Abstract
Laser Raman microscope measurements in asymmetric double quantum wells with coupled narrow and wide quantum wells were performed to observe the nonequilibrium longitudinal-optical (LO) phonons that are generated by electrons during the phonon assisted tunneling. Both the Stokes and the anti-Stokes intensities show maxima at a certain applied voltage, where the calculated subband spacing between the wide and the narrow quantum well states is found to be equal to the LO phonon energy. This fact indicates that the population of nonequilibrium LO phonons becomes maximum when resonant LO phonon scattering occurs. A strong reduction in the photoluminescence intensity for the narrow quantum well is also observed at the same bias condition.
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