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HL: Halbleiterphysik

HL 58: Poster IIb

HL 58.13: Poster

Dienstag, 8. März 2005, 16:30–19:00, Poster TU F

Measurements of the electrical excitation of QH-devices in the real time domain — •G. Vasile^1,2, C. Stellmach¹, and G. Nachtwei¹ — ¹Inst.f.Technische Physik, der TU Braunschweig, Mendelssohnstrasse 2, D-38106 Braunschweig — ²National Institute of Research-Development for Cryogenics and Isotopic Technologies, Str. Uzinei Nr. 4, R-1000 Rm. Valcea, Romania

We have performed real time domain measurements of the electrical excitation on Corbino devices (measured with impedance-matching circuit) in order to determine the excitation and relaxation times. We have used Corbino devices of inner radius R₁=100µm, outer radius R₂=150µm and various mobilities (µ=8× 10⁵ cm²/Vs, µ=1.6× 10⁶ cm²/Vs). A pulse generator send through a high frequency cable rectangular pulses to the Corbino disc and via another high frequency cable the sample response, picked up from a 50 Ω serial resistor with the Corbino disc, is read on the oscilloscope. We have used rectangular shapes of 90-180 ns pulse width, 300 ns pulse period and from 0.2 V up to 1.0 V applied voltages. In this way we were able to determine relaxation times of a few nanoseconds according to previous measurements. The higher voltage the shorter response time due to the fact by increasing the applied voltage, the Landau levels are tilted more and more resulting in smaller tunnelling distance between the initial and final tunnelling states, therefore a higher tunnelling rate and consequently a smaller drift length of electrons. According to the drift model, at constant drift length, the response time of the sample should be inverse proportional to the applied voltage, but our measurements yield another dependence.