A focus of this work is to present a defect-level measurement technique based on the multiple-level-defect analytic solution to differential rate equations [Debuf04a] representing multiple defect levels. These rate equations describe the full set of carrier transitions via the defect levels. It is shown that the new theory yields a more accurate spectroscopic method of multiple-level measurement namely Fundamental Frequency Deep Level Transient Spectroscopy (FFDLTS).

Fourier transform DLTS (FTDLTS) [Weiss88] uses Fourier transforms to decompose the multiexponential decay into a form from which the Fourier coefficients may be evaluated. The component time constants are determined from the coefficients. Laplace Deep Level Transient Spectroscopy (LDLTS) [Dobaczewski94] is a mathematical refinement over the usual Deep Level Transient Spectroscopy, giving better resolution of the spectral peaks. This method requires a calculation of the inverse Laplace transform of the capacitance transient. Both methods produce a linear Arhenius plot the slope of which represents the level depth. This plot may be represented by the linear equation y = mx + b. In the event that the intercept b should have a temperature dependence the slope m traces out a curve instead of a straight line. This temperature dependence can arise from the temperature dependence of the band gap, the effective masses, density of states and the capture cross sections. This curve may amount to a twelve percent error in the evaluation of the slope m with a further three percent from the temperature measurement. The present work addresses this issue by calculating the level depth at constant temperature using both the intercept and the slope. At constant temperature the intercept and the slope are constants.

In order to demonstrate the FFDLTS method of defect analysis the theory presented applies to the single-level-defect and may be extended to multiple levels. The form of the pulsed excitation may be a pulse of light or a voltage pulse applied to a pn junction generating excess carriers of concentration ?n(0) at t=0^+ in the conduction band.

Debuf04a
D. Debuf. J. Appl. Phys.,96:6454, (2004).

Weiss88
S. Weiss and R. Kassing.
Solid State Elect.,31:1733--1742, (1988).

Dobaczewski94
L. Dobaczewski, P. Kaczor, I. D. Hawkins, and A. R. Peaker.

J. Appl. Phys.,76:194, (1994).


The Special Research Centre of Excellence for Advanced Silicon
Photovoltaics and Photonics is supported by the Australian Research
Council's Special Research Centres scheme.