Regensburg 2002 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 3: Heterostrukturen I

HL 3.3: Vortrag

Montag, 11. März 2002, 11:00–11:15, H14

Electron Transport Studies on InGaAs/GaAs QWIPs Using Picosecond Photocurrent Measurements — •Sascha Steinkogler, Harald Schneider, Robert Rehm, Martin Walther, and Peter Koidl — Fraunhofer-Institut für Angewandte Festkörperphysik, Tullastr. 72, D-79108 Freiburg

Quantum well infrared photodetectors (QWIPs) are promising candidates for high speed applications including monitor detectors for pulsed lasers and heterodyne spectroscopy. This potential is due to the fast internal response time of intersubband transitions (< 7 ps). We present our investigations of the time-resolved photocurrent response after optical excitation of InGaAs/GaAs QWIPs by infrared fs-laser pulses (∼ 9 µm). Compared to conventional GaAs/AlGaAs QWIPs, the In-containing material system exhibits a higher gain and therefore a higher photocurrent. We observed two photocurrent components, which correspond to different dynamical processes. The fast component (< 15 ps) of the photocurrent transient is attributed to the drift motion of the optical excited electrons from the quantum wells and the slow component (∼ 1 ns) to the injected photocurrent from the emitter contact, which compensates the space charge caused by the illumination. A numerical analysis of these two components allows us to determine the gain. These gain data are in good agreement with the photoconductive gain obtained from cw-responsitivity measurements. We also present a detailed study of the decay time constant of the different components as a function of the temperature and the bias voltage and compare our results with a model developed by Ershov.