UV Sensitivity of MOS Structures with Silicon Nanoclusters

Abstract

Selective UV sensitivity was observed in Metal-Oxide-Semiconductor structures with Si nanoclusters. Si nanocrystals and amorphous Si nanoparticles (a-Si NPs) were obtained by furnace annealing of SiO_x films with x = 1.15 for 60 min in N₂ at 1000 and 700 °C, respectively. XPS and TEM analysis prove phase separation and formation of Si nanocrystals in SiO₂, while the a-Si NPs are formed in SiO_1.7 matrix. Both types of structures show selective sensitivity to UV light; the effect is more pronounced in the structure with nanocrystals. The responsivity of the nanocrystal structure to 365 nm UV light is ~ 4 times higher than that to green light at 4 V applied to the top contact. The observed effect is explained by assuming that only short wavelength radiation generates photocarriers in the amorphous and crystalline nanoclusters.

Keywords: MOS; Si nanoclusters; UV; selective sensitivity.

Figure 1

Si 2p core level spectra of a control SiO_x film (a) and of films annealed at 700 °C (b) and 1000 °C (c). The notations Si⁺, Si²⁺, Si³⁺ and Si⁴⁺ are used for the four oxidation states.

Figure 2

Cross-sectional TEM (XTEM) images of a SiO_x (1.15) control sample (a), and annealed at 700 °C (b) and 1000 °C (c) samples. The insets show a HR-TEM image of two crystals (left) and a Fast Fourier Transform of selected Si nanocrystal area (right).

Figure 3

I-V dependencies of c-Si/SiO_x/Al structures annealed at 700 (a) and 1000 ^oC (b) in dark and under illumination with red, green, blue and UV light. The inset figures show dark I-V characteristics in semi-logarithmic scale measured in both directions.

Figure 4

Responsivities at 4 V of structures with Si nanocrystals (red curve) and amorphous Si nanoparticles (blue curve).

Figure 5

I-V dependencies in dark and under warm light and UV illumination measured in lateral configuration on samples annealed at 700 (a) and 1000 °C (b). The inset figures show the same dependencies in semi-logarithmic scale.