Optical control of capacitance in a metal-insulator-semiconductor diode with embedded metal nanoparticles.

This paper describes a metal-insulator-semiconductor (MIS) capacitor with flat capacitance voltage characteristics and a small quadratic voltage capacitance coefficient. The device characteristics resemble a metal-insulator-metal diode except that here the capacitance depends on illumination and exhibits a strong frequency dispersion. The device incorporates Fe nanoparticles (NPs), mixed with SrF, which are embedded in an insulator stack of SiO and HfO. Positively charged Fe ions induce dipole type traps with an electronic polarization that is enhanced by photogenerated carriers injected from the substrate and/or by inter nanoparticle exchange of carriers. The obtained characteristics are compared with those of five other MIS structures: two based on Fe NPs, one with and the other without SrF sublayers. Additionally, devices contain Co NPs embedded in SrF sublayers, and finally, two structures have no NPs, with one based on a stack of SiO and HfO and the other which also includes SrF. Only structures containing Fe NPs, which are incorporated into SrF, yield a voltage independent capacitance, the level of which can be changed by illumination. These properties are essential in radio frequency/analog mixed signal applications.