June 22, 2004
We present an experimental investigation of heavy doping-induced many-body effects such as band gap narrowing(BGN) and Fermi edge singularity(FES) in Al$_x$Ga$_{1-x}$As using photoluminescence(PL) spectroscopy. The band-to-band transition energy shifts to lower energies and FES-like feature in PL spectra grows with increasing electron concentration. We show that FES-like feature is a nonmonotonic function of temperature and excitation intensity. Our data lead us to suggest that a small concentration of nonequilibrated holes is required to enhance the FES-like feature in the PL spectra.
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April 8, 2006
We present an experimental investigation of band-gap shrinkage in n-type GaN using photoluminescence spectroscopy, as a function of electron concentration and temperature. The observed systematic shift of the band-to-band transition energy to lower energies with increasing electron concentration has been interpreted as many-body effects due to exchange and correlation among majority and minority carriers. The band-to-band transition energy also shifts to lower energy with inc...
October 30, 2015
The electronic band structure of the (Ga,Mn)As system has been one of the most intriguing problems in solid state physics over the past two decades. Determination of the band structure evolution with increasing Mn concentration is a key issue to understand the origin of ferromagnetism. Here we present room temperature photoluminescence and ellipsometry measurements of Ga_{100%-x}Mn_{x}As alloy. The up-shift of the valence-band is proven by the red shift of the room temperatur...
November 26, 2002
We study the energy structure of two-dimensional holes in p-type single Al_{1-x}Ga_{x}As/GaAs heterojunctions under a perpendicular magnetic field. Photoluminescence measurments with low densities of excitation power reveal rich spectra containing both free and bound-carrier transitions. The experimental results are compared with energies of valence-subband Landau levels calculated using a new numerical procedure and a good agreement is achieved. Additional lines observed in ...
June 29, 2000
A Fano resonance mechanism is evidenced to control the formation of optical Fermi-edge singularities in multi-subband systems such as remotely doped AlxGa1-xAs heterostructures. Using Fano parameters, we probe the physical nature of the interaction between Fermi-sea electrons and empty conduction subbands. We show that processes of extrinsic origin like alloy-disorder prevail easily at 2D over multiple diffusions from charged valence holes expected by many-body scenarios.
April 14, 2002
We demonstrate strong one dimensional (1-D) many-body interaction effects in photoluminescence (PL) in a GaAs single quantum wire of unprecedented optical quality, where 1-D electron plasma densities are controlled via electrical gating. We observed PL of 1-D charged excitons with large binding energy of 2.3 meV relative to the neutral excitons, and its evolution to a Fermi-edge singularity at high electron density. Furthermore, we find a strong band-gap renormalization in th...
August 22, 2008
The dependences of the maximum and the half-width of near band-edge photoluminescence of semi-insulating undoped GaAs crystals at 77K on the concentration of background acceptor impurities and the level of excitation in the range from 3x1021 to 6x1022 quantum/(cm2/s) are investigated. The observed dependences are explained by formation of the density tails of states as a result of fluctuations of impurity concentration and participation of localized states of the donor impuri...
April 25, 2002
By selective doping (Be) of the well and barrier regions of p-GaAs/AlGaAs structures we have realized the situation where the upper Hubbard band (A+ centers) has been occupied by holes in the equilibrium. We studied temperature behavior of the Hall effect, variable range hopping conductivity and the photoluminescence spectra of the corresponding structures. The experimental data demonstrated that the binding energy of the A+ states significantly increases with respect to 3D c...
June 3, 2011
The results of investigation of bulk GaAs photoluminescence are presented taken from near-surface layers of different thicknesses using for excitation the light with the wavelengths which are close but some greater than the excitonic absorption resonances (so-called bulk photoexcitation). Only the excitonic and band-edge luminescence is seen under the interband excitation, while under the bulk excitation, the spectra are much more informative. The interband excited spectra of...
October 25, 2018
We report the effect of germanium as n-type dopant on the electrical and optical properties of AlxGa1-xN layers grown by plasma assisted molecular-beam epitaxy. The Al content has been varied from x = 0 to 0.66, confirmed by Rutherford backscattering spectrometry, and the Ge concentration was increased up to [Ge] = 1E21 cm-3. Even at these high doping levels Ge does not induce any structural degradation in AlxGa1-xN layers with x below 0.15. However, for higher Al composition...
December 15, 2001
Using angle-resolved photoemission, we have investigated the development of the electronic structure and the Fermi level pinnning in Ga$_{1-x}$Mn$_{x}$As with Mn concentrations in the range 1--6%. We find that the Mn-induced changes in the valence-band spectra depend strongly on the Mn concentration, suggesting that the interaction between the Mn ions is more complex than assumed in earlier studies. The relative position of the Fermi level is also found to be concentration-de...