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HL: Halbleiterphysik

HL 4: Ultrakurzzeitph
änomene

HL 4.11: Vortrag

Montag, 8. März 2004, 12:45–13:00, H13

Unipolar impact ionization in GaAs/AlGaAs heterostructures — •O. Schmidt¹, M. Eckardt¹, A. Schwanhäusser¹, G.H. Döhler¹, S. Trumm², M. Betz², F. Sotier², M. Hanson³, and A.C. Gossard³ — ¹Technische Physik I, Universität Erlangen-Nürnberg — ²Physik-Department E11, Technische Universität München — ³Materials Department, UCSB Santa Barbara, USA

Impact ionization and the resulting avalanche multiplication in pin-diodes represent one of the technically most feasible methods for detecting and amplifying small optical signals. The ratio of the electron and hole ionization coefficient α/β determines the ultimate multiplication and noise performance of Avalanche Photodiodes. This study indicated, that the ratio α/β is much higher in a specially designed heterostructure than in a comparable homogeneous AlGaAs-diode.
Our bandgap engineered AlGaAs pin heterostructure allows for spatially selective carrier injection by a wavelength adapted pump pulse. This makes it possible to measure multiplication factors for unipolar initiated transport and deduce the ionization coefficient for electrons and holes, respectively. From steady state experiments we found that in graded band structures the electron ionization coefficient is similar to that of homogeneous structures, whereas the hole coefficient is much smaller.
Our Monte-Carlo calculations are supporting these findings. To gain more information about differences of electron and hole impact ionization with a resolution of fs in time and nm in space, in addition, we are performing two color fs pump and probe experiments.