Effects of Reactive Ion Etching on Phonon-Electron Interactions in Inalas-Ingaas 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 In0.52Al0.48As-In0.53Ga0.47As 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 for the first time 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. In addition HBr-based reactive ion etching has been performed on these structures, and the effects have been correlated with etch time and bias voltage for structures with different cap layer thicknesses.