Temperature and Intensity Dependence of Intersubband Relaxation Rates from Photovoltage and Absorption

We report intersubband-scattering times (T₁) in a semiconductor heterostructure with intersubband spacing below the LO phonon energy. T₁ is determined by simultaneous measurements of the intersubband absorption and the photovoltage induced by far-infrared radiation (FIR) near the intersubband transition frequency. At the lowest temperature (T0ex0ex=0ex0ex10K) and FIR intensity (I0ex0ex=0ex0ex10mW/cm²), T₁0ex0ex=0ex0ex1.2±0.4ns, several times longer than predicted theoretically. T₁ decreases strongly with increasing temperature and FIR intensity, to 20 ps at T0ex0ex=0ex0ex50K in the linear regime, and to 15 ps at T0ex0ex=0ex0ex10K and I0ex0ex=0ex0ex2kW/cm².