OBSERVATION OF RESONANT OPTICAL-PHONON ASSISTED TUNNELING IN ASYMMETRIC DOUBLE-QUANTUM WELLS

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 generate d by electrons during the phonon assisted tunneling. Both the Stokes a nd the anti-Stokes intensities show maxima at a certain applied voltag e, where the calculated subband spacing between the wide and the narro w quantum well states is found to be equal to the LO phonon energy. Th is fact indicates that the population of nonequilibrium LO phonons bec omes maximum when resonant LO phonon scattering occurs. A strong reduc tion in the photoluminescence intensity for the narrow quantum well is also observed at the same bias condition. (C) 1998 American Institute of Physics. [S0021-8979(98)00902-5].