Experimental evaluation of low-frequency oscillations in undoped GaAs to probe deep level parameters

A new method for characterizing undoped, semi-insulating GaAs is presented. The low-frequency current oscillations on undoped liquid encapsulated Czochralski GaAs substrates are used to determine deep level energies, cross sections, and concentrations. A Fourier transform is used to resolve the various frequency components of the signal. The frequency is seen to vary almost four orders of magnitude in a 50-K temperature range. Plotting the temperature dependence of each frequency component in an Arrhenius plot gives activation energies and cross sections corresponding to the deep levels responsible for the oscillations. It is seen that two closely spaced levels cause the low-frequency oscillations. In addition, this technique allows the determination of trap parameters as a function of electric field at values much less than the critical field for intervalley transfer in GaAs.