Mobility and activation energy of lateral photocurrent of InAs quantum dot layers with ultrafast carrier relaxation

Abstract We determined the lateral mobility of photocarriers and activation energy of the photocurrent (PC) in stacked InAs quantum dot (QD) layers with ultrafast carrier relaxation times and 1.5-μm band absorption. Lateral mobility is one of the important parameters in the application of QD layers to photoconductive antennas operating with 1.5-μm gating light for terahertz (THz) wave detection. The activation energy obtained from temperature dependence of PC spectroscopy is important for elucidating the mechanism, and it is an indicator of the temperature range for antenna operation. The dependence of the mobility on the photocarrier density was evaluated from the dependence on the pump power. The mobility sharply increased from 42 cm2/V･s in the dark to 416 cm2/V･s upon laser illumination and then decreased with the increase in the number of generated photocarriers. The broad PC peak from InAs QD layers at around 1400 nm was continuously monitored in the temperature range of 4–292 K. The activation energy of the PC from the InAs QD layers was evaluated in the temperature range of 159–240 K where the PC significantly increased. In the broad PC peak in the wavelength range of 1200–1600 nm, the activation energy increased from 48 to 62 meV with the wavelength. The PC observed at lower temperatures was not derived considering the thermal escape of electrons, but it was determined through the Auger process. The InAs QD layer with ultrafast carrier relaxation has considerable potential in photoconductive antenna applications for THz wave detection.