Seog-Jin Jeon

Full Color Tunable Photonic Crystal from Crystalline Colloidal Arrays with an Engineered Photonic Stop‐Band

An electrically tunable photonic crystal is developed utilizing crystalline colloidal arrays of high refractive index particles. Through modulation of the refractive index of the particle, and the applied electric field, both the bandwidth and position of the photonic bandgap could be tuned. Full color modulation with high optical quality is achieved, which paves a way to develop a novel reflective display.

Spectral reflectance switching of colloidal photonic crystal structure composed of positively charged TiO2 nanoparticles

We report the tunable photonic crystal behavior of highly concentrated, mildly charged TiO2 nanoparticle colloids under external electric field. Reflectance intensity change at the certain photonic bandgap and its irreversible switching characteristics are observed and discussed. Through computer aided numerical analysis, gradient spacing between charged particles is predicted under electric field, which is well coincidence with experimental results. Also, we report the experimental evidence that the charged nanoparticle can play the role as a major charge carrier in non-aqueous liquid. Its short range moving and stacking on electrode cause the capacitive current flow and charge accumulation like ions in liquid state.

Band bending effect induced by gate voltage on the charge loss behavior of charge trap flash memory devices

We found that the polarity of the gate voltage (Vg) during the retention characteristics for a SiO2/Si3N4/Al2O3 (ONA) stack can affect the charge loss direction, due to band bending. Positive Vg could induce electron de-trapping through Al2O3, while a negative Vg could induce the same through SiO2. Consequently, the charge loss rates exhibited a hairpin curve with Vg. We clearly observed that increases of the SiO2 thickness of the ONA stack induced negative shifts of hairpin curve. This result suggests that the dominant charge loss path could be changed from SiO2 to Al2O3 by increasing the SiO2 thickness without Vg.