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Register a new userPhotogalvanic effects due to quantum interference in optical transitions demonstrated by terahertz radiation absorption in Si-MOSFETs
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We report on the observation of the circular (helicity-dependent) and linear photogalvanic effects in Si-MOSFETs with inversion channels. The developed microscopic theory demonstrates that the circular photogalvanic effect in Si structures it is of pure orbital nature originating from the quantum interference of different pathways contributing to the light absorption.
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The terahertz spectra of the dynamic conductivity and radiation absorption coefficient in germanium-silicon heterostructures with arrays of Ge hut clusters (quantum dots) have been measured for the first time in the frequency range of 0.3-1.2 THz at room temperature. It has been found that the effective dynamic conductivity and effective radiation absorption coefficient in the heterostructure due to the presence of germanium quantum dots in it are much larger than the respective quantities of both the bulk Ge single crystal and Ge/Si(001) without arrays of quantum dots. The possible microscopic mechanisms of the detected increase in the absorption in arrays of quantum dots have been discussed.
We report on the observation of the magneto-photogalvanic effect (MPGE) due to inter-subband transitions in (001)-oriented GaAs quantum wells. This effect is related to the gyrotropic properties of the structures. It is shown that inter-subband absorption of linearly polarized radiation may lead to spin-related as well as spin independent photocurrents if an external magnetic field is applied in the plane of the quantum well. The experimental results are analyzed in terms of the phenomenological theory and microscopic models of MPGE based on either asymmetric optical excitation or asymmetric relaxation of carriers in k-space. We observed resonant photocurrents not only at oblique incidence of radiation but also at normal incidence demonstrating that conventionally applied selection rules for the inter-subband optical transitions are not rigorous.
We report on the observation of magnetic quantum ratchet effect in metal-oxide-semiconductor field-effect-transistors on silicon surface (Si-MOSFETs). We show that the excitation of an unbiased transistor by ac electric field of terahertz radiation at normal incidence leads to a direct electric current between the source and drain contacts if the transistor is subjected to an in-plane magnetic field. The current rises linearly with the magnetic field strength and quadratically with the ac electric field amplitude. It depends on the polarization state of the ac field and can be induced by both linearly and circularly polarized radiation. We present the quasi-classical and quantum theories of the observed effect and show that the current originates from the Lorentz force acting upon carriers in asymmetric inversion channels of the transistors.
We have calculated the contribution of intersubband transitions to the third order optical nonlinear susceptibility, $chi^{(3)}(omega,omega,omega)$ for nonresonant as well as resonant third harmonic generation and $chi^{(3)}(omega,-omega,omega)$ for nonlinear refraction and absorption. As examples, we consider InAs/AlSb and GaAs/GaAlAs quantum wells. The effects of finite barrier height, energy band nonparabolicity, and high carrier concentrations are included. It is shown that quantum confinement, rather than the band nonparabolicity, is responsible for high values of nonresonant $chi^{(3)}_{zzzz}$. Very high values of $chi^{(3)}_{zzzz}$ are obtained for third harmonic generation and two photon absorption for incident wavelength near 10.6 $mu$m. Intensity dependence of refractive index and of absorption co-efficient is also discussed for intensity well above the saturation intensity. Effective medium theory is used to incorporate the collective effects.
We report on the observation of the terahertz radiation induced circular (CPGE) and linear (LPGE) photogalvanic effects in HgTe quantum wells. The current response is well described by the phenomenological theory of CPGE and LPGE.
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