PHOTON-ASSISTED TUNNELING IN COUPLED DOUBLE-QUANTUM WELLS

Using different techniques to individually contact two closely spaced electron gases, we study the tunneling characteristics between weakly coupled GaAs quantum wells, with and without resonant far-infrared exc itation. We find that for barriers as thick as 300 Angstrom , the alig nment between the subbands in the wells can be observed as an increase d tunneling conductivity. To study photon-assisted tunneling in our sa mples, we use the cyclotron resonance as a strong, tunable electronic excitation in the far-infrared. When the Landau-level spacing h omega( c) corresponds to the laser energy h omega(L), the carriers are effect ively pumped to higher Landau levels, which leads to a reduced resista nce across the tunnel barrier. This photoconductive signal is ''doubly resonant'' in that it is at maximum when omega(c) coincides with omeg a(L), and at the same time the subbands of the two wells are aligned.