Relaxation Time of Short Wavelength Intersubband Transition in InGaAs/AlAs Quantum Wells

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Abstract
Linear and nonlinear light absorption characteristics of short-wavelength (near-infrared) intersubband transition in InGaAs/AlAs quantum wells are investigated for estimation of the intersubband relaxation time. Linear absorption measurements reveal that the intersubband absorption width is dominated by the inhomogeneous broadening caused by well-width fluctuations. Nonlinear absorption measurement results are analyzed by focusing on the inhomogeneous broadening and probe pulse width, which reveals that the intersubband energy relaxation time is as short as 1–10 ps. The observed relaxation time is of the same order as those of long wavelength (far-infrared) intersubband transitions. This result is expected to be useful for the ultrafast application of short-wavelength intersubband transition.