FTDLTS: a novel isothermal DLTS method using Fourier transforms

A novel isothermal method of analysing the deep impurity levels in semiconductors is proposed. In this method, named FTDLTS (Fourier transform deep-level transient spectroscopy), the transient junction capacitance, whose waveform is considered as a multi-exponential, is decomposed using two Fourier transforms. The FTDLTS spectrum is fitted by a sum of Gaussians using the least-squares method. The numerical calculus of Fourier transforms and the automatic computer-driven setting up of the FTDLTS method are described. On the basis of the same synthetic signals with and without noise, the FTDLTS spectra are compared with those of two conventional DLTS methods. Because of its better time constant resolution, the FTDLTS method allows correct characterization of deep centres with closely spaced levels. Application to an oxygen multi-implanted 650 degrees C annealed GaAs sample is described.