Impact of In Situ Annealing on the Deep Levels in Ni-Au/AlN/Si Metal–Insulator–Semiconductor Capacitors

The impact of in situ annealing on the electrical properties of AlN/(111) p-type silicon metal–insulator–semiconductor (MIS) capacitors is studied by capacitance–voltage (C–V) and deep-level transient spectroscopy (DLTS). It is demonstrated that the in-diffusion of Al leads to an enhanced free hole concentration close to the interface, which becomes more pronounced for the in situ annealed capacitors. This excess doping in the near-surface region yields a strong capacitance freeze-out above 200 K. At the same time, a higher density of near mid-gap hole traps is found in the p-type Si substrate. The fact that the deep-level parameters (activation energy E_T and hole capture cross section σ_p) change after annealing indicates that different types of Al-related complexes or clusters are formed before and after in situ annealing. This is supported by the different trap filling kinetics observed in both cases: while for the as-deposited samples exponential filling is found, typical for point defects, there is a tendency for logarithmic slow filling for the deep hole traps in the annealed capacitor.