Dresden 2003 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 4: GaN: Bauelemente
HL 4.4: Vortrag
Montag, 24. März 2003, 11:15–11:30, BEY/154
Photoreflectance studies of Ga- and N-face AlGaN/GaN heterostructures containing a polarisation induced 2DEG — •Andreas T. Winzer1, R. Goldhahn1, C. Buchheim1, G. Gobsch1, O. Ambacher2, A. Link3, M. Eickhoff3, and M. Stutzmann3 — 1Institute of Physics, TU Ilmenau, PF 100565, 98684 Ilmenau — 2Center for Micro- and Nanotechnologies, TU Ilmenau — 3Walter Schottky Institute, TU Munich
Recently, AlGaN/GaN-based polarisation induced high electron mobility transistors (PI-HEMTs) have become a subject of intense investigations because they are attractive candidates for high voltage, high power operation at microwave frequencies as well as for ion sensitive detectors. For all of these applications, detailed knowledge of layer and surface properties is of fundamental importance. Photoreflectance spectroscopy represents a unique method allowing the determination of electric field strengths in PI-HEMT’s with highest accuracy. We discuss results of those studies for both N- and Ga-face structures grown by plasma-induced MBE. For the Ga-face samples, the AlGaN barrier field strength depends strongly on the alloy composition, the layer thickness, and temperature. The decrease with temperature can be explained by the decreasing polarisation induced surface charge (spontaneous and piezoelectric). For N-face samples, the main information is extracted by analysing the Franz-Keldysh-Oscillation arising from the topmost GaN channel layer. A comparison of experimental data with self-consistent potential calculations allows in addition the determination of the surface barrier height.