5.3 Properties of interface states

5.3 Properties of interface states

Generally there are two types of interface states, the acceptor type and the donor type. An

acceptor type interface state is electrically neutral when it is empty and negatively charged when filled with an electron [16, 18].

A donor type interface state is electrically neutral when it is filled with electron and positively charged when empty [18].

Besides being donor or acceptor, a particular interface state is also characterized by

1) Its precise energy level in the bandgap (eg: eV from the valence band edge)

2) Its spatial location (eg: distance from the drain)

3) Its density (eg: number of states per cm 2 for discrete states)

In MOSFETs, these interface states are also caused by hot carrier impacting on the surface. Interface states are known to cause degradation in device parameters such astransconductance, carrier mobility and threshold voltage and generally reduce device reliability and lifetime [17, 18 and 19].