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HL: Halbleiterphysik

HL 43: GaN: Pr
äparation und Charakterisierung II

HL 43.6: Vortrag

Montag, 7. März 2005, 16:15–16:30, TU P164

Determination of the 2DEG density of an AlGaN/GaN HEMT by electroreflectance spectroscopy — •A.T. Winzer¹, R. Goldhahn¹, G. Gobsch¹, A. Link², M. Eickhoff², U. Rossow³, D. Fuhrmann³, and A. Hangleiter³ — ¹Inst. f. Physik, TU Ilmenau, PF 100565, D-98684 Ilmenau — ²Walter Schottky Institut, TU München, Am Coulombwall 3, D-85748 Garching — ³Inst. f. Techn. Physik, TU Braunschweig, Mendelssohnstraße 2, D-38106 Braunschweig

A method for determination of the 2DEG density of an Al_xGa_1−xN/GaN high electron mobility transistor (HEMT) will be presented. The technique is based on electroreflectance spectroscopy, i.e. on the analysis of the Franz-Keldysh oscillations and the determination of the electric field strength in the AlGaN layer. Another result of the method is the polarization discontinuity between AlGaN and GaN which represents the polarization charge bound at the AlGaN/GaN interface. This property is of fundamental interest for the design of HEMTs.

We have investigated a transistor structure with 23% Al-content in the barrier. Using a Schottky gate contact the 2DEG density was adjusted between 0 and 10¹³ cm⁻². Magnetotransport measurements confirm the precision of our method. Furthermore, our findings indicate a 22% lower polarization discontinuity than theory predicts, taking into account the spontaneous and the piezoelectric contribution [Ambacher et al., J. Phys.: Condens. Matter 14, 3399 (2002)]. The results are discussed in terms of a simple plate capacitor model and by self consistent conduction band calculations.