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HL: Fachverband Halbleiterphysik

HL 25: Poster Session: GaN - Optical Properties & Preparation and Characterization & Devices

HL 25.13: Poster

Monday, March 26, 2012, 16:00–19:00, Poster D

Direct determination of piezoelectric coefficients for GaN by AFM — •Uwe Röder¹, Frank Lipski², Martin Feneberg³, Ferdinand Scholz², and Klaus Thonke¹ — ¹Institute of Quantum Matter / Semiconductor Physics Group, Ulm University — ²Institute of Optoelectronics, Ulm University — ³Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg

For the piezoelectric coefficients of GaN a broad range can be found in literature (d₃₃ = 2 ... 4 pm/V; d₁₅ = 2.9 ...3.3 pm/V). Mostly, these parameters have been determined from polycrystalline thin layers. We present here data obtained on thick semi-insulating Fe doped GaN layers grown by HVPE. By applying AC voltages with varying amplitude and frequency to top and bottom contacts, and measuring the elongation of the thick GaN layer with an AFM tip in contact mode and lock-in technique to record the phase-correlated periodic change of the quadrature diode signal, we get a direct measure of the piezoelectric constant d₃₃. We obtain a value of d₃₃ = (2.2 ± 0.3) pm/V. Similarly, d₁₅ could be obtained by recording the shear displacement. Effects of mechanical sample resonances etc. have to be carefully avoided.