D. M. Gaponova

Spectra of persistent photoconductivity in InAs/AlSb quantum-well heterostructures

Persistent photoconductivity at T = 4.2 K in AlSb/InAs/AlSb heterostructures with two-dimensional (2D) electron gas in InAs quantum wells is studied. Under illumination by IR radiation (ℏω = 0.6–1.2 eV), positive persistent photoconductivity related to the photoionization of deep-level donors is observed. At shorter wavelengths, negative persistent photoconductivity is observed that originates from band-to-band generation of electron-hole pairs with subsequent separation of electrons and holes by the built-in electric field, capture of electrons by ionized donors, and recombination of holes with 2D electrons in InAs. It is found that a sharp drop in the negative photoconductivity takes place at ℏω > 3.1 eV, which can be attributed to the appearance of a new channel for photoionization of deep-level donors in AlSb via electron transitions to the next energy band above the conduction band.

Infrared lateral photoconductivity of InGaAs quantum dot heterostructures grown by MOCVD

Abstract InGaAs/GaAs quantum dots (QD) multilayer modulation-doped structures for infrared photodetector application were grown by the low-pressure metalorganic chemical vapor deposition. Normally incidence photoconductivity (PC) with a lateral electron transport was observed in samples, when the In supply during the QD formation was varied. At low temperature (near 4 K ) PC peak was observed near 16 μm . With increasing temperature another PC peak appeared near 5 μm .

Type II–type I conversion of GaAs/GaAsSb heterostructure energy spectrum under optical pumping

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.

InGaAsN/GaAs QD and QW structures grown by MOVPE

InGaAsN/GaAs heterostructures were grown by low pressure MOVPE. Their structural and optical properties were investigated. Pseudomorphic InGaAsN/GaAs layers with a band gap as low as 0.9 eV as well as ternary InAsN quantum dot and well structures were fabricated. It was shown that the addition of a few percent of nitrogen during the formation of the InAs quantum dots led to a decrease in their dimensions and density which was also accompanied by a sharpening of their uniformity distribution. An increase of the nitrogen content reduced the lattice mismatch between InAsN and GaAs. This also gave rise to a layer-by-layer growth mode and smooth heterointerfaces. The InAsN/GaAs multiple quantum well heterostructures so fabricated had improved structural quality and demonstrated intense photoluminescence at room temperature. r 2002 Published by Elsevier Science B.V.

Growth of BGaAs layers on GaAs substrates by metal-organic vapor-phase epitaxy

BxGa1−xAs layers were grown on GaAs substrates using low-pressure metal-organic vapor-phase epitaxy. Triethylboron, trimethylgallium, and arsine were used as boron, gallium, and arsenic sources. Optimum growth conditions were selected. The layers were studied using X-ray diffraction, secondary-ion mass spectrometry (SIMS), and photocurrent spectroscopy (PCS). The SIMS results showed a uniform boron distribution over the layer thickness. According to the PCS data, the BGaAs band gap decreases as the boron concentration increases.

The time-resolved spectroscopy of InGaAs/AlGaAs heterostructures with asymmetric funnel-shape quantum wells for near- and mid-IR lasing

The dynamics of interband transitions in InGaAs/AlGaAs heterostructures with funnel-shaped quantum wells, when a narrow and deep well is positioned asymmetrically in wide and shallow ones, has been studied experimentally. These structures have been proposed as a dual-colour laser in mid- and near-IR range simultaneously. The lifetime of electrons in the ground and excited states in the quantum wells has been determined by the time of the photoluminescence intensity decline. The obtained lifetime values allow precise identification of peaks in the photoluminescence spectra and a deep insight into the process of high electron states populating. The experimentally found electron lifetime for the interband transitions corresponds on the order of magnitude with the interband transitions lifetime in GaAs. Analysis of the photoluminescence spectra as well as the time dependence of the photoluminescence intensity decline indicates a possibility of population inversion achievement in these structures under high excitation.

Determination of the heterojunction type in structures with GaAsSb/GaAs quantum wells with various antimony fractions by optical methods

The type of heterojunction in the GaAs1 − xSbx/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 − xSbx/GaAs quantum well, which was ∼11 ns, that the GaAs1 − xSbx/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 sandwich InGaAs/GaAs quantum dot structure for IR photoelectric detectors

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.

Features of GaN Growth Attained by Metal-Organic Vapor-Phase Epitaxy in a Low-Pressure Reactor

The properties of GaN layers grown by metal-organic vapor-phase epitaxy on sapphire substrates at atmospheric and reduced pressures were studied. The surface morphology, crystalline, luminescence, and electric transport properties of these structures were comparatively analyzed. The depth profiles of elements were measured using secondary-ion mass spectrometry. The carrier distribution in heavily doped structures with p-n junctions was analyzed by electrochemical C–V profiling. It was shown that GaN layers grown in a low-pressure reactor feature improved structural, electric, and optical characteristics.

Stimulated emission in heterostructures with double InGaAs/GaAsSb/GaAs quantum wells, grown on GaAs and Ge/Si(001) substrates

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.