Dresden 2003 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 4: GaN: Bauelemente
HL 4.6: Vortrag
Montag, 24. März 2003, 11:45–12:00, BEY/154
Femtosecond intersubband dynamics of electrons in AlGaN/GaN high-electron-mobility transistors — •Z. Wang1, K. Reimann1, M. Woerner1, T. Elsaesser1, D. Hofstetter2, J. Hwang3, W. J. Schaff3, and L. F. Eastman3 — 1Max-Born-Institut, Berlin, Germany — 2University of Neuchatel, Switzerland — 3Cornell University, Ithaca, NY, USA
The electron dynamics in the inversion layer of an Al0.8Ga0.2N/GaN high-electron-mobility transistor (GS1282 in [1]), which shows a broad e1–e2 intersubband absorption band near λ = 4 µm, is studied in femtosecond pump-probe experiments. In our experiments, electrons are excited resonantly from the e1 to the e2 subband by 50 fs midinfrared pulses. Probe pulses at the same spectral position monitor the resulting nonlinear transmission change as a function of time delay. After interaction with the sample, the probe pulses are spectrally dispersed. For all detection energies we observe almost identical transients, which show an instantaneous (within the 50-fs time resolution of our experiment) bleaching of the e1–e2 absorption and a subsequent recovery within 180 fs. The amplitude of the bleaching signal does not follow the intensity spectrum of the pump pulses, i.e., no spectral hole is burned. From this we conclude that the homogeneous line width of individual e1–e2 transitions is considerably larger than the spectral width of our probe pulses. The data point to extremely fast (below 50 fs) intrasubband carrier redistribution. The observed ultrafast absorption recovery time of 180 fs is the intersubband relaxation of e2 electrons.
[1] D. Hofstetter et al., Appl. Phys. Lett. 80, 2991 (2002).