Room-temperature short-period transient grating measurement of perpendicular transport in GaAs/AlGaAs multiple quantum wells

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Abstract
A short‐period transient grating technique with 100 fs resolution is used to study room‐temperature perpendicular transport over nanometer dimensions in GaAs/Al0.3Ga0.7As multiple quantum wells (MQWs) whose barrier widths range from 1.4 to 15 nm. With decreasing barrier width, a transition from transport dominated by thermal over‐barrier hopping to that dominated by tunneling is observed. For the thinnest barriers, measurements are in good quantitative agreement with simple rate equations describing tunneling, and the measured grating decay rates are related to the microscopic tunneling rates. By comparison, for MQWs with thick barriers, the transport shows no barrier width dependence, and a room‐temperature over‐barrier hopping rate is extracted.