchange Energy in Shallow Excitons

An effect of the electron-hole exchange correction in the effective mass equation for a shallow exciton is investigated. In the case of direct excitons in germanium and gallium arsenide it is shown that the exchange correction to the theoretical binding energy is large and may reconcile the discrepancy between the observed value and the simple effectivemass estimate of the binding energy. In the case of indirect excitons the exchange correction is small.

Exciton energy levels in germanium and silicon

The energies of the lowest-lying levels of the direct exciton in germanium and the indirect excitons in germanium and silicon have been calculated in the effective-mass approximation by a variational procedure. These energies are compared with the experimental values obtained from optical absorption experiments.