The form factors of the electron-phonon interaction for GaAs/Ga \V Al V As single heterostructures have been evaluated using a finite height barrier. The calculations are performed within the extreme quantum limit approximation, assuming for the envelope electronic wavefunction a modified Fang-Howard wavefunction. Both types of long-wave phonons, longitudinal optical and interface phonons, are considered. It is found that the effect of the finite height is to reduce the strength of the electron-phonon interaction.
1996 Academic Press Limited
Crystal growth techniques such as molecular beam epitaxy (MBE) and metal-organic chemical-vapor deposition (MOCVD) allow the precise fabrication of atomic-scale semiconductor single heterostructures (HSs) with a wide range of predetermined doping and compositional profiles. The modulation doped HSs are usually typified by a heterointerface between compound semiconductors such as GaAs and Ga \V Al V As. The wider-gap semiconductor Ga \V Al V As (barrier material) is doped with donor impurities (e.g. Si), while the smaller-gap semiconductor GaAs (well material) is nominally undoped. Because of the conduction band discontinuity at the heterointerface, electrons from the donor centers in the Ga \V Al V As layer are transferred into the GaAs layer, where they form a two-dimensional electron gas (2DEG) confined at the heterointerface. The spatial separation of this 2DEG from the parent ionized impurities reduces the scattering by impurities drastically, giving very high carrier mobilities at low temperatures [1]. The high electron mobility transistor (HEMT) is based on this phenomenon.
To investigate the physical properties of the 2DEG in GaAs/Ga \V Al V As HSs, various nonone-electron effects must be included. In polar semiconductors such as GaAs and Ga \V Al V As, the polarization field associated with the long-wave optical lattice vibrations produces a coupling of the 2DEG electrons to the lattice. Therefore, electron-electron and electron-phonon interactions modify both the electron and the phonon systems. These interaction processes play an important role in describing the screening and the transport properties [2-5], the resonant magneto-phonon effects [6-10] and the polaron self-energy [2,[11][12][13].
The effect of the electron-electron interaction (exchange-correlation effects in a local mean field approximation) on the subband energies can be investigated using the density-functional method. This method was applied successfully to calculate the electronic subbands of polar semiconductor HSs and insulator-Si interfaces [14,15].
The heterointerface of GaAs/Ga \V Al V As HSs modifies the spectrum of optical phonons interacting with the 2DEG electrons. Two types of long-wave lattice vibrations appear for these heterostructures: longitudinal optical (LO) and interface (IF) phonons. Wendler et al. [16] have proposed SM ARTICLE 768 Revise 1st proof 22.7.96