The terahertz radiation associated with optical electron transitions involving donor states in GaAs/AlGaAs quantum wells is investigated under conditions of interband optical excitation. It has been shown that the near-infrared stimulated emission arising at high optical pumping levels as well as impurity compensation can substantially influence on the intensity and spectra of terahertz photoluminescence related to the optical transitions of electrons from the first electron subband and excited donor states to the ground donor states in quantum wells.

This article discusses specific quantum transitions in a few-particle hole gas, localized in a strongly oblate lens-shaped quantum dot. Based on the adiabatic method, the possibility of realizing the generalized Kohn theorem in such a system is shown. The criteria for the implementation of this theorem in a lens-shaped quantum dot, fulfilled in the experiment, is presented. An analytical expression is obtained for the frequencies of resonant absorption of far-infrared radiation by a gas of heavy holes, which depends on the geometric parameters of the quantum dot. The results of experiments on far-infrared absorption in the arrays of p-doped Ge/Si quantum dots grown by molecular beam epitaxy (MBE) with gradually increasing average number of holes in dot are presented. Experimental results show that the Coulomb interaction between the holes does not affect the resonant frequency of the transitions. A good agreement between the theoretical and experimental results is shown.

Terahertz optical transmission of doped Ge/Si quantum dots has been studied. The absence of the lowest interlevel transition energy dependence on the number of holes in the quantum dot is experimentally observed and explained theoretically. Specific geometry of the studied quantum dots allows the implementation of the adiabatic confining potential and, as a result, proves the applicability of the generalized Kohn theorem to such quantum dot systems.

We have experimentally studied the interband photoluminescence spectra of InGaAsSb/AlGaAsSb quantum wells with different well widths and calculated the dependence of the charge carrier concentration participating in radiative recombination on the pumping intensity. The results of theoretical calculations appeared to be in a good agreement with the experimental relationship between the photoluminescence intensity at spectral maxima and the pumping intensity. The resonant Auger recombination involving two holes and one electron and causing a significant decrease in the charge carrier concentration was detected in one of the samples. Recommendations for suppressing the harmful non-radiative Auger recombination were made to increase the operating efficiency of semiconductor injection lasers at wavelengths of about 3µm.

The paper presents the results of an experimental study of impurity-assisted photoluminescence in the far- (terahertz) and near-infrared spectral ranges in n-GaAs/AlGaAs quantum well structures with different well widths under interband photoexcitation of electron–hole pairs. The optical electron transitions between the first electron subband and donor ground state as well as between excited and ground donor states were revealed in the far-infrared photoluminescence spectra. Observation of these optical electron transitions became possible because of the depopulation of the donor ground state in the quantum well due to the non-equilibrium charge carrier radiative transitions from the donor ground state to the first heavy hole subband. The opportunity to tune the terahertz radiation wavelength in structures with doped quantum wells by changing the quantum well width was demonstrated experimentally.

The 16th Russian Youth Conference on Physics of Semiconductors and Nanostructures, Opto- and Nanoelectronics was held on November 24 - 28 at St. Petersburg Polytechnic University.

Surface plasmon polaritons at the n-GaN/vacuum interface are investigated. Experimental studies of terahertz radiation reflection and emission are performed on heavily silicon-doped GaN epitaxial layers grown on sapphire substrates. To provide interaction of THz radiation with the surface plasmon polaritons, a regular grating was fabricated on the outer surface of the epitaxial layer. Study of terahertz radiation emission from the microstructures under lateral electric field shows that the scattering of non-equilibrium surface plasmon polaritons on the grating makes a significant contribution to the radiation intensity.

A new method for determination of minority carrier lifetimes, mobilities and diffusion lengths is demonstrated. From the transient response of long wavelength infrared barrier detectors with a cut-off of 10 micron, the mobility of the minority holes and their lifetime in bulk InAs0.6Sb0.4 at T = 77 K was determined to be 800 cm2 V−1s−1 and 165 ns, respectively.

Time dynamics of photoluminescence intensity was studied in InGaAsSb/AlGaAsSb quantum wells with different compositions of the barrier solid solution and with different width of the quantum wells. The time of charge carrier capture in quantum wells, the energy relaxation times, lifetime related to resonant Auger recombination were estimated.

Minority carrier lifetime and interband absorption in midinfrared range of spectra were measured in InAs/GaSb strained-layer superlattices (SLSs) grown by molecular beam epitaxy on GaSb substrates. The carrier lifetime in 200-period undoped 7 ML InAs/8 ML GaSb SLS with AlSb carrier confinement layers was determined by time-resolved photoluminescence (PL) and from analysis of PL response to sinwave-modulated excitation. Study of PL kinetics in frequency domain allowed for direct lifetime measurements with the excess carrier concentration level of 3.5×1015 cm−3. The minority carrier lifetime of 80 ns at T=77 K was obtained from dependence of the carrier lifetime on excitation power.

Optical mid‐infrared (MIR) gain in n‐doped tunnel‐coupled semiconductor quantum well structures is studied at a sample temperature of 20 K. The structure is excited via the e1‐e3, intersubband transition by an ultrashort MIR pulse and the gain at the e2‐e3 transition frequency is monitored by a second time‐delayed tunable pulse in the MIR. At high pump intensities, even a narrow MIR emission band is found at the e2‐e3 transition frequency.

Terahertz radiation at lateral electric field from stressed GaAs/GaAsN/GaAs structures doped with Be was observed for the first time. The observed radiation is attributed to hole transitions between resonant and localized acceptor states. This is proved with emission spectra and comparative studies of terahertz radiation from unstressed pGaAs/GaAs structures where no resonant states exist.