Residual-photoconductivity spectra (RPS) are studied for HgTe/CdHgTe quantum-well heterostructures of n- and p-type conduction at T = 4.2 K. RPS is shown to be both positive (an increase in the carrier concentration in the quantum well) and negative depending on the illumination wavelength. The RPS maxima in the sample with n-type conduction in general correspond to the RPS minima in the p-type samples and vice versa. It is found for p-type samples that illumination at specific wavelengths leads to the “freezing” of free carriers in the quantum well (QW) but not to a change in the conduction type. This fact indicates the important role of the built-in electric field in the RPS mechanism; this field is “switched-off” upon QW neutralization.

Spectra of persistent photoconductivity (PPC) in HgTe/CdHgTe quantum well (QW) heterostructures of both n- and p-types have been investigated at T = 4.2 K. PPC is shown to be either positive (increase of carrier concentration in QW) or negative depending on a wavelength of the illumination. As a general trend, PPC maxima in n-type sample correspond to PPC minima in p-type samples and vice versa. It is discovered that in p-type samples the illumination with certain wavelengths results in the freezing out of free carriers in QWs but not in the conversion of the conductivity type. The latter indicates a significant role in the PPC mechanism of the built-in electric field that is switching off at the QW neutralization.

The effects of the residual photoconductivity in HgTe/CdHgTe (013) double quantum-well heterostructures are studied at T = 4.2 K. It is shown that the residual photoconductivity in this system has a bipolar character, i.e., both positive and negative persistent photoconductivity is present depending on the illumination wavelength.

AbstractThe effects of the residual photoconductivity in HgTe/CdHgTe (013) double quantum-well heterostructures are studied at T = 4.2 K. It is shown that the residual photoconductivity in this system has a bipolar character, i.e., both positive and negative persistent photoconductivity is present depending on the illumination wavelength.

Сообщается о наблюдении стимулированного излучения в структурах с двойными квантовыми ямами InGaAs/GaAsSb/GaAs, выращенных на подложке Si(001) с использованием релаксированного Ge-буфера. Стимулированное излучение наблюдалось при температуре 77 K на длине волны 1.11 мкм, т. е. в области прозрачности объемного Si. В аналогичных гетероструктурах, выращенных на подложке GaAs, стимулированное излучение наблюдалось при комнатной температуре на длине волны 1.17 мкм, что открывает перспективы интеграции таких структур в кремниевую оптоэлектронику.

The processes associated with the transfer of excitonic excitations between tunnel-uncoupled quantum wells (QW) and the influence of the local electric field were investigated in AlGaAs/GaAs heterostructures by the method of photoluminescence excitation (PLE) spectroscopy at low (4.2 K) temperature. The variation in the intensity of photoluminescence (PL) from the wider QW under resonant excitation of excitonic transition in the adjacent narrow QW has been observed. The difference in the PL maximum position and intensity of the wider QW under resonance excitation of the narrow one is explained by the influence of quantum-confined Stark effect on the process of exciton recombination.

В гетероструктурах AlGaAs/GaAs методом спектроскопии возбуждения фотолюминесценции исследовались процессы, связанные с переносом экситонных возбуждений между туннельно-несвязанными квантовыми ямами и изменением встроенного электрического поля. Наблюдалось изменение интенсивности сигнала низкотемпературной фотолюминесценции (при 4.2 K) из более широкой квантовой ямы при совпадении кванта энергии лазера накачки с энергией экситонного перехода в узкой яме. Изменение положения максимума и интенсивности фотолюминисценции из более широкой квантовой ямы при возбуждении вблизи экситонных резонансов в узкой квантовой яме объясняется влиянием квантово-размерного эффекта Штарка на процесс экситонной рекомбинации.

We report the observation of stimulated emission in heterostructures with double InGaAs/GaAsSb/GaAs quantum wells, grown on Si(001) substrates with the application of a relaxed Ge buffer layer. Stimulated emission is observed at 77 K under pulsed optical pumping at a wavelength of 1.11 μm, i.e., in the transparency range of bulk silicon. In similar InGaAs/GaAsSb/GaAs structures grown on GaAs substrates, room-temperature stimulated emission is observed at 1.17 μm. The results obtained are promising for integration of the structures into silicon-based optoelectronics.

A multifunction setup for coherent optical spectroscopy with excitation of semiconductor structures in a wavelength interval of 750–1800 nm and a time resolution of about 100 fs is presented. Minor adjustments are needed for the measurements of photoluminescence kinetics, photon echo, and four-wave mixing under excitation of samples using time-correlated series of femtosecond laser pulses. Results of optical experiments are presented.

The time-resolved photoluminescence of GaAs/AlGaAs quantum-cascade structures under intense pulse excitation is studied. Aside from optical transitions between the ground electron and hole states of a system of two tunnel-coupled quantum wells, the photoluminescence spectrum at short times after the excitation pulse exhibits features corresponding to transitions between the excited states of these wells, which are not observed in time-integrated photoluminescence spectra. It is shown that, due to a high pump level, the electron gas is initially strongly heated, which makes it possible to observe band-to-band transitions between both the ground and excited states. Nonequilibrium carriers cool down with a characteristic relaxation time of ∼125 ps.

We present the experimental results of time-resolved photoluminescence spectroscopy in type II GaAs/GaAs0.64Sb0.36 quantum well heterostructures. At moderate optical excitation densities (below 103 W/cm2), we observe blue shift of the photoluminescence peak with increasing pump power which results from band bending at the type II heterointerface due to photo-excited charge carriers. With further increase in the excitation density, the observed peak undergoes red shift accompanied by significant drop in the luminescence decay time (from 10 ns to 1 ns) which is caused by extreme band bending and increasing contribution of type I radiative transitions to the photoluminescence signal.

We experimentally observed an increase in the intensity of photoluminescence from a wider quantum well (QW) when an exciton transition was induced in the neighboring narrower QW separated from the former one by a tunneling-nontransparent AlGaAs barrier. The dependence of the efficiency of the near-field radiative transfer of excitons on the distance between QWs was studied in heterostructures without coincidence of exciton resonances in the adjacent QWs. Theoretical results were qualitatively consistent with the available experimental data.

We report a study into the process of energy transfer between quantum wells divided by 30-nm-thick opaque barriers. It was experimentally observed that the intensity of a photoluminescence signal from a quantum well increased by 15% under resonant excitation of exciton transition in the adjacent quantum well. The quantum wells were 30 nm apart. A radiative mechanism of energy transfer in the near-field region of emitting exciton is proposed. Within this theoretical model, the efficiency of the energy transfer decreases by a power law with greater distance between the quantum wells. The theory is found to be in qualitative agreement with the experimental results.

The spectra and kinetics of the low-temperature interband photoluminescence of epitaxial structures of terahertz quantum cascade lasers is studied under conditions of strong pulsed excitation. Photoluminescence corresponding to transitions between both the ground and excited states of two tunnel-coupled wells is observed at high excitation levels (600 mW; spot diameter ∼200 μm). Kinetic measurements show that the rise and decay times significantly decrease up to the time resolution of the measuring system at wavelengths <770 nm with decreasing photoluminescence observation wavelength.

The type of heterojunction in the GaAs1 − x Sb x /GaAs heterostructure at x = 0.36 is studied by photoluminescence spectroscopy and time-resolved photoluminescence. A GaAsSb/GaAs heterostructure with an Sb fraction of 15%, for which we can confidently state is a type-I heterojunction, was studied for comparison. It was established from the blue shift of the photoluminescence line depending on the excitation power and relaxation time of the photoluminescence signal from the GaAs1 − x Sb x /GaAs quantum well, which was ∼11 ns, that the GaAs1 − x Sb x /GaAs structure at an Sb content of 36% clearly constitutes a type II heterojunction. This was additionally evidenced by the data obtained for structures with an Sb content of 15%, in which case no shift of the location of the photoluminescence line on the pump power was observed, while the relaxation time of photoluminescence in the region of the signal from the quantum well was ∼1.5 ns.

The results of an experimental research of the dependence of photoluminescence (PL) intensity in region about 800 nm for silicon nanoinclusions (quantum dots) obtained by Si ion implantation in SiO2 on the dose of Si ions at two temperatures of an annealing Tann = 1000 and 1100°C are presented. It is established that in both cases the dependences have the shape of the curves with a maximum. For 1100°C the maximum is shifted to the lower dose. The influence of an additional ion doping by the phosphorus on intensity of PL is investigated depending on the dose (concentration) of P and the dose of the silicon at Tann = 1000°C. It is shown, that in all the investigated region of P doses, the presence of P enhances the PL. The degree of the enhancement increases with the P dose, but the rate of the intensity enhancement goes down. With the growth of Si dose at the constant dose of P, the degree of the enhancement decreases. In an approximation of an effective mass, the energy spectra of a quantum dot are calculated at the presence of one or several P atoms for various their arrangement.

Processes occurring when a static transverse electric field is applied to a GaAs/AlGaAs n - i - n heterostructure with single quantum wells and asymmetric tunnel-coupled double quantum wells have been investigated by optical methods. The difference between the energies of exciton transitions for quantum wells of different widths makes it possible to attribute the observed photoluminescence peaks to particular pairs of wells or particular single quantum wells. The local electric field for each quantum well has been determined in terms of the Stark shift and splitting of exciton lines in a wide range of external voltage. A qualitative model has been proposed to explain the nonmonotonic distribution of the electric field over the depth of the heterostructure.

A new possibility for growing InAs/GaAs quantum dot heterostructures for infrared photoelectric detectors by metal-organic vapor-phase epitaxy is discussed. The specific features of the technological process are the prolonged time of growth of quantum dots and the alternation of the low-and high-temperature modes of overgrowing the quantum dots with GaAs barrier layers. During overgrowth, large-sized quantum dots are partially dissolved, and the secondary InGaAs quantum well is formed of the material of the dissolved large islands. In this case, a sandwich structure is formed. In this structure, quantum dots are arranged between two thin layers with an increased content of indium, namely, between the wetting InAs layer and the secondary InGaAs layer. The height of the quantum dots depends on the thickness of the GaAs layer grown at a comparatively low temperature. The structures exhibit intraband photoconductivity at a wavelength around 4.5 μm at temperatures up to 200 K. At 90 K, the photosensitivity is 0.5 A/W, and the detectivity is 3 × 109 cm Hz1/2W−1.

Doping with donor and acceptor impurities is an effective way to control light emission originated from quantum-size effect in Si nanocrystals. Combined measurements of photoluminescence intensity and kinetics give valuable information on mechanisms of the doping influence. Phosphorus, boron, and nitrogen were introduced by ion implantation into Si+ -implanted thermal SiO2 films either before or after synthesis of Si nanocrystals performed at Si excess of about 10 at.% and annealing temperatures of 1000 and 1100 degrees C. After the implantation of the impurity ions the samples were finally annealed at 1000 degrees C. It is found that, independently of ion kind, the ion irradiation (the first stage of the doping process) completely quenches the photoluminescence related to Si nanocrystals (peak at around 750 nm) and modifies visible luminescence of oxygen-deficient centers in the oxide matrix. The doping with phosphorus increases significantly intensity of the 750 nm photoluminescence excited by a pulse 337 nm laser for the annealing temperature of 1000 degrees C, while introduction of boron and nitrogen atoms reduces this emission for all the regimes used. In general, the effective lifetimes (ranging from 4 to 40 micros) of the 750 nm photoluminescence correlate with the photoluminescence intensity. Several factors such as radiation damage, influence of impurities on the nanocrystals formation, carrier-impurity interaction are discussed. The photoluminescence decay is dominated by the non-radiative processes due to formation or passivation of dangling bonds, whereas the intensity of photoluminescence (for excitation pulses much shorter than the photoluminescence decay) is mainly determined by the radiative lifetime. The influence of phosphorus doping on radiative recombination in Si quantum dots is analyzed theoretically.

We present the results of studying the effect of phosphorus and hydrogen ion doping, as well as annealing in a hydrogen atmosphere, on photoluminescence (PL) properties of monolayer nanostructures SiO2:nc-Si formed in the process of high-temperature annealing of thin a-SiO films, which were obtained by the molecular-beam deposition on silicon. The effect of high-temperature posthydrogenation of multilayer system (SiO2:nc-Si)/ Al2O3 prepared by annealing of a-SiO/ Al2O3 nanoperiodic structure is also studied. The a-SiO/ Al2O3 structure was obtained by the alternation of the thermal (for SiO) and electron beam (for Al2O3) vacuum evaporation. It is shown that phosphorus ion doping of the SiO2:nc-Si structure leads to PL enhancement of 750-800 nm band inherent to silicon nanocrystals, and quenching of this band occurs under ion implantation of hydrogen. Posthydrogenation of both kinds of structures by annealing in hydrogen leads to the passivation of defects on nanocrystal/matrix interfaces and, as a result, enhancement of the nc-Si related PL.