Interface traps in the Si/${\mathrm{SiO}}_2$ system have been examined by adapted-junction space-charge methods. Principal photoionization thresholds, observed at 86 K, are $E_v$+0.38 eV for excitation of holes from traps, and $E_c$-0.35 eV and $E_c$-0.8 eV for electrons. These are assigned to the two levels of the $P_b$ center. The photoionization thresholds differ by 0.05–0.1 eV from $P_b$ levels at $E_v$+0.3 eV and $E_c$-0.3 eV, as previously observed by capacitance-voltage (C-V) analysis, deep-level transient spectroscopy, and gated electron-spin resonance (ESR). This suggests a configuration change with electron occupancy, in accord with molecular-orbital calculations. Single-shot measurements of thermal emission rates for holes and electrons in the range 150–185 K show activation energies from 0.29 to 0.36 eV, which are corroborated by deep-level transient spectroscopy. Pulse-train measurements show that capture rates do not exhibit a pronounced temperature dependence. Exponential capacitance transients from emission and capture measurements are discussed with respect to previous C-V and ESR studies which suggested wider $P_b$ levels.

• Received 6 September 1988

DOI:https://doi.org/10.1103/PhysRevB.39.5175