Escape tunneling out of shallow multiple quantum wells studied by transient four-wave mixing

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Abstract
We demonstrate that transient optical dephasing experiments on electrically biased, shallow multiple quantum wells offer the unique possibility of studying the first step in carrier sweep‐out, namely, the tunneling escape out of the individual quantum wells. We find that the electron tunneling times out of the quasibound n=1 quantum well states into the continuum states lie in the subpicosecond regime at high electric fields. In addition, the experimentally determined escape rate is resonantly enhanced when the quasibound n=1 quantum well state couples with the resonant n=2 continuum state originating from the second‐nearest neighbor well.