Near-surface and bulk deep trap states in AlxGa1-xAs/GaAs

We have measured the field-effect deep-level transient spectra of AlxGa1-xAs/GaAs (where x=0.385) at different reverse-bias fields to probe the near-surface deep trap and bulk deep trap states. In the temperature range 77 to 380 K and for a reverse-bias field -1 to -5 V/cm, four major deep traps were identified. The results of our investigation indicate a distinct effect on the deep-level spectra. Three of the deep trap states E1, E2 and E3 showed definite peak enhancement with the applied reverse-bias field and were identified as bulk deep trap states. The fourth deep trap state E4 was a very weak deep trap state and it showed a decrease of the peak height with the applied reverse-bias field. It was labeled as a near-surface deep trap state.