Temperature-modulated photoluminescence induced by photoexcitation in semiconductors

A new technique of temperature-modulated photoluminescence is reported. The periodic heating is induced by metastable optical radiation. An analysis is made of phase shifts. The technique is applied to GaP : N. The results are compared with those obtained with an external heater.     

Ultrafast relaxation processes in semiconductors

A brief review of theoretical studies concerning ultrafast relaxation processes in direct-gap polar semiconductors is presented. Comparison with measurement of time-resolved optical spectra in GaAs is shown.     

Terahertz impurity luminescence under the interband photoexcitation of semiconductors

The observation of intense terahertz luminescence under the interband photoexcitation of n-GaAs and p-Ge semiconductors at low temperatures is reported. The terahertz photoluminescence is caused by radiative transitions, which accompany the capture of nonequilibrium carriers by impurity centers. These centers are in turn created in the crystal due to the impurity-assisted electron-hole recombination. The external quantum yield of the luminescence reaches 0.1%.     

Ultrafast light-induced magnetization dynamics of ferromagnetic semiconductors

We develop a theory of ultrafast light-induced magnetization dynamics in ferromagnetic semiconductors. We demonstrate magnetization control during femtosecond time scales via the interplay between nonlinear circularly polarized optical excitation, hole-spin damping, polarization dephasing, and Mn-hole-spin interactions. Our results show magnetization relaxation and precession for the duration of the optical pulse governed by the nonlinear optical polarizations and populations.     

Ultrafast spin dynamics including spin-orbit interaction in semiconductors

This Letter presents a theoretical investigation of ultrafast spin-dependent carrier dynamics in semiconductors due to strong spin-orbit coupling using holes in bulk GaAs as a model system. By computing the microscopic carrier dynamics in the anisotropic hole-band structure including spin-orbit coupling, we obtain spin-relaxation times in quantitative agreement with measured hole-spin relaxation times [Phys. Rev. Lett. 89, 146601 (2002)10.1103/PhysRevLett.89.146601]. We show that different optical techniques for the measurement of hole-spin dynamics yield different results, in contrast to the case of electron-spin dynamics.     

Fano resonances in the impurity photoexcitation spectra of semiconductors doped with shallow donors

A theory describing the photoexcited current peaks in the spectral region corresponding to the energies of longitudinal optical phonons in semiconductors doped with shallow donors is developed. The experimental data available for n-GaAs are in good agreement with the results obtained using the proposed theory.     

Ultrafast vibronic phase transitions induced in semiconductors by femtosecond laser pulses

The intermode anharmonic interaction in the theory of ultrafast (t∼10⁻¹³ s) vibronic phase transitions induced on semiconductor surfaces (Si, GaAs) by femtosecond laser pulses is calculated. The conditions for plasma-induced transitions either to a state of chaotic disorder in the positions of the atoms (“cold liquid”) or into a state with crystal symmetry different from the initial symmetry (a new crystalline phase) are determined. It is shown that a NaCl-type structure is realized in GaAs for a transition of the second type, the transition being due to the instability of the longitudinal optical phonon branch. The corresponding numerical estimates are made for Si and GaAs. Fiz. Tverd. Tela (St. Petersburg) 41, 1462–1466 (August 1999)     

Transient and steady state lateral charge transport in polymeric semiconductors

The Lateral photovoltaic effect (LPE) has been used as an effective tool to probe the dynamics of photogenerated charge carriers in conjugated polymer based optoelectronic devices. In this paper, we analyze the time-dependence of LPE in a position sensing device geometry using a discrete circuit equivalent model coupled with a spreading impedance approach. We elucidate the dependence of the lateral photovoltage (LPV) on the position, intensity and the modulation frequency (ω _c ) of the light beam. Previous experimental results for the position and ω _c dependence of the LPV in the steady state are successfully reproduced within the present approach. We predict a clear knee-like feature in the transient regime of the LPV for high photocurrent values. This feature prompts us to propose that the response time of the organic position sensing device decreases sharply with increasing incident intensity.     

Ultrafast photodetectors based on the interaction of microwave radiation and a photoexcited plasma in semiconductors

The interaction of microwave radiation with the plasma in photoionized semiconductor photocells (CdS, CdSe) placed in waveguide measurement systems is investigated theoretically and experimentally. The interaction of the characteristic waveguide modes with a photoexcited semiconductor plasma is investigated. The dependence of the reflection coefficient and phase of the microwave radiation on the intensity of the optical radiation to be measured is obtained, and the influence of the surface of the semiconductor photocells on these parameters is investigated. A microwave photodetector design based on a millimeter-wave interferometer is developed. Zh. Tekh. Fiz. 68, 94–98 (November 1998)     

On photoexcitation of baryon antidecuplet

We show that the photoexcitation of the nonexotic members baryon antidecuplet, suggested by the soliton classification of low-lying baryons, is strongly suppressed on the proton target. The process occurs mostly on the neutron target. This qualitative prediction can be useful in identifying the nonexotic members of the antidecuplet in the known baryon spectrum. We also analyze the interrelation between photocouplings of various baryon multiplets in the soliton picture and in the nonrelativistic quark model.Received: 9 April 2003, Published online: 18 November 2003PACS: 13.30.-a Decays of baryons - 13.60.-r Photon and charged-lepton interactions with hadrons - 14.20.-c Baryons (including antiparticles)     

Polarization dependence of photoexcitation in photofield emission

The mechanisms of one-photon photoexcitation in photofield emission have been studied experimentally by measuring the photocurrent from selected crystallographic planes of a tungsten field emitter as a function of the polarization of the incident light. Two distinct components of the photocurrent were identified. The corresponding excitation mechanisms were deduced from the results of the polarization measurements supplemented by band structure considerations. Surface effect emission dominates at large angles of light incidence, and is observed even from within the geometric shadow of the tip. It depends on the light polarization inside the metal in a characteristic way. Indirect bulk photoemission is prominent at small angles of light incidence and is independent of the polarization inside the metal. It is concluded that bulk and surface excitations in photofield emission can be distinguished by appropriately selecting the direction of polarization and the angle of incidence of the incident light.