Optical saturation of mid-infrared transitions in self-assembled InAs quantum dots: evidence for an LO phonon bottleneck

Summary form only given. We present experimental observation of the saturation of mid-infrared transitions of electrons out of the dots (IR photoconductivity). The existence of this saturation means that charge carriers survive in the excited state at least as long as their characteristic time for tunneling out of the dot region, thus setting a lower limit on the lifetime of the carriers in the excited state. This lifetime is estimated to be (on average) in excess of 15 picosecond, indicating that LO phonon emission has indeed been suppressed.