T. S. Shamirzaev

Millisecond photoluminescence kinetics in a system of direct-bandgap InAs quantum dots in an AlAs matrix

Anomalously long millisecond kinetics of photoluminescence (PL) is observed at low temperatures (4.2–50 K) in direct-bandgap InAs quantum dots formed in an AlAs matrix. An increase in temperature leads to a decrease in the duration of PL decay down to several nanoseconds at 300 K, whereas the integral PL intensity remains constant up to 210 K. In order to explain the experimental results, a model is proposed that takes into account the singlet-triplet splitting of exciton levels in small quantum dots.

Type-I semiconductor heterostructures with an indirect-gap conduction band

In spite of a great number of publications concerned with studies of semiconductor heterostructures, the type-I semiconductor heterostructures, in which the ground electron state belongs to the indirect-gap (X and L) minimums of the conduction band, have remained poorly understood until recently. In this paper, the possibility is discussed of using III–V semiconductor compounds to create type-I semiconductor heterostructures with electron states belonging to the indirect-gap minimums of the conduction band.

High quality relaxed GaAs quantum dots in GaP matrix

A system of GaAs self-assembled quantum dots (QDs) embedded in GaP matrix was studied by means of transmission electron microscopy, steady-state, and transient photoluminescence. Unusually, the QDs are fully unstrained but they have no nonradiative centers introduced by dislocations at GaAs/GaP heterostructure. The band alignment in the QDs is shown to be of type I.A system of GaAs self-assembled quantum dots (QDs) embedded in GaP matrix was studied by means of transmission electron microscopy, steady-state, and transient photoluminescence. Unusually, the QDs are fully unstrained but they have no nonradiative centers introduced by dislocations at GaAs/GaP heterostructure. The band alignment in the QDs is shown to be of type I.

Atomic structure and energy spectrum of Ga(As,P)/GaP heterostructures

The atomic structure and energy spectrum of Ga(As,P)/GaP heterostructures were studied. It was shown that the deposition of GaAs of the same nominal thickness leads to the formation of pseudomorphic GaAs/GaP quantum wells (QW), fully relaxed GaAs/GaP self-assembled quantum dots (SAQDs), or pseudomorphic GaAsP/GaP SAQDs depending on the growth temperature. We demonstrate that the atomic structure of Ga(As,P)/GaP heterostructures is ruled by the temperature dependence of adatom diffusion rate and GaAs-GaP intermixing. The band alignment of pseudomorphic GaAs/GaP QW and GaAsP/GaP SAQDs is shown to be of type II, in contrast to that of fully relaxed GaAs/GaP SAQDs, which have the band alignment of type I with the lowest electronic states at the indirect L valley of the GaAs conduction band.

Manganese-related recombination centers in epitaxial GaAs grown from a bismuth melt

The photoluminescence properties of heavily doped GaAs:Mn layers grown for the first time by liquid-phase epitaxy from a bismuth melt have been studied. Manganese-related centers of radiative and nonradiative recombination, in addition to the manganese substitutional acceptors (manganese replacing gallium), have been observed in this material. It is found that the concentrations of both centers increase with the doping level. A radiative recombination center with strong electron-lattice coupling has been observed for the first time. We believe that the high concentration of this new center may be a result of the growth method used. The ionization energy of this center is found to be equal to 41 meV.

Room temperature 1.5 μm light-emitting silicon diode with embedded β-FeSi2 nanocrystallites

Light-emitting silicon diode structures with embedded β-FeSi2 nanocrystallites have been fabricated using solid phase epitaxy and a combination of reactive deposition and solid phase epitaxy. Electroluminescence (EL) of the structures was studied over various temperatures and current densities under forward and reverse biases. The structures with nanocrystallites formed by the combined method exhibited EL at temperatures below 70 K only, suggesting the presence of a high concentration of defects—non-radiative centers. High-quality defect-free structures with nanocrystallites formed by solid phase epitaxy revealed intensive room temperature EL in energy range 0.76–1.08 eV at current densities as low as 1 A/cm2.

Nonradiative energy transfer between vertically coupled indirect and direct bandgap InAs quantum dots

Nonradiative energy transfer from indirect bandgap InAs/AlAs quantum dots (QDs) to direct bandgap InAs/AlGaAs QDs was studied by steady-state and transient photoluminescence. We demonstrate that long excitonic lifetime in donor InAs/AlAs QDs allows one to extend the efficient exciton energy transfer between coupled QDs to distances up to 9 nm.

Strong sensitivity of photoluminescence of InAs/AlAs quantum dots to defects: evidence for lateral inter-dot transport

The low-temperature steady-state and time-resolved photoluminescence (PL) from self-assembled InAs quantum dots (QDs) embedded in AlAs with various densities of growth-induced defects has been studied. In contrast to the system of InAs/GaAs QDs, a drastic decrease of the QD PL intensity and decay duration with the formation of relaxed dislocated clusters was observed. It is shown that this strong difference in the luminescence properties of the InAs/GaAs and InAs/AlAs QD systems arises from the very large exciton lifetimes in InAs/AlAs quantum dots, which are longer than the energy transfer time from the QDs to the nonradiative recombination centres of the dislocated clusters.

Ge/Si waveguide photodiodes with built-in layers of Ge quantum dots for fiber-optic communication lines

The results of research aimed at the development of high-efficiency Ge/Si-based photodetectors for fiber-optic communication applications are reported. The photodetectors are designed as vertical p-i-n diodes on silicon-on-insulator substrates in combination with waveguide lateral geometry and contain Ge quantum-dot layers. The layer density of quantum dots is 1×1012 cm−2; the dot size in the plane of growth is ∼8 nm. Unprecedentedly high quantum efficiency suitable for the range of telecommunication wavelengths is attained; specifically, in the waveguides illuminated from the end side, the efficiency was as high as 21 and 16% at 1.3 and 1.55 µm, respectively.

Novel self-assembled quantum dots in the GaSb/AlAs heterosystem

Novel self-assembled quantum dots (QDs) in the GaSb/AlAs heterosystem were obtained and studied by means of transmission electron microscopy, steady-state and transient photoluminescence. A strong inter-mixing of both III and V group materials results in the fabrication of quaternary alloy QDs in the AlAs matrix. The QDs have atypical energy structure: band alignment of type I with the lowest electronic state at the indirect X minimum of the conduction band.