Phonon-electron interactions in the two-dimensional electron gas in InGaAs-InAlAs modulation-doped field-effect transistor structures studied by Raman scattering

Abstract

Raman scattering by coupled longitudinal optic phonons and two-dimensional electron gas electrons in In0.53Ga0.47As-In0.52Al0.48As δ-doped heterostructures provides a powerful probe of electronic properties in these In-based structures. The two highest frequency modes, of the three coupled electron-phonon modes expected in this system, were observed, with the highest frequency mode being identified in InGaAs-based systems. The large dispersion of this mode makes it a particularly sensitive probe for changes in such properties as carrier concentration and subband energy. For structures with higher carrier concentrations coupling of the longitudinal optic phonon to multiple electron intersubband transitions is resolved. These measurements are particularly useful for heavily doped structures for which room-temperature Hall measurements cannot distinguish channel electrons from those in parallel conduction paths.

Anomalous dispersion with excitation wavelength of longitudinal optical phonon–plasmon coupled modes in n-InGaAs

“…In the intermediate frequency range, the coupled modes have a mixed character. In a ternary alloy with two-mode behaviour there are three coupled modes as a consequence of the existence of separate LO modes associated with each of the two sublattices [2][3][4][5]. The highest frequency mode (L + ) presents a behaviour similar to its binary system counterpart, displaying a rapid upward frequency shift with increasing carrier concentration.…”

“…A third coupled mode, the intermediate frequency coupled mode (IFCM), occurs in the gap between the optical frequencies of the two sublattices. This mode is phonon-like except in the vicinity of the plasma frequency and is labelled as L 0 by some authors [2,3,5].…”