Determination of carrier capture cross sections of traps by deep level transient spectroscopy of semiconductors

The conventional method of determining trap capture cross sections by deep level transient spectroscopy (DLTS) of semiconductors involves observing the DLTS peak amplitude as a function of filling pulse duration. Pulses that are inconveniently short and time-consuming experimental measurements may be required. A method is proposed that involves observing the DLTS peak amplitude change as the observation rate window (t₂-t₁) is varied for a fixed-duration filling pulse. This gives consistent results for the capture cross section and its dependence on temperature. Analysis of the technique is given and a comparison between theory and experiment is presented for two electron traps in bulk n-GaAs. For the trap at E_C- 0.215 eV, σ_∞ is 2.3×10^-15 cm² and the activation energy from σ(T)= σ_∞ exp(-E_σ /kT) is 0.116±0.003 eV. For the trap at E_C -0.35 eV, the cross section σ_∞ is 1.0×10^-13 cm² and the activation energy is 0.200±0.025 eV. Large variations of cross section with temperature such as these have been reported in other studies, and are a consequence of lattice relaxation effects.