Two photon absorption in quantum dot-in-a-well infrared photodetectors

Abstract

Two photon absorption processes in InAs∕In01.5Ga0.85As∕GaAs quantum dot-in-a-well photodetectors are studied using free electron laser excitation. Two photon induced, normal incidence photocurrent, observed in the range of 20–30μm, arises from sequential near-resonant two-step transitions involving electron ground to first excited states in the dot, to quantum well final states. We find a two photon absorption coefficient of β∼1×107cm∕GW at 26.5μm (47meV) and 0.8V applied bias. Second-order autocorrelation measurements exhibit two characteristic time constants of ∼3 and ∼40ps. The latter is associated with the intermediate state electron lifetime, whereas the short decay is explained by the involvement of acoustic phonon assisted transitions.

The transition mechanisms of quantum-dot/quantum-well mixed-mode infrared photodetectors

“…In this case, transition (b) would be dominant for the devices negatively biased such that the 5.3 lm response would be observed. Assuming that the Fermi level of the device are lower than the E WL state, the observed LWIR response of the device is attributed to the two-photon absorption with E WL and E 0,QW as the intermediate states [9]. Therefore, dominant transitions of (c) E 0,QW -E 1,QW and (d) E WL -E 1,QW would be observed for the device at positive and negative biases, respectively.…”

Photo and dark current noise in self-assembled quantum dot infrared photodetectors

“…Quantum dot infrared photodetectors have attracted more and more attention in the last years since they are expected to reach higher gains and exhibit lower dark current than QWIPs. Furthermore they are sensitive to normally incident infrared radiation not requiring special optical coupling [1][2][3][4][5][6][7][8][9][10].…”

Injector Quantum Dot Molecule Infrared Photodetector: A Concept for Efficient Carrier Injection

“…The probability of such a transition increases with temperature. In principle it does not make a large difference if the electrons are injected into the GS or the p-state, because once the electrons are injected into higher EXs of QD2 the electrons can further relax towards ground-state within a relatively short time-range of 30∼60 ps [41].…”