ENDOR investigations of Ge doped GaP

ENDOR measurements of germanium doped gallium phosphide show a SHF-interaction with one neighbour shell strong enough to resolve the splitting of lines caused by the mutual interaction of the different nuclei of the same shell. The symmetry and hyperfine parameters of four other neighbour shells have also been determined.     

Double acceptor bound exciton in Ge

Six photoluminescence lines from excitons bound to neutral zinc acceptors in germanium are observed. The six lines consist of three replicas associated with zero, TA and LA phonons. Two lines from each replica correspond to the transitions from the split ground states of the bound exciton complex. The binding energy of the bound exciton is found to be 3.2 meV.     

Optical properties of donor electrons in semimagnetic semiconductors

The cross section of the spin-flip Raman scattering and the absorption coefficient of the electric-dipole spin-resonance of donor electrons in Cd_1?x Mn_xSe are calculated. The exchange induced spin-splitting of a donor level is described taking into account three sources of a local magnetization: external magnetic field, thermodynamical fluctuations of magnetization and molecular field of the donor electron (bound magnetic polaron). The theory takes into account the selection rules appropriate for the hexagonal CdMnSe. The role played by fluctuations of composition is considered. It is suggested that a spin-flip line is inhomogeneously broadened by thermodynamical fluctuations of magnetization and additionally, in high fields, by fluctuations of the composition.     

Combined effects of donor and acceptor impurities on the thermoelectric properties of cadmium antimonide

A study was made of the effect of the simultaneous doping with donor (Te) and acceptor (Cu, Ag, Au) elements on the thermoelectric properties of CdSb. Doping with tellurium changes the p-type conductivity of the CdSb crystals to an n-type conductivity with an impurity (Te) activation energy of E_d = (0. 11 ± 0. 01) eV. Doping with an acceptor impurity changes the energy of the donor level, by E_d = 0. 14 eV for doping with silver, by E_d = 0. 10 eV for doping with gold and by E_d = 0. 095 eV for doping with copper. It is shown that the type of conductivity and the thermoelectric properties of CdSb can be adjusted in the desired direction through simultaneous doping with two impurities.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 90–94, June, 1970.     

Optical properties of GaP thin film measured by surface plasmon excitation

Surface plasmon excitation technique is applied to follow the optical properties of thin semiconductor film around the fundamental absorption. As an example, we present some preliminary results on GaP thin films evaporated onto silver layer.     

How energy transfer from a donor to an acceptor influences donor and acceptor fluorescence fluctuations

Fluctuations in the time instants of photon emission in donor and acceptor molecules with triplet levels are calculated by the Monte Carlo method. The statistical processing of these time instants makes its possible to obtain the distribution of photon number in both fluorescences. The presence of the triplet level makes it impossible to transfer the energy from donor to acceptor completely.     

Site-dependent donor and acceptor levels in 6 H-SiC

The photoluminescence of N- and Al- or Ga-doped 6 H-SiC has been studied. Radiative transitions between free electrons and holes bound to acceptors in cubic-like and hexagonal-like sites are assigned. Donor-acceptor pair transitions between donor and acceptor impurities in cubic-like and hexagonal-like sites are analyzed. From studies on these transitions, the ionization energies of impurities in cubic-like and hexagonal-like sites in 6 H-SiC are estimated to be 248.5 and 239 meV for Al acceptors, 333 and 317 meV for Ga acceptors, and 155 and 100 meV for N donors, respectively. The ratios of the ionization energies of acceptors in the cubic-like sites to the hexagonal-like sites are almost constant, ≈1.04-1.05. The origin of the difference of the ionization energies of impurities in the different sites is discussed on the basis of the quantum defect model. For acceptors this is mainly caused by differences in the local dielectric constants.     

Defining donor and acceptor strength in conjugated copolymers

ABSTRACT

The progress in efficiency of organic photovoltaic devices is largely driven by the development of new donor–acceptor (D–A) copolymers. The number of possible D–A combinations escalates rapidly with the ever-increasing number of donor and acceptor units, and the design process often involves a trial-and-error approach. We here present a computationally efficient methodology for the prediction of optical and electronic properties of D–A copolymers based on density functional theory calculations of donor- and acceptor-only homopolymers. Ten donors and eight acceptors are studied, as well as all of their 80 D–A copolymer combinations, showing absorption energies of 1.3–2.3 eV, and absorption strengths varying by up to a factor of 2.5. Focus lies on exhibited trends in frontier orbital energies, optical band gaps, and absorption intensities, as well as their relation to the molecular structure. Based on the results, we define the concept of donor and acceptor strength, and calculate this quantity for all investigated units. The light-harvesting capabilities of the 80 D–A copolymers were also assessed. This gives a valuable theoretical guideline to the design of D–A copolymers with the potential to reduce the synthesis efforts in the development of new polymers.     

Excited donor and acceptor states in zinc telluride

Excited shallow donor and acceptor states are observed in excitation spectra of donoracceptor pair luminescence in ZnTe. The experiments yield a donor ionization energyE _D =18.3±0.3 meV, and from the Li acceptor 2P _3/2, 2P _5/2( ₈), and 2P _5/2( ₇) states valence band parametersµ=0.60±0.10 and=0.22±0.05. The latter exceeds values derived from other experiments and indicates considerable nonspherical perturbations associated with this acceptor requiring an extension of existing theories for shallow acceptor states.     

Optical phonons of circular wires in porous GaP

The reflection spectra of porous gallium phosphide samples are investigated in the far infrared region of wave numbers (10–700 cm^?1). In addition of the longitudinal and transverse optical phonon modes corresponding to the bulk material, additional vibrational modes are detected. Their number and spectral position are correctly described by a model of a dispersive dielectric medium under the assumption that porous gallium phosphide is formed by crystallites whose shape is close to cylindrical. It is concluded that such vibrational modes are optical phonons confined by the volume of the quantum wire. The experimental optical reflection spectra are used to obtain estimates of the average diameter of nanocrystallites forming the porous GaP layer.     

Effect of distance between acceptor and donor on optical properties of composite semiconducting polymer films

The excitation energy transfer from poly(N-vinylcarbazole) (PVK) to tris(8-hydroxyquinoline) aluminum (Alq₃) in composite films was investigated by adding an inert polymer, poly(methyl methacrylate) (PMMA). The energy transfer efficiency calculated from the photoluminescence (PL) excitation spectra is consistent with that from the time-resolved PL decay data of the composite films. We have found a linear relationship between the two kinds of the distances, which are calculated according to volume density and the Förster theory. Experimental results and analyses provide a facile method to infer the energy transfer efficiency and the distance between the donor and the acceptor molecules in the composite films.     

The gold donor and acceptor level in p-type silicon

DLTS measurements on the gold donoe and acceptor level in p-type silicon and reported. From the experimental data it must be concluded that the gold donor and the acceptor level are caused by the same defect, that the acceptor level lying 0.546eV below the conduction band is temperature independently pinned to the conduction band and that the hole capture cross section of the acceptor level

_P^A is temperature independent in the measured range of 215 to 345 K.     

Optical and ESR analysis of the Fe acceptor in InP

Photoluminescence (PL), optical absorption, and electron spin resonance (ESR) have been applied to detect the different charge states of substitutional Fe in InP. The 3d⁶ one electron trap state is detected by the PL and optical absorption lines of the ⁵T₂?⁵E transitions, whereas the 3d⁵ neutral acceptor state is identified by its characteristics S = 5/2 ESR signal.     

Structural properties of Si and GaP

Total energies are calculated for crystalline Si and GaP within the local-density functional formalism using first principles non-local pseudopotentials. Ground state structural properties (total energy, bulk modulus and lattice constant) are obtained for Si and GaP and are in good agreement with experimental values (differences < 6%). Si is used as a test and compared with other theoretical calculations.     

Optical properties of a donor impurity in a two-dimensional quantum pseudodot

We investigate the linear and nonlinear optical properties of a donor impurity confined by a two-dimensional pseudoharmonic potential both including harmonic dot and antidot potentials in the presence of a strong magnetic field. Calculations are made by using the perturbation method and the compact density-matrix approach within the effective-mass approximation. Based on the computed energies and wave functions, the linear, third-order nonlinear and total optical absorption coefficients as well as the refractive index changes have been examined. The results are presented as a function of the incident photon energy for the different values of the chemical potential of the electron gas and the zero point of the pseudoharmonic potential. The results show that the optical properties of a donor impurity in a two-dimensional pseudoharmonic QD are strongly affected by the zero point of the pseudoharmonic potential, the chemical potential of the electron gas and the Coulomb interaction.     

Periodically changing morphology of the growth interface in Si, Ge, and GaP nanowires

Nanowire growth in the standard <111> direction is assumed to occur at a planar catalyst-nanowire interface, but recent reports contradict this picture. Here we show that a nonplanar growth interface is, in fact, a general phenomenon. Both III-V and group IV nanowires show a distinct region at the trijunction with a different orientation whose size oscillates during growth, synchronized with step flow. We develop an explicit model for this structure that agrees well with experiment and shows that the oscillations provide a direct visualization of catalyst supersaturation. We discuss the implications for wire growth and structure.