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 (T=10 K) and FIR intensity (I=10 mW/cm2), T1=1.2±0.4 ns, several times longer than predicted theoretically. T1 decreases strongly with increasing temperature and FIR intensity, to 20 ps at T=50 K in the linear regime, and to 15 ps at T=10 K and I=2 kW/cm2. © 1995 The American Physical Society.