Inhomogeneous Hole Research Articles

Interaction of coupled plasmon-phonon modes with a point charge in a polar semiconductor

The coupled plasmon--longitudinal-optical-phonon modes of a degenerate inhomogeneous electron or hole gas in a bulk compound semiconductor are studied. The interaction of a point charge with these coupled modes is derived in the random-phase approximation for both the carriers and the phonons in a form which is appropriate for treating inhomogeneous carrier systems. An integral equation governing the interaction of a static point charge with these coupled modes is derived which has the same form as that in the case of a point-charge interacting with plasmons alone but in which the parameters are modified by the coupling to phonons. As a specific example, these results are used to study the binding of the coupled plasmon-phonon modes to point charges in degenerate compound semiconductors, and it is found that such bound states will exist only at very low carrier densities.

Anomalous damping in MQW lasers due to slow inter-well transport

The authors present a model for MQW (multiple quantum well) lasers, using the laser rate equations, which includes transport of carriers between the individual wells of MQW lasers. This model provides the first consistent explanation for the anomalously high damping in MQW lasers. It is found that, while electron and hole transfer times both are of the order of 3 ps for typical InGaAs/InGaAlAs structures, hole transfer is much slower than electron transfer in InGaAs/InGaAsP structures, with the hole transfer time being of the order of 100 ps. Since the stimulated recombination times are of the order of 100 ps, this means that one may expect an inhomogeneous hole distribution for the latter case, whereas the carrier distribution is homogeneous for the former case. The effective differential gain derived from the resonance frequency vs. power is found to be almost equal for the two types of lasers. There is a significantly higher damping for the InGaAs/InGaAsP laser, which can be described by an effective gain compression factor almost four times higher than for InGaAs/InGaAlAs.

Magnetoresistance of thin inhomogeneous gold films

Thin gold films of various thickness (6 ⩽ t ⩽ 10 nm) are prepared in an uhv system at room temperature. As revealed by transmission electron microscopy (TEM) the films show inhomogeneous hole and channel structures of different sizes depending on the thickness of the films. The magnetoresistance of the films exhibits positive contributions at various (low) temperatures. For magnetic fields B < 0.5 T the experimental data can be well fitted by the theory as resulting from weak localization in 2D. In addition, this also makes it possible to separate contributions resulting from electron-electron interactions (EEI). We conclude—with respect to the TEM investigations—that in contrast to the resistance behavior resulting from WL, EEIs are very sensitive to the local structure of the thin gold films.

Determination of electrons scattering lengths in thin discontinuous gold-films

Thin gold-films of various thicknesses (6 nm< t<10 nm) are prepared in an uhv system at room temperature. As revealed by transmission electron microscopy (TEM) the films show inhomogeneous hole- and channel-structures of different sizes depending on the thickness of the films. Measurements of the temperature dependence of the resistance and the magnetoresistance at low temperatures yield distinct sets of scattering lengths (inelastic, spin-orbit, elastic) and the screening parameter F when fitting the experimental data by means of weak localization and electron-electron interaction theory in 2d. The topology of the films is taken into account.

Inhomogeneous Photochemistry and Hole Burning in Dihydrophenazine Doped Molecular Crystals

Abstract A series of photochemical products of 5,10 dihydrophenazine (PH2) doped in fluorene (Fl) crystals can be observed via optical and ESR spectroscopy upon two photon excitation of PH2. ESR spectra reveal the formation of host-guest triplet radical pairs as a product of a double hydrogen abstraction. The non-planar PH2 ground state leads to a strong site distribution. Photochemical hole burning experiments indicate that this distribution determines to some extent the reaction rate.

Conductivity and thermoelectric power of trigonal SexTe1−x single crystals

AbstractConductivity σ and thermoelectric power α of SeTe mixed crystals have been measured in the temperature range from 100 K up to the melting points. The activation energy of the intrinsic conductivity shows a relatively complicated dependence on alloy composition, which can be explained by a transition from the direct gap of Te to the indirect gap of Se at about 40% Se content. The extrinsic conductivity has an activation character in a large part of the system. Formally the activation energy ΔE has to be attributed to the mobility. It decreases continuously towards Te and vanishes at the high Te end. ΔE can be explained by a strongly inhomogeneous hole concentration as for trigonal Se. The density of states mass of holes has been estimated, which increases approximately linearly with Se content from 0.2 m0 for Te to about 1.4m0 for Se.

Magnetoconductivity of Trigonal Selenium Single Crystals

AbstractSix of the eight magnetoconductivity components of trigonal Se are measured up to 30 kG over the temperature range 83 to 300 °K. Unlike the Hall mobility, which increases exponentially with temperature, the magnetoconductivity mobility decreases with rising temperature and, at high temperatures, is approximately proportional to T−3/2. At 300 °K a value of 28 cm2/Vs is obtained for the mobility in the chain direction, whilst the Hall mobility at the same temperature is only about 0,2 cm2/Vs[1]. This discrepancy can be explained by assuming a strongly inhomogeneous hole concentration. The directional dependence of the magnetoconductivity is interpreted using a six‐ellipsoidal model. From this the ratio of the mobilities parallel and perpendicular to the chain direction is about 3.5.