Electronic Properties of n-type Al X Ga 1-X As Alloys
- PDF / 166,098 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 92 Downloads / 238 Views
M8.10.1
Electronic Properties of n-type AlXGa1-XAs Alloys A. Ferreira da Silva* and I. Pepe Instituto de Fisica, Universidade Federal da Bahia, Campus Universitario de Ondina, 40 210-340 Salvador, Ba, Brazil H. Haratizadeh and P.O. Holtz Department of Physics and Measurement Technology (IFM), Linköping University, SE-581 83 Linköping, Sweden C. Persson, R. Ahuja and J. Souza de Almeida Condensed Matter Theory Group, Department of Physics, Uppsala University, SE-751 21 Uppsala, Sweden A.G. de Oliveria Departamento de Fisica-ICEX, Universidade Federal de Minas Gerais, 30123-970 Belo Horizonte, MG, Brazil
ABSTRACT
We have investigated, theoretically and experimentally, the reduced and optical bandgap shift of Si-doped AlXGa1-XAs alloys as a function of both the Al composition and the Si concentration. The calculations were carried out within a framework of the many particle random phase approximation with the Hubbard local-field correction, considering electron populations in the conduction minima located at the Γ, X and L-points of the Brillouin zone. The experimental data have been obtained by means of photoluminescence spectroscopy. The theoretical predictions are found to be in good agreement with the experimental results.
INTRODUCTION
The AlXGa1-XAs alloys are recognized as important semiconductor materials for optoelectronic and high-speed digital device developments. The efficiency of these devices is highly dependent on the doping and variation of alloy compositions [1-8]. A characteristic of this scenario is that, varying the Al composition x, i.e., from 0 to 1, the fundamental band-gap Eg,0 of this material changes from GaAs- to AlAs-like gap leading to a crossover composition at about x= 0.4, when it passes from the direct to the indirect band-gap energy where the X-point minim of the conduction band (CB) becomes lower in energy than the minimum at the Γ point [1-10]. Increasing the impurity concentration significantly, here quoted as Si, the electron population in the conduction band minim will, due to many-particle effects, lower the band-gap energy. This shift of the band-gap is strongly dependent on whether it is GaAs- or AlAs-like band-gap [4]. Experiments on doped semiconductors above the critical impurity concentration Nc for the
M8.10.2
metal-nonmetal transition reveal a bandgap shift (BGS) beyond 10% of the bandgap of pure material [1,4,10]. For sufficiently highly doped samples, the Fermi level will raise above the conduction band at the same time the fundamental bandgap will be reduced. These two energy levels are called the optical bandgap and the reduced bandgap, respectively [1]. Both these bandgaps are determined theoretically and experimentally at low temperature in this work. The experimental data are obtained from photoluminescence (PL) spectroscopy. The energy shift of the conduction-band (CB) minimum and of the valance-band (VB) maximum have been calculated as a function of the Al composition x and the ionized Si impurity concentration for AlxGa1-xAs alloys. The self-energies for
Data Loading...
