CONFINED PHONON MODES AND HOT-ELECTRON ENERGY RELAXATION IN SEMICONDUCTOR MICROSTRUCTURES

The role of confined phonon modes in determining the energy relaxation of hot electrons in low-dimensional semiconductor microstructures is discussed within a dielectric continuum model for the LO phonon confin ement and a long wavelength Frohlich model for the electron-phonon int eraction. Numerical results are provided for the hot-electron relaxati on rate as a function of electron temperature and density for GaAs qua ntum wells and quantum wires by taking into account emission of slab p honon modes. Comparison with existing experimental results shows some evidence for slab phonon emission in intersubband electronic relaxatio n in reasonably narrow quantum wells. It is argued that most experimen ts can be interpreted in terms of an electron-bulk phonon interaction model (i.e. by taking into account the effect of confinement only on t he electrons and assuming the phonons to be the usual bulk three-dimen sional phonons) because a number of important physical processes, such as screening, the hot phonon effect, phonon self-energy correction et c, make it difficult to distinguish quantitatively between various mod els for phonon confinement, except perhaps in the narrowest (< 50 angs trom) wells and wires. Detailed numerical results for the calculated i ntra-subband relaxation rate in GaAs quantum wires are provided within the slab phonon and the electron temperature model, including the eff ects of dynamical screening, quantum degeneracy and non-equilibrium ho t phonons.