Far-infrared magneto-absorption of donor-bound excitons in germanium: Pseudo-acceptor model

The magneto-oscillatory absorption spectrum of the arsenic-bound excitons in germanium observed at 118.6 μm reveals a series of absorption lines similar to the Zeeman spectrum of the acceptor impurity. This fact indicates that the bound excitons have the excited states associated with the light-hole Landau ladders and these excited states can be described by the model of a hole bound to the D^- state, i.e. the pseudo-acceptor model. The hole binding energy of the ground state of the bound excitons has been obtained to be 4.7 meV, which is smaller compared with the binding energy of the acceptor impurity.     

Optical orientation and alignment of excitons in quantum dots

Optical orientation and alignment of excitons in InAlAs quantum dots in the AlGaAs matrix have been studied both theoretically and experimentally. Experiments performed in a longitudinal magnetic field (Faraday geometry) reveal transformation of optical orientation to alignment and alignment to orientation, which is caused by exchange splitting of the dipole-active exciton doublet and allowed by the quantum-dot low symmetry. A comparison of theory with experiment made with inclusion of the anisotropy of exciton generation and recombination along the and [110] axes permits one to determine the character of dipole distribution in direction for resonant optical transitions in the self-organized quantum-dot ensemble studied. Fiz. Tverd. Tela (St. Petersburg) 40, 858–861 (May 1998)     

Interaction between the exciton and nuclear spin systems in a self-organized ensemble of InP/InGaP size-quantized islands

Magnetic interaction between spin-polarized nuclei and optically oriented excitons in a self-organized ensemble of size-quantized InP islands in an InGaP matrix has been studied in a magnetic field in Faraday geometry. The effective magnetic fields generated by polarized nuclei at excitons have been measured. The strengths of these fields were found to be different for active and inactive excitons because of the difference between the excitonic g factors. The heavy-hole g factor has been determined. The active and inactive excitonic states were found to be coupled through cross-relaxation. Fiz. Tverd. Tela (St. Petersburg) 41, 2193–2199 (December 1999)     

Optical properties of excitons in semiconductor (InP)-insulator quantum wires

Features in the spectra of absorption, luminescence, and luminescence efficiency obtained under sample excitation with differently polarized laser radiation, and the nonlinear dependence of the luminescence intensity on the excitation level are explained as due to excitonic transitions in semiconductor (InP)-insulator (chrysotile asbestos) quantum wires. The measured excitonic-transition energies in the quantum wires are in quantitative agreement with calculations. The calculations took into account both the size quantization in a quasi-one-dimensional structure and the “dielectric enhancement” of excitons (the noticeable increase of the exciton binding energy and of the excitonic-transition oscillator strength associated with the increased attraction between the electron and the hole due to the large difference between the dielectric permittivities of the semiconductor and the dielectric matrix).     

Optical spin orientation of excitons in GaSe under longitudinal magnetic field

The degree of circular polarization of the free-exciton luminescence line has been measured in GaSe excited by circularly polarized light at 4.2 K under longitudinal magnetic field. The result shows that the spin relaxation time of exciton is field-dependent but the spin memory before reaching the exciton ground state is almost unaffected by the applied longitudinal magnetic field.     

Polarization anisotropy of exciton in self-assembled elliptical InP/InGaP quantum dots

Optical anisotropy of self-assembled elliptical InP quantum dots has been investigated in terms of the polarization dependence of excitons. Although large size inhomogeneity is present, two kinds of characteristic quantum dots, which are classified into large and small quantum dots, were found in terms of the polarization anisotropy. We have confirmed that the large quantum dots are more pronounced in the polarization anisotropy, where the degree of linear polarization for the large quantum dots is significantly larger (∼60%) than that for the small ones (∼36%). The effective shape of quantum dots is also estimated by using the size dependence of oscillator strength, which is in agreement with the AFM image. We also suggest that the anisotropy of exciton oscillator strength can be modified via the dipole–dipole interaction between nearest exciton dipoles.     

Multiband calculation of exciton diamagnetic shift in InP/InGaP self-assembled quantum dots

Exciton states in self-assembled InP/In_0.49Ga_0.51P quantum dots subject to magnetic fields up to 50 T are calculated. Strain and band mixing are explicitly taken into account in the single-particle models of the electronic structure, while an exact diagonalization approach is adopted to compute the exciton states. Reasonably good agreement with magneto-photoluminescence measurements on InP self-assembled quantum dots is found. As a result of the polarization and angular momentum sensitive selection rules, the exciton ground state is dark. For in-plane polarized light, the magnetic field barely affects the exciton spatial localization, and consequently the exciton oscillator strength for recombination increases only slightly with increasing field. For z polarized light, a sharp increase of the oscillator strength beyond 30 T is found which is attributed to the enhanced s character of the relevant portion of the exciton wave function.     

Dynamic polarization of nuclei in a self-organized ensemble of quantum-size n-InP/InGaP islands

Dynamic polarization of ³¹P nuclei is observed in a self-organized system of InP islands grown by metalorganic-hydride epitaxy in an InGaP matrix. The polarized nuclei produce an effective magnetic field which acts on the polarization of the excitonic radiation. Optical detection of the magnetic resonance signal from ³¹P nuclei in the crystal lattice of nanosize InP islands is successfully carried out. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 9, 711–714 (10 November 1998)     

Photoluminescence study of the annihilation process of donor-bound excitons in ZnO： observation of quantum mechanical interference

We report a photoluminescence observation of the coupling of donor-bound excitons and longitudinal optical phonons in high-quality ZnO crystals at 5 K. The first-order phonon Stockes line of donor-bound excitons exhibits a distinct asymmetric line shape with a clear dip at its higher energy side, suggesting that quantum mechanical interference occurs during the annihilation of donor-bound excitons. The donor binding energy is determined to be 49.3 meV from spectral featural.     

Interferometric spectroscopy for excitons in InP single quantum dots

Dynamical dephasing processes of an exciton and a charged exciton in single InP quantum dots were studied by using interferometric spectroscopy. Interferometric spectroscopy enabled us to observe with high sensitivity the dephasing of exciton or other exciton complexes in single quantum dots. In order to observe the dephasing of the exciton or exciton complexes, emitted single-photons generated from single InP quantum dots were detected through the Michelson interferometer. The contrast of the interferometric signal due to the exciton and the charged exciton shows non-exponential decay under band-to-band excitation for the GaInP matrix. The band-to-band excitation generates carriers trapped in the matrix and the trapped carriers modulate the energy of the quantum dots because of the quantum-confined Stark effect. Therefore the non-exponential decays are caused by energy fluctuation due to the trap carriers in the long timescale.     

Facile sonochemical synthesis of nanosized InP and GaP

A novel sonochemical method for the preparation of MP (M = Ga, In) nanocrystalline materials has been developed. The procedure consists of the in situ synthesis of sodium phosphide and its subsequent reaction with the appropriate metal chloride using ultrasound. The products were characterized by X-ray powder diffraction, electron microscopy, and energy dispersive X-ray microanalysis (EDX). The choice of solvent and the use of high-power ultrasound are both important in the formation of the products.     

Optical bistability in GaInAsP/InP coupled-circular resonator microlasers

Optical bistability is realized in GaInAsP/InP coupled-circular resonator microlasers, which are fabricated by planar technology. For a coupled-circular resonator microlaser with the radius of 20?μm and a 2?μm-wide bus waveguide, hysteresis loops are observed for the output power coupling into an optical fiber versus the cw injection current at room temperature. The laser output spectra of the upper and lower states of the hysteresis loop indicate that the bistability is related to mode competitions. The optical bistability can be explained as the mode competition between the symmetry and antisymmetry coupled modes relative to the bus waveguide.     

Optical resonance of Frenkel excitons

We investigate theoretically under which conditions a maximal number of (coherent) Frenkel excitons can be created by a coherent light pulse. The Coulomb exchange interaction which tends to decrease that number can be, at least partly, compensated by appropriate detuning.     

半导体微腔中激子的光学效应

文章基于Fabry-Pérot半导体微腔,阐述了新型元激发——激子极化激元的基本概念和微观描述,讨论了其在光学放大器、光学开关和单光子源方面的潜在应用,概述了对其实现Bose-Einstein凝聚的实验研究,最后对将来的发展做了一个简单的展望.     

Optical and thermal orientation of localized excitons in solid solutions under resonant excitation in a longitudinal magnetic field

A theoretical and experimental study of the effect of a longitudinal magnetic field on optical orientation and magneto-circular polarization of the luminescence of localized excitons in semiconducting solid solutions is reported. It is shown that recombination takes place through two types of emitting states differing substantially in the degree of anisotropy, g factor, and spin relaxation time. Estimates are made of the g factors, anisotropic and exchange splittings, lifetime, and spin relaxation time of localized states in a CdS_0.96Se_0.04/GaAs solidsolution epitaxial layer. Fiz. Tverd. Tela (St. Petersburg) 40, 900–902 (May 1998)     

半导体微腔中激子的光学效应

文章基于Fabry-Pérot半导体微腔,阐述了新型元激发--激子极化激元的基本概念和微观描述,讨论了其在光学放大器、光学开关和单光子源方面的潜在应用,概述了对其实现Bose-Einstein凝聚的实验研究,最后对将来的发展做了一个简单的展望.     

Optical detection of triplet excitons in GaS

Optically detected magnetic resonance has been used to investigate exciton recombination in the layered semiconductor GaS. Five triplet exciton resonances have been observed all with the same g-value of g_ex6 = 2.006 ± 0.002 but with different zero field splittings:

$\text{D}{}^{\mathrm{I}}\text{= + 0.013 cm}{}^{\mathrm{?1}}\text{, D}{}^{\mathrm{II}}\text{= + 0.024 cm}{}^{\mathrm{?1}}\text{, D}{}^{\mathrm{III}}\text{= + 0.025 cm}{}^{\mathrm{?1}}$

,

$\text{D}{}^{\mathrm{IV}}\text{= + 0.075 cm}{}^{\mathrm{?1}}\text{, D}{}^{\mathrm{V}}\text{= + 0.010 cm}{}^{\mathrm{?1}}$

. The resonances from the high energy wing are remarkably narrow and we believe that this may be the first observation of resonance from free indirect excitons.     

Optical properties of Si-doped InAs/InP quantum dots

InAs quantum dots (QDs) were grown on InP substrates by low pressure-metalorganic chemical vapor deposition. Disilane (Si₂H₆) was used as an n-type dopant. The positions of Si doping were varied: buffer layer, capping layer, modulation doping, and QD itself. Surface treatment of InP by Si₂H₆ was also performed to see the effect of Si on InAs QD. Photoluminescence (PL) and atomic force microscopy (AFM) were used to characterize optical and structural properties of QDs, respectively. It was found that the PL peak positions varied from 0.73 to 0.88 eV with the position of Si doping. PL peak blue shift in modulation doped sample was explained in terms of state filling effect. It was found that Si doping at QD itself was the most effective way to obtain the strongest integrated PL intensity without degrading the QD size distribution.