Resonant Hole Research Articles

A permanent hole burning study of the FMO antenna complex of the green sulfur bacterium Prosthecochloris aestuarii.

A permanent hole burning study on the Fenna-Matthews-Olson, or FMO, antenna complex of the green sulfur bacterium Prosthecochloris aestuarii was carried out at 6 K. Excitation resulted not only in relatively sharp features resonant with the burn wavelength but also in broad absorbance changes in the wavelength region of 800-820 nm. The shape of the latter changes was almost independent of the wavelength of excitation. Evidence is given that they are induced by a different mechanism than that which causes the resonant holes and that they may be due to a conformational change of the protein. The original spectrum was restored upon warming to 60 K. The effective dephasing times T2, as obtained from the homogeneous line widths, increased from about 0.5 ps at 803 nm to >/=20 ps at 830 nm and are in good agreement with recent measurements of accumulated photon-echo and time-resolved absorbance changes.

STM-Induced Hydrogen Desorption via a Hole Resonance

We report STM-induced desorption of H from Si(100)-H(2$\times1$) at negative sample bias. The desorption rate exhibits a power-law dependence on current and a maximum desorption rate at -7 V. The desorption is explained by vibrational heating of H due to inelastic scattering of tunneling holes with the Si-H 5$\sigma$ hole resonance. The dependence of desorption rate on current and bias is analyzed using a novel approach for calculating inelastic scattering, which includes the effect of the electric field between tip and sample. We show that the maximum desorption rate at -7 V is due to a maximum fraction of inelastically scattered electrons at the onset of the field emission regime.

Strain-induced enhancement of resonant current of holes in multilayered heterostructures

We study the effects of axial strains and the admixture of resonant hole states on transmissivities and on partial and total currents of holes in multilayered structures. As an example, we have used strained ${\mathrm{Ga}}_{x}$In${}_{1\ensuremath{-}x}$As-InP double barriers under external fields and show different aspects of the surfaces of energy and the nature of the solutions for different forms of internal strain built in the interfaces. We discuss possible optimal strain conditions on coherent tunneling probabilities and total currents that may enhance transport properties of each type of carrier.

Stimulated far-infrared emission from combined cyclotron resonances in germanium

We have measured the spectrum of stimulated far-infrared emission from Be- and Zn-doped germanium single crystals in crossed electric and magnetic fields. The spectrum consists of broad radiation bands in the frequency range of $40--130{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ that are due to intervalence band transitions and new narrow emission bands with their center frequencies rising linearly with magnetic field. We demonstrate that the latter emission is due to cyclotron resonance hole transitions between Landau levels of the light-hole subband accompanied by simultaneous spin flip, ``combined resonances.''

Transport of carriers in a semiconductor polymer random chain: a renormalization approach

We present a theoretical study for the quantum transport of carriers in a random semiconductor polymer poly(p-phenylene vinylene) (PPV) chain with the benzoid rings partially replaced by quinoid rings. A renormalization approach maps the polymeric chain into an effective one-dimensional lattice and the transmission coefficient as a function of energy is computed by transfer matrix techniques. In the case of randomly-distributed quinoid rings the spectrum shows narrow peaks in the conduction and the valence bands which indicate the presence of special resonant electron and holes states, lying within a larger fraction of localized states. The obtained density of states (DOS) shows a bandgap smaller than the transmission gap between the electron and the hole resonance peaks, which implies that an electric voltage larger than the band gap is required to inject electrons and holes into the polymer. This could explain why the operating voltage of PPV light-emitting diodes (LEDs) is larger than the semiconductor gap, in sharp contrast to conventional semiconducting LEDs.

In situ RHEED control of direct MBE growth of Ge quantum dots on Si (0 0 1)

Abstract RHEED studies of the morphological transformation of germanium layers during their MBE growth on the Si(0 0 1) surface were carried out. Zero-streak profiles analysis were used to control the formation of coherent and dislocated germanium islands at the film thickness of more than 5 and 8 monolayers (ML), respectively. The dislocation-free islands formed at the first stage (4–8 ML) of the morphological transformation were employed for designing the structures with the self-organized Ge quantum dots. The effects of charge and size quantization of hole transport, such as the Coulomb blockade and the resonance hole tunneling through the discrete energy levels in the quantum dots were observed in these structures.

Tailored carrier escape rates in asymmetric double quantum wells

An experimental study of carrier escape in a series of p - i - n asymmetric double quantum well (ADQW) structures using time-resolved photoluminescence is presented. By performing complementary continuous-wave photoluminescence and photocurrent measurements the carrier escape times were extracted as a function of temperature and perpendicular applied electric field and compared with a quantitative model which includes the mechanisms of tunnelling, thermally assisted tunnelling and thermionic emission. Holes were found to dominate the escape rate, and in the light of this it is shown that if narrow wells are grown next to wider wells and nearer the p region a significantly enhanced carrier escape rate can result. This is explained by resonant hole tunnelling and may have implications in the design of QW modulator and solar cell devices with improved performance.

Observation of resonant hole tunnelling through a (110) oriented AlAs/GaAs/AlAs quantum well

Hole resonant tunnelling through the quantum well of an AlAs/GaAs/AlAs double-barrier diode grown on a (110) oriented substrate is reported. Fewer resonances are observed in the current - voltage characteristic of the device than in the characteristics of similar devices grown on (100) and (311)A oriented substrates. High magnetic fields have been used to examine the anisotropy of the energy-wavevector dispersion relations of the quantum well valence subbands of the (110) device. The dispersion of one of the resonances is found to be much greater than has been observed in (100) and (311)A oriented devices.

Valence-band mixing effects on exciton dipole terahertz emission from asymmetric triple quantum wells

We analyze the influence of band mixing on the dynamics of hole tunneling in asymmetric GaAs–Ga1−xAlxAs triple quantum wells. A combination of the time-dependent Schrödinger equation and the Luttinger Hamiltonian is used to calculate the terahertz radiation from excitons. When the electric field required for resonance of electrons between the central and right well coincides with the field needed for hole resonance between the central and left well the radiation is strongly increased. If this field coincides with the hole mixing field at k∥≠0, a new modulation of the dipole emission appears, being drastically affected in frequency and amplitude. The calculated effect is greater than previous results for asymmetric double quantum wells.

SOUND ABSORPTION QUALITIES OF A CYLINDER-SHAPED ISOLATED ACOUSTIC RESONATOR/CILINDRINĖS FORMOS VIENETINIO AKUSTINIO REZONATORIAUS GARSO ABSORBCINĖS SAVYBĖS

In the article, an isolated acoustic resonator consisting of a cylinder-shaped hole of variable volume and with large and variable diameter is theoretically analyzed. Theoretical formulaes by which sound absorption of such resonator is computed are presented. The computations incorporate the influence exerted by overtones, i.e. odd harmonics, and supplementary resonator mass upon sound absorption. A change in the sound absorbtion depending on the resonator hole diameter, the angle of sound wave incidence and its volume, i.e. the distance to the rigid surface, has been established. Sound absorption reaches its maximum at low frequencies and it depends strongly on the hole diameter. Under constant hole diameter, sound absorption does not depend on the resonator volume, i.e. the distance to the rigid surface. Absorption notably depends on the angle of sound wave incidence. When this angle increases, absorption also increases at resonant frequency, while the frequency itself moves towards higher frequencies. When the sound wave incidence is 90 degrees with respect to resonator, maximum absorption is already observed at high frequencies. Real and imaginary parts of the radiation impedance of cylindric hole and of the impedance of the hole itself, as well as their dependency on frequency are computed. In this case, hole impedance consists of the impedances of the hole and air resiliency. The influence exerted by the real and imaginary parts upon sound absorption has been established. The resonance takes place when the imaginary parts of radiation and hole impedances intersect.

Hole Resonance among More Than Two Carbazole Chromophores in Poly(N-vinylcarbazole)

Hole resonance among more than two chromophores for the radical cationic carbazole (CZ) group of poly(N-vinylcarbazole) (PVCZ) in solution was shown by the radical ion transfer method and charge resonance (CR) band measurements. The sample was PVCZ with its oligomers (degree of polymerization (DP) = 2-100). The hole transfer rate from the radical cationic CZ of the oligomers to a 2,5-dimethoxyaniline, which has a lower ionization potential than the CZ chromophore, decreased with an increase in the oligomer molecular weight due to the hole resonance among neighboring chromophores. Thus, the stabilization energy of N-vinylcarbazole oligomers increases with increase in DP. The peak position of the CR band can be a good measure of the degree of charge resonance. The peak wavelength of the CR band was red-shifted for the larger molecular weight oligomers. This shift also suggested the existence of charge resonance in PVCZ among more than two CZ chromophores.

SOUND ABSORPTION QUALITIES OF A CYLINDER-SHAPED ISOLATED ACOUSTIC RESONATOR

Summary In the article, an isolated acoustic resonator consisting of a cylinder-shaped hole of variable volume and with large and variable diameter is theoretically analyzed. Theoretical formulaes by which sound absorption of such resonator is computed are presented. The computations incorporate the influence exerted by overtones, i.e. odd harmonics, and supplementary resonator mass upon sound absorption. A change in the sound absorbtion depending on the resonator hole diameter, the angle of sound wave incidence and its volume, i.e. the distance to the rigid surface, has been established. Sound absorption reaches its maximum at low frequencies and it depends strongly on the hole diameter. Under constant hole diameter, sound absorption does not depend on the resonator volume, i.e. the distance to the rigid surface. Absorption notably depends on the angle of sound wave incidence. When this angle increases, absorption also increases at resonant frequency, while the frequency itself moves towards higher frequ...

FDMR in Low-Temperature Solids. 1. Theory

Various mechanisms of geminate recombination in spin-correlated radical ion pairs produced by radiolysis of organic solids under cryogenic conditions are considered and compared with experimental data. Single-step electron tunneling and slow resonant hole transfer are examined from the viewpoint of their manifestation in pulsed time-resolved fluorescence-detected magnetic resonance (FDMR). Two theoretical models treating the phenomenon are developed, and their predictions are compared with the experimental results. These models are found to be consistent with many observed features: t[sup [minus]1] decay kinetics, unusual evolution of the FDMR spectra with time, narrow radial distribution of the FDMR-active pairs, and efficient spin memory transfer from the primary pairs. However, with very few exceptions the tunneling theories fail to reproduce the exact scale of the effect and its dependence on solute concentration and thermalization distance of electrons. This discrepancy suggests that the negative charge is more mobile than predicted by the single-step tunneling model. 31 refs., 8 figs.

Spectral hole burning on silicon phthalocyanines isolated in an argon matrix

Irradiation of the monomeric phthalocyanine Hex 3SiO(SiPc)OSiHex 3 isolated in an Ar matrix at T=13 K with the 632.8 nm line of a He/Ne laser produces a resonant spectral hole in the vibrational sideband located about 700 cm −1 above the origin of the Q band. This hole is accompanied by several sideholes in the origin region. These permit a precise determination of several excited-state vibrational frequencies. For dimeric Hex 3SiO(SiPc-O-SiPc)OSiHex 3 in the same matrix the changes in the absorption spectra after irradiation into the Q band reveal an out-of-plane polarization of the bands which are not present in the monomer absorption. This points to substantial charge-resonance contributions to the excitonic coupling between the two SiPc units in dimeric Hex 3SiO(SiPc-O-SiPc)OSiHex 3.

On acoustic Helmholtz resonator and on its electromagnetic analog

A study of the acoustic Helmholtz resonator and of its electromagnetic analog (a cylinder with a narrow slit) is performed. For the associated Green functions, power series asymptotics with respect to a small parameter ε (‘‘radius’’ of the resonator hole or the width of the slit), and ln ε of poles τε with small imaginary parts are obtained by using the method of matching asymptotic expansions. The principal terms of solution asymptotics for corresponding boundary value problems are given.

Investigation of acoustic sensing for laser machining processes Part 1: Laser drilling

An acoustic sensing technique has been developed for the in-process sensing of the erosion front condition during laser machining. This paper presents an analysis of acoustic sensing for blind and through-hole drilling. Theoretical analysis of the relationship between resonant frequency and hole geometry were performed using a Helmholtz resonator and wave equation models. The theoretical estimates are compared to experimental results for the laser drilling of acrylic, aluminum oxide and steel. Process control schemes for hole depth and beam break-through regulation using acoustic sensing are proposed.

Quantum well luminescence due to minority photoelectrons in p-type resonant tunnelling structures

Photoluminescence spectroscopy is used to investigate p-type double-barrier resonant tunnelling structures based on GaAs/AlAs. Strong photoluminescence from the quantum well is observed due to recombination of resonantly tunnelling holes with minority photogenerated electrons, which also tunnel into the quantum well. The luminescence undergoes a red shift with increasing bias and its intensity shows peaks at biases corresponding to the first four hole resonances in the current-voltage characteristics. Two additional strong peaks are also seen in this intensity-bias plot, due to electron resonant tunnelling.

Dependence of resonant electron and hole tunnelling times between quantum wells on barrier thickness

We investigated resonant tunnelling of electrons and holes between coupled quantum wells using time-resolved luminescence spectroscopy. Exponential dependence of tunnelling times on barrier width is observed for electrons but not for holes. The tunnelling times of electrons are correctly described by a model which takes into account inhomogeneous broadening.

The conduction band spin splitting in type-I strained and unstrained (GaIn)As/InP quantum wells

We present the first successful optically detected magnetic resonance experiments (ODMR) on strained and unstrained Ga x In 1− x As/InP type-I quantum wells. The resonances attributed to electrons are in general anisotropic and detailed results are given for the composition range 0.4 < x < 0.6. Extrapolating to the binary end points, i.e. InAs and GaAs close agreement with existing results is found. The anisotropy is explained within a simple model using subband calculations. It also explains why single-sided p-type modulation doping reduces the electron-hole wavefunction overlap, increases the radiative life-times and allows for optical detection of magnetic resonance. A detailed discussion why hole resonances can be ruled out is given.

Cyclotron and intersubband resonance studies in [001] and piezoelectric [111] InAs/(Ga,In)Sb superlattices

Cyclotron resonance and inter-subband excitation experiments have been performed on superlattices of the semimetallic, strained type II system InAs/(Ga,In)Sb. We observe simultaneously one cyclotron resonance from the 2D electrons located in the InAs and two resonances from the 2D holes in the (Ga,In)Sb layers. The two hole resonances originate from the M J = ¦ 3 2 > states. We have found a strong crystallographic anisotropy in the hole masses between structures grown along [001] and [111]A orientations attributed to the strain decoupling of the heavy and light hole levels in the GrmGa 1- x In x Sb valence band. In addition, we demonstrate for the first time that intersubband resonances can be directly seen for the electrons at large tilt angles.