Optical transmittance of thin GaAs wafers upon laser pumping in the region of exciton resonances and the continuum of states: Exciton-exciton interaction

The transmittance spectra of thin “pure” GaAs bulk wafers upon optical pumping corresponding to the band of the ground state of the exciton series are recorded at a temperature of T = 1.7 K. The wafers were grown by molecular-beam epitaxy and vapor-phase epitaxy. An increase in the line amplitude and width upon pumping is observed, with no noticeable changes in the spectral position of the line peak. The increase is similar to that observed upon pumping in the continuum of states, but occurs at a somewhat lower rate. Estimation of the concentration of excitons created by pumping provides a means for determining the exciton-exciton interaction constant and comparing the result with known data. The integrated absorption method makes it possible to refine the exciton polariton-free charge carrier and exciton polariton-impurity interaction constants. The differential photoabsorption of the samples at the pumping modulation frequency is measured. The resultant modulated absorption spectra demonstrate the connection between induced absorption and the formation of differential spectra.     

Evaluation of the quality of GaAs epitaxial layers and their interfaces from analysis of the exciton absorption spectra

Exciton optical spectra are sensitive to even slight changes in the properties of a solid. The spectra of exciton polaritons can be especially informative, although the spectroscopy of these quasiparticles imposes certain restrictions on the measurement temperature and the quality of the material. Exciton parameters such as the resonance frequency ω _T and damping coefficient Γ may vary under the influence of electric fields, defects present in the crystal, or changes in the chemical composition of the film. If the material characteristics vary along the thickness of the film (the z coordinate), so do the resonance frequency and damping coefficient. Here, the spectra of undoped GaAs layers epitaxially grown on GaAs substrates are investigated at T = 1.7 K. Analysis of the spectra at the exciton absorption edge makes it possible to estimate the “dead-layer” depth, the strength of electric fields, and the concentration of impurities.     

The effect of a “Coulomb well” on the absorption and magnetoabsorption spectra of strained InGaAs/GaAs heterostructures

The optical and magnetooptical properties of strained InGaAs/GaAs quantum-well heterostructures grown by molecular-beam epitaxy were studied at T=1.7 K in magnetic fields B⩽7.5 T. The well-resolved oscillatory structure of the magnetoabsorption spectra makes it possible to reproduce the “fan diagrams” for transitions between Landau levels of the HH1E1 quantum-confined states, taking into account exciton binding energies calculated variationally. Based on these results, reduced cyclotron masses of carriers were calculated for quantum wells with various indium contents. A self-consistent variational solution to the exciton problem in the structure under study shows that for weak type-II potentials the effect of Coulomb localization of the hole leads to a relative increase in the oscillator strength of the LH1E1 exciton transition. In this case the LH1E1 and LH3E1 exciton transitions remain spatially direct and retain a considerable intensity. The calculated splitting of ∼9 meV between these two states in zero magnetic field is found to be in agreement with experiment. The significant oscillator strength of light-hole excitons, along with the observed doublet structure, are experimental confirmations that electron-hole attraction can transform a rather low barrier for light holes in a type-II structure into a quantum well with a parabolic “Coulomb” shape near its bottom, i.e., a “Coulomb well.” Fiz. Tekh. Poluprovodn. 31, 1109–1120 (September 1997)     

Temperature-dependent excitonic absorption in long-period multiple In<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>As/GaAs quantum well structures

Temperature variations in the fundamental absorption edge of long-period In _x Ga_{1 − x} As/GaAs structures are studied for samples with different numbers of quantum wells and similar periods. The quantum wells were close in composition and width. Experimental data are interpreted in the model of exciton-polariton light transfer involving localized excitons in confined structures with a finite number of quantum wells. The experimentally observed low-temperature anomaly of the integrated absorption coefficient is attributed to reemission of resonance localized excitons along a finite chain of quantum wells, with no excitonic transfer. The radiative decay time of an exciton in a single quantum well is estimated from the experimental data. It is demonstrated that, at low temperatures, the major contribution to the width of the experimentally observed absorption line corresponding to the ground heavy-hole exciton state is made by inhomogeneous broadening of the line by the field of potential fluctuations associated with the compositional disorder of the alloy. At low temperatures, the inhomogeneous broadening is much more pronounced than the broadening governed by the true radiative and nonradiative dissipative decay.     

Features of SiO2 Layers Synthesized on Silicon by Molecular Layer Deposition

Semiconductors - The characteristics of silicon-oxide layers deposited by various technological methods are compared. It is shown that the catalytic method for obtaining silicon-oxide layers by...     

Fano effect in the magnetoabsorption spectra of gallium arsenide

The magnetooptic absorption spectra of high-quality homoepitaxial GaAs layers in a magnetic field B up to 7.5 T at T=1.7 K are investigated. It is shown that the Fano effect is involved in the formation of certain lines of the magnetooptic spectrum. The parameters of the phenomenological Fano function are determined. It is shown that polariton effects of the diamagnetic exciton play a significant role in the investigated processes. Fiz. Tekh. Poluprovodn. 33, 19–24 (January 1999)     

Photoablation of thin indium oxide films under the action of a pulsed arf excimer laser

The laser-induced ablation threshold of indium oxide (In₂O₃) films was studied in order to evaluate the possibility of using this material as a photoresist for vacuum ultraviolet lithography. In₂O₃ films with a thickness of about 30 nm were prepared by electron beam cathode sputtering with deposition onto quartz substrates in a rarefied oxygen-containing atmosphere. Then the films were irradiated by 20-ns pulses of an ArF excimer laser operating at a wavelength of λ=193 nm and a variable pulse intensity E _p. For a laser intensity below 30 mJ/cm², the oxide etching rate is negligibly small. As the laser radiation intensity increases above this threshold, the etching becomes more effective due to the development of a thermal ablation component.     

Diamagnetic exciton polariton in the interband magnetooptics of semiconductors

The experimentally observed magnetic-field dependence of the integrated absorption coefficient in Al_0.15Ga_0.85As samples at 1.7 K is interpreted. It is established that the dependence results from the competition of two mechanisms: an increase in integrated absorption due to an increase in the oscillator strength as a result of magnetic-field-induced compression of the exciton wave function and a decrease associated with the magnetic freezing-out of charged scattering centers. An analysis of the integrated absorption shows that diamagnetic exciton polaritons are formed in the samples in a magnetic field.     

Temperature-Dependent Total Absorption of Exciton Polaritons in Bulk Semiconductors

Semiconductors - This paper highlights the temperature factor in the experimental study of total absorption as a method for experimental validation and the study of the exciton–polariton...     

Interaction of polarized light with comb-shaped metal-coated nanostructures

We have studied metal-coated (20-nm-thick gold) periodic grating structures (period T = 350 nm) with a rectangular profile formed on the surface of a GaAs substrate. The spectra of reflection of a linearly polarized light from these gratings have been measured in a wavelength range of 600–1200 nm. A sharp (more than 20-fold) maximum in the polarization contrast has been observed at 720–760 nm. The dependence of this peak on the angle of sample rotation is approximately described by a cos⁶θ function. The formation of contrast and its features are related to the excitation of surface plasmons at the metal-air interface on vertical walls of the grating structure.