Regensburg 2002 – wissenschaftliches Programm
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SYOH: Organische Halbleiter
SYOH 7: Poster
SYOH 7.22: Poster
Montag, 11. März 2002, 18:00–21:00, C
Feedback charge capacitance of organic modified GaAs Schottky diodes — •I. Thurzo, T.U. Kampen, and D.R.T. Zahn — Institut für Physik, Technische Universität Chemnitz, 09107 Chemnitz, Germany
In the feedback charge capacitance method (FCM - [1]) the
capacitance of a diode is probed by a bias pulse δU
≈ kT/q. In response to the pulse there is a charge
increment Δ Q(t) in the outer circuit, consisting of two
components:
ΔQ(t) = ΔQ(0) + Q0[1- exp(-t/τ)].
The FCM capacitance C = ΔQ(t)/ΔU comprises two constituents: the instantaneous capacitance C(0) = ΔQ(0)/ΔU and the No-dqexcessNo-dq capacitance ΔC(t). The study covered n-type GaAs Schottky diodes modified by organic thin films of PTCDA, PTCDI, CuPc and Alq3 between the GaAs substrate and the Ag Schottky gate. The goal has been to provide guidance how to distinguish between dipole polarization, Maxwell dielectric relaxation (τD=ε0εr/σ) and ionization of traps in the organic material, σ being the conductivity. Subsidiary current-voltage and charge deep-level transient spectroscopy [2] measurements are useful when identifying the underlying mechanism of the charging. A comparison of the modifying molecules is presented in terms of the ΔC(∞)/C(0) ratio as obtained from in situ (UHV) and ex situ (air) experiments. [1] T. J. Mego, Rev. Sci. Instrum. 58 (1986), 2798 [2] I. Thurzo and K. Gmucova, Rev. Sci. Instrum. 65 (1994), 2244