Parameter evaluation in automated digital deep-level transient spectroscopy (DLTS)

A method of directly evaluating the activation energy DELTAE, capture cross section sigma, and density N(T) of deep-level traps from the pulsed reverse bias capacitance transient is described. The main advantages of this technique are that it requires only a single temperature scan, and it can resolve nonexponential transients due to closely-spaced energy levels. The test samples used for this paper consisted of Schottky diodes fabricated on nonirradiated and 1-MeV electron-irradiated n-type VPE (vapor-phase epitaxy) GaAs wafers. The well known EL2 trap was identified with DELTAE of 0.81 eV, and sigma(n) of 1.0 x 10(-13) cm2 for the nonirradiated sample. These values were found to be in good agreement with published data using established, conventional DLTS techniques. For the irradiated samples a nonexponential capacitance transient was found in the EL2 range of temperatures. The discussed technique was able to resolve two closely spaced deep levels lying at E(c)-0.81 eV and E(c)-0.84 eV, and with capture cross sections of 1.5 x 10(-13) cm2 and 2.5 x 10(-12) cm2, respectively.