A. V. Andrianov

Impurity breakdown and terahertz luminescence in n-GaN epilayers under external electric field

We report on the observation and experimental studies of impurity breakdown and terahertz luminescence in n-GaN epilayers under external electric field. The terahertz electroluminescence is observed in a wide range of doping levels (at noncompensated donor density from 4.5×1016 to 3.4×1018 cm−3). Spectra of terahertz luminescence and photoconductivity are studied by means of Fourier transform spectrometry. Distinctive features of the spectra can be assigned to intracenter electron transitions between excited and ground states of silicon and oxygen donors and to hot electron transitions to the donor states.

Terahertz luminescence in strained GaAsN:Be layers under strong electric fields

The authors report on the experimental studies of terahertz emission from strained GaAsN∕GaAs microstructures doped with beryllium at the conditions of electric breakdown of the shallow impurity. The terahertz emission spectrum demonstrates several distinctive signatures that are related to spontaneous optical transitions between resonant and localized states of the acceptor. The energy spectrum calculated for the Be acceptor in the GaAsN∕GaAs heterostructure fits reasonably well with the experimentally observed peaks.The authors report on the experimental studies of terahertz emission from strained GaAsN∕GaAs microstructures doped with beryllium at the conditions of electric breakdown of the shallow impurity. The terahertz emission spectrum demonstrates several distinctive signatures that are related to spontaneous optical transitions between resonant and localized states of the acceptor. The energy spectrum calculated for the Be acceptor in the GaAsN∕GaAs heterostructure fits reasonably well with the experimentally observed peaks.

Terahertz Emission upon the Interband Excitation of GaN Layers

The experimental observation and study of terahertz photoluminescence upon the steady-state interband excitation of epitaxial n-GaN(Si) layers are reported. The properties of the terahertz emission spectrum and the dependence of the spectrum on temperature and photoexcitation intensity suggest that emission occurs due to the trapping of nonequilibrium electrons at charged donors. In the n-type material at low temperatures, charged donors can be formed as a result of the recombination of nonequilibrium holes with electrons localized at donor centers. The main contribution to terahertz photoluminescence is made by 2P → 1S optical transitions between the first excited state and ground state of the donors. In addition, optical transitions of electrons from the conduction band states to the ground state as well as to the excited states of donors are evident in the terahertz emission spectrum.

Terahertz emission and photoconductivity in n-type GaAs/AlGaAs quantum wells: the role of resonant impurity states

Terahertz emission spectra in a longitudinal electric field and lateral photoconductivity spectra under terahertz illumination have been studied in structures with GaAs/AlGaAs quantum wells (QWs). It is shown that the spectra contain features associated with electron transitions involving resonant impurity states related to the second quantum-well subband. Calculations of the energy spectrum of impurity states and matrix elements of optical transitions made by taking into account various positions of the impurity relative to the QW center confirm the assumptions made.

Terahertz-emission generation caused by new effects in the 6H-SiC natural superlattice

It is demonstrated that the 6H-SiC natural superlattice has two simultaneously electroluminescence channels in the terahertz range: narrow lines at frequencies of 1.6–2.3 THz and broader lines at frequencies of about 3.25 THz. The first channel is formed by transitions between the localized states of the Wannier-Stark ladder in the Bloch oscillation mode in the first conduction miniband at point M of the hexagonal Brillouin zone. The second channel is probably caused by transitions between Wannier-Stark ladders formed by electric-field mixing of degenerate states of the conduction band at point K of the hexagonal Brillouin zone. The conduction-band minimum at point K is higher than that at point M by 100–200 meV.

The intensive terahertz electroluminescence induced by Bloch oscillations in SiC natural superlattices

We report on efficient terahertz (THz) emission from high-electric-field-biased SiC structures with a natural superlattice at liquid helium temperatures. The emission spectrum demonstrates a single line, the maximum of which shifts linearly with increases in bias field. We attribute this emission to steady-state Bloch oscillations of electrons in the SiC natural superlattice. The properties of the THz emission agree fairly with the parameters of the Bloch oscillator regime, which have been proven by high-field electron transport studies of SiC structures with natural superlattices.

Terahertz emission upon the band-to-band excitation of Group-IV semiconductors at room temperature

Terahertz emission upon the band-to-band excitation of Group-IV semiconductors (Si:B and Ge:Ga) at room temperature by a semiconductor laser emitting in the visible range (660 nm) is observed and investigated. It is established that, as the crystal temperature is elevated above room temperature, the emission intensity increases considerably, while the emission spectrum shifts to higher frequencies. The terahertz-emission spectra of germanium and silicon are quite similar to each other. The pump-intensity dependence of the terahertz-emission intensity is nearly linear. The above features make it possible to attribute the observed terahertz emission to the effect of crystal heating by absorbed pump radiation.

First experiments and prospects of intracavity difference -frequency generation of mid/far-infrared and terahertz radiation in diode lasers

Our experimental and theoretical investigations in the field of new semiconductor sources of coherent mid/far-IR radiation based on the intracavity nonlinear mixing of close-in-frequency optical fields in dual-wavelength diode lasers are reviewed. Perspective schemes of quantum-well heterolasers of this kind are considered, and the ways of increasing the power of difference-frequency radiation are suggested, including the use of mode-locked lasers and hybrid surface-emitting grating-outcoupled lasers.

Terahertz generation via intracavity mixing in mode-locked dual-wavelength lasers

We put forward a scheme of the efficient terahertz and mid/far-infrared pulsed generation via an intracavity difference-frequency mixing of lasing fields due to the resonant intersubband and non-resonant bulk nonlinearities in the mode-locked dual-wavelength heterolasers.

Generation of coherent terahertz radiation by polarized electron-hole pairs in GaAs/AlGaAs quantum wells

The generation of coherent terahertz radiation upon the band-to-band femtosecond laser photoexcitation of GaAs/AlGaAs multiple-quantum-well structures in a transverse electric field at room temperature is investigated. The properties of the observed terahertz radiation suggest that it is generated on account of the excitation of a time-dependent dipole moment as a result of the polarization of nonequilibrium electron-hole pairs in quantum wells by the electric field. The proposed theoretical model taking into account the dynamic screening of the electric field in the quantum wells by nonequilibrium charge carriers describes the properties of the observed terahertz signal.