Longitudinal optic phonon–plasmon coupling in δ-doped metamorphic InAlAs/InGaAs high-electron-mobility transistor structures on GaAs substrates.

InAlAs/InGaAs metamorphic high-electron-mobility transistor structures with different spacer layers on GaAs substrates are characterized by Raman measurements. The influence of In[sub 0.52]Al[sub 0.48]As spacer thickness on longitudinal optic phonon–plasmon coupling is investigated. It is found that the intensity of GaAs-like longitudinal optic phonon, which couples with collective intersubband transitions of two-dimensional electron gas, is strongly affected by the different subband energy spacings, subband electron concentrations, and wave function distributions, which are determined by different spacer thicknesses. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]