Regensburg 2007 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 7: III-V semiconductors I
HL 7.1: Talk
Monday, March 26, 2007, 11:00–11:15, H17
Strain properties of AlN layers grown on different substrates — •Ronny Kirste1, Ute Haboeck1, Axel Hoffmann1, Christian Thomsen1, Barbara Bastek2, Frank Bertram2, Jürgen Christen2, Armin Dadgar2, and Alois Krost2 — 1Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany — 2Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Germany
We present results of micro-Raman investigations on AlN samples grown by MOCVD on silicon and sapphire substrates. Thermal and lattice mismatch lead to a strong tensile strain in case of growth on silicon. Thus, already thin layers tend to relax by cracking. In the vicinity of such cracks we observed a strong shift of the nonpolar E2(high) line. This mode is suitable to probe the strain properties because it is not affected by free carriers or internal electric fields. Converting this shift we found strain gradients of about 1 GPa in 300 nm thick layers and less than 0.5 GPa in thicker films of 1 or 2 µm. Even, at the center of the cracks the AlN layers are not fully relaxed. We will discuss the reasons, therefore, in comparison to AlN samples grown on sapphire. AlN on sapphire is, contrarily to growth on silicon, almost relaxed or slightly and uniformly compressive strained. Apart from cracking good crystal quality is achieved in both cases.