Discharge mechanisms modeling in LPCVD silicon nanocrystals usingC–Vand capacitance transient techniques

Charging and discharging phenomena from silicon nanocrystals have been studied by means of capacitance–voltage characteristics on P-type metal-oxide-semiconductor (P-MOS) capacitors with embedded self-assembled silicon quantum dots. The dots have a floating gate behavior as shown by the hysteresis onC –V curves. The Si-dots are charged or discharged by direct tunneling of carriers through a 3 nm thick oxide. The nanocrystals could be charged by electrons or holes, depending on the charging bias conditions. The discharge is studied by constant bias method and shows a logarithmic variation with time. Retention times higher than several hours are observed. A simple model is developed in order to evaluate the electric field within the tunneling oxide layer. Then, complete simulations are done for the different discharge paths. The barrier heights are extracted from the discharge data and possible confinement effects are discussed. The results confirm the high potentiality of silicon nanocrystal-floating gates for memory applications.