Carriers In Heterostructures Research Articles

Effective Photon Recycling and Super Long Lived Minority Carriers in GaInP/GaAs Heterostructure Solar Cell: A Time-Resolved Optical Study

We present a study of recombination dynamics and lifetimes of minority carriers in a GaInP/GaAs heterostructure single-junction solar cell by using a variable-temperature time-resolved photoluminescence (TRPL) technique. It was found that the minority carriers, i.e., electrons, in the p-type GaInP base layer have super long lifetimes of ∼220 μs under the excitation of nanosecond laser pulses. On the basis of a newly developed model for time-resolved luminescence of a localized-state ensemble [e.g., Z. C. Su and S. J. Xu, Sci. Rep. 7, 13 (2017)], it is revealed that as much as 38% of photons emitted by localized carriers may be involved in the photon recycling in the GaInP base layer. The effective photon recycling is believed to be an important factor that causes the super long lifetime of the minority carriers, and can help reduce the radiative recombination loss of photogenerated carriers in heterostructure based solar cells.

The photocatalytic performance of silver halides – Silver carbonate heterostructures

Abstract The synthesized rod-like Ag2CO3 particles (2–4 × 0.3–0.6 μm, length × diameter) served as a precursor for preparation of the AgX/Ag2CO3 (X = Cl, I) composites by ion exchange method. The various microstructural (X-ray diffraction analysis, transmission electron microscopy, nitrogen adsorption-desorption isotherms) and optical (diffuse reflection spectroscopy) techniques were used for thorough characterization of obtained heterostructures. The enhanced photocatalytic performance of AgX/Ag2CO3 heterostructures in comparison to Ag2CO3 nanorods (NRs) was evidenced using degradation of organic dye methylene blue as a test reaction. Also, the formation of composites improved their stability under long run illumination conditions. The effect of AgX content on photocatalytic activity of the composites were also investigated. The possible photocatalytic mechanism that facilitates efficient separation of photo-formed charge carriers in heterostructures was discussed in terms of the relative energetic of valence and conduction bands.

Local trapping and recombination of charge carriers in heterostructures with Ge nanoclusters

Local trapping and recombination of charge carriers in heterostructures with Ge nanoclusters

Recombination of charge carriers in heterostructures with Ge nanoislands grown on Si(100)

In this paper, the study of the recombination of non-equilibrium charge carriers and determination of recombination mechanisms in Ge/Si heterostructures with nanoislands have been presented. The effects of long-term photoconductivity decay in Ge/Si heterostructures with Ge nanoislands have been found as caused by variations of the electrostatic potential in the near-surface region of Si(100) substrate and spatial separation of electron-hole pairs between localized states of Ge nanoislands and states of wetting layer and Si. It has been shown that the photoconductivity decay depends on the excitation energy and temperature, while Ge nanoislands are Shockley-Read recombination centers with a higher recombination rate as compared with Si.

Resonant enhancement of indirect exchange interaction in semiconductor heterostructures

We present an approach to calculate indirect exchange interaction between paramagnetic ions via free carriers in heterostructures. Unlike well‐known Ruderman–Kittel–Kasuya–Yosida (RKKY) theory the suggested method is not a perturbation theory and thus can be used in the wider variety of cases, especially when resonant effects are important. The method is applied to standard 1D and 2D indirect exchange problems. We further focus on calculation of indirect exchange interaction between two ions mediated by 2D free carriers gas separated by a tunnel barrier. The calculations show that if the ion bound state energy lies within the energy range occupied by the free 2D carriers, the indirect exchange interaction is strongly enhanced due to resonant tunneling and far exceeds what one would expect from the conventional RKKY approach.

Depth resolved cathodoluminescence and microanalysis of ZnCdSe/ZnSe quantum well heterostructures

The novel approaches to study the II–VI-based laser heterostructures using cathodoluminescence and electron probe microanalysis techniques are described in detail. The heterostructures were grown by molecular beam epitaxy on GaAs (001) substrates and consist of bottom and top ZnMgSSe cladding layers and ZnCdSe/ZnSe quantum well embedded in Zn(Mg)SSe/ZnSe graded index waveguide. The microanalysis technique based on the intensity measurements of characteristic X-rays has been applied to determine both the composition of ZnCdSe quantum well layer and its position within heterostructure. The depth resolved cathodoluminescence technique has been applied for the transport studies of electron beam generated carriers in heterostructure. The cathodoluminescence intensity of ZnCdSe quantum well has been measured as a function of electron beam energy. The Monte-Carlo simulations of carrier generation distribution within the heterostructure under electron beam irradiation have been used for fitting of experimental results. It made possible the nondestructive characterization of the multilayer heterostructure to estimate both deficiency and carrier transport length.

Phonon Induced Drag of Charge Carriers in Heterostructures in Magnetic Fields: Limit of Weak Fields

Tle response of a 2D gas of charge carriers of mobility μ in magnetic freld to pulsed phonon beams is considered. Previously we derived a quantum Langevin equation for the centre-of-mass of the carrier gas, which allows us to calculate the time integrated drag current. This formula is studied in the weak magnetic field limit. When the ratio of the cyclotron frequency ωc to the frequency ω of phonons is small and μB < 1, the general formula coincides with the corresponding expression obtained in the frame of the Boltzmann equation with the collision integral independent of B.

The phonon-induced drag of charge carriers in heterostructures in weak magnetic fields

The kinetic description of the response of two-dimensional gases of carriers in a weak magnetic field to pulsed beams of bulk long-wavelength acoustic phonons is presented. It is assumed that a surface element with radius vector r filled with this gas has an elongated form characterized by the unit vector . The component of the time-integrated current density is calculated. This quantity depends on a time characterizing the elastic scattering of carriers by defects and on the cyclotron frequency via dimensionless parameter . Using the obtained formula for the component of time-integrated current density, we calculate suitable response patterns and compare them with results of our experiments for a gas of holes.

Measurement of the effective temperature of majority carriers under injection of hot minority carriers in heterostructures

We propose and demonstrate a purely electrical method for measuring the effective temperature Te of majority carriers under the injection of hot minority carriers. The Te of holes in a thin p-type InGaAs layer, heated by electron injection from an InAlAs layer in a three-terminal lattice-matched heterostructure, was determined by measuring the thermionic emission current of holes over another specially designed InGaAs/InAlAs barrier. At T=77 K, we observed an overheating Te−T of over 50 K, even at moderate injection power levels.

Kinetic confinement of charge carriers in heterostructures and accumulation layers

A new type of electron and hole confinement in semiconductor double heterostructures is discussed. The confinement occurs when the effective mass of charge carriers in the central region is higher than that in the outside regions and it results from a 'kinetic well' produced by the transverse free motion. The calculated density of electron states is similar (but not identical) to that of the potentially confined 2D systems. The effect of an external magnetic field on the system is considered; it is shown that the energies of the kinetically confined states are strongly nonlinear functions of field intensity. Specific structures are described in which the kinetic confinement of electrons or holes would be possible. The kinetic confinement due to band non-parabolicity is also considered and its observation in InAs accumulation layers is reviewed.

Microscopic basis for a sum rule for polar-optical-phonon scattering of carriers in heterostructures.

A fully microscopic model of the carrier-phonon interaction is employed to obtain a sum rule for polar-optical-phonon scattering of carriers in semiconductor heterostructures. In 1989, Mori and Ando, considering diatomic polar semiconductors and using a dielectric continuum model to derive the phonon modes, derived a sum rule for the carrier--polar-optical-phonon interaction in single and double planar heterostructures that related and constrained the partial contribution from each branch of the optical-phonon spectrum to the total interaction. Here again such a sum rule is derived, but this work differs in two important ways: (1) Fully microscopic models of the phonons and the carrier-phonon interaction are employed, and (2) the results are valid for any semiconductor heterostructure regardless of geometry or materials, including alloy and nonpolar constituents. It is demonstrated that this sum rule reproduces the usual scattering-rate result in the bulk-crystal limit. The derivation of this sum rule requires no assumptions about the functional form of the phonon modes; rather it employs only the inherent orthogonality and mathematical completeness of the classical vibrational modes over the crystal-lattice degrees of freedom, relationships valid for any harmonically coupled system of particles. Thus this work provides independent theoretical support for the sum rule of Mori and Ando and extends the sum rule to arbitrary heterostructure geometries and nonmetallic materials.

Self-absorption effects on the radiative lifetime in GaAs-GaAlAs double heterostructures

An analysis is presented of the effects of self-absorption of spontaneously emitted photons on the recombination lifetime of injected carriers in the active region of GaAs-GaAlAs double heterostructures. It is shown that at moderate injection levels (∼100 A/cm2) self-absorption effects may lengthen appreciably the net radiative lifetime of the carriers in heterostructures with thick (?1 μ) active regions. Results of the analysis are in good agreement with data of Ettenberg and Kressel on variation of carrier lifetime with active region thickness. From the analysis it is inferred that the internal quantum efficiency of radiative recombination in the device of Ettenberg and Kressel is greater than 90%.