Sequential resonant tunneling characteristics of AlAs/GaAs multiple-quantum-well structures

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Abstract
The resonant tunneling characteristics of AlAs/GaAs multiple-quantum-well structures are studied using time-resolved photocurrent (PC) as well as static PC and photoluminescence measurements. The high potential barrier formed by Al As allows one to observe resonant tunneling from the ground state (1e) in one well to the first three excited states (2e, 3e, and 4e) in the neighboring well. Pronounced features due to resonant tunneling are observed up to temperatures as high as 260 K. The time-resolved photocurrent exhibits an enhancement of the initial decay under the resonance of electrons. The resonant tunneling times from 1e to 3e and to 4e are derived from the time-resolved photocurrent by using the rate equation of electron transport for a complete sequence of resonant tunneling followed by back-relaxation to 1e. The tunneling times obtained are shorter by a factor of 15 to 20 than the values derived from the theory of tunneling through a single barrier.