Berlin 2005 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 57: Poster IIa
HL 57.17: Poster
Dienstag, 8. März 2005, 16:30–19:00, Poster TU E
Investigation of electronic properties of AlGaN/GaN heterostructures using modulation spectroscopy — •A.T. Winzer1, R. Goldhahn1, G. Gobsch1, A. Dadgar2, A. Krtschil2, H. Witte2, A. Krost2, O. Weidemann3, and M. Eickhoff3 — 1Inst. f. Physik, TU Ilmenau, PF 100565, D-98684 Ilmenau — 2Inst. f. Techn. Physik, Otto-von-Guericke-Universität Magdeburg, D-39016 Magdeburg — 3Walter Schottky Institut, TU München, Am Coulombwall 3, D-85748 Garching
Photoreflectance (PR) and electroreflectance (ER) measurements have been proven the most sensitive tools for determining the electric field strength F in the barrier of AlGaN/GaN heterostructures with a two-dimensional electron gas (2DEG).
We present a comparative study of both methods applied to samples grown on Si(111) with different Al-contents and semitransparent Pt Schottky gate contacts. A strong deviation of F between the as grown surface (PR) and the gated area (ER) was found, which originates in the increase of band bending below the Schottky contact. Similarly, the determined 2DEG density has reduced from 4.7x1012 cm−2 (PR) to 2.8x1012 cm−2 (ER), as confirmed by C-V and Hall measurements. Temperature dependent measurements (5 K <T< 300 K) verify the influence of strain (piezoelectric polarization) on F.
2DEG depletion by negative gate bias provides the possibility to study the GaN free excitons, whereas band filling effects (Burstein-Moss shift) can be observed when the gate potential is increased.