Regensburg 2004 – scientific programme
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HL: Halbleiterphysik
HL 27: GaN: Pr
äparation und Charakterisierung
HL 27.12: Talk
Wednesday, March 10, 2004, 18:00–18:15, H15
Temperature dependence of the built-in electric field strength in AlGaN/GaN Heterostructures grown on Si(111) — •A.T. Winzer1, R. Goldhahn1, G. Gobsch1, A. Dadgar2, A. Krtschil2, H. Witte2, and A. Krost2 — 1Institute of Physics, TU Ilmenau, 98684 Ilmenau — 2Institute of Experimental Physics, Otto-von-Guericke University Magdeburg, 39016 Magdeburg
Previous studies of the barrier electric field strength F of AlGaN/GaN heterostructures grown on sapphire revealed a strong temperature dependence. This was attributed to the change of piezoelectric polarization due to the large mismatch of thermal expansion coefficients between the nitride layers and the sapphire.
Here, we report for the first time on similar studies for AlGaN/GaN heterostructures on Si(111)-substrate. The samples were grown by MOCVD with different Al-contents in the top AlGaN layer, utilizing a thin low temperature AlN interlayer for strain reduction.
Hall and C(V) measurements as well as spatially resolved surface potential measurements were carried out in order to determine the density of the 2DEG. In the AlGaN layers, F was determined by analyzing the Franz-Keldysh-Oscillations in photoreflectance spectroscopy. Their energetic splittings indicate that F is nearly independent from the temperature, which can be attributed to a constant piezoelectric polarization and thus to a constant strain state.
This interpretation is corroborated by temperature dependent reflectance measurements. The results are compared with self-consistent conduction band calculations.