Micro-Raman Spectroscopy for Large In-Plane Wave Vector Excitations in Quantum-Well Structures

Abstract

Inelastic light scattering has been used extensively in the past ten years to study phonon properties and electronic excitations in heterostructures, quantum wells and superlattices.¹ Most of the experiments were performed in backscattering geometry normal to the layers or interfaces. This limits the possibilities of exciting in-plane excitations. Due to the high refractive index of GaAs the accessible in-plane wave vector is q_|| = 1.7 10⁵ cm^-1 in the usual backscattering geometry with the exciting laser wavelength in the red spectral range. The dispersion of plasmons in layered 2D-electron systems has been studied, for example, in this limited wave-vector range.² A first extension of the in-plane wave-vector was achieved by a 90° scattering geometry.³ The dispersion of interface phonon-polaritons in a GaAs/ AlAs heterostructure has been studied by Nakayama et al.,⁴ also in a quasi-back-scattering geometry from the (100) surface. Otherwise excitations with large in-plane wave-vectors have been observed under resonance conditions due to wave vector non-conservation.^5,6,7 This, however, does not allow the extraction of detailed information on the dispersion of in-plane excitations.