Low Frequency Noise Of NC-SI: H/C-SI Heterojunction Diode

Hydrogenated nanocrystalline silicon (nc-Si:H), Si nanocrystals dispersed in a hydrogenated amorphous Si (a-Si:H) matrix, has attracted much interest due to its great potential in physics as well as the device application. Our group has addressed many issues about the electrical properties of nc-Si:H, including measuring the elemental electrical parameters, such as carrier mobility; researching the novel low-dimension phenomenon, such as resonant tunneling; getting the DC characteristics, such as I-V and C-V curves. However, before nc-Si:H-based optoelectric devices can be utilized, the noise problems should be clarified. The figure-of-merit low-frequency noise (LFN) level directly sets the limits of the performance of devices, and also LFN research can help us understand the microstructure of nc-Si:H due to its sensitivity to the material defects. Nonetheless, the LFN research in nc-Si:H system has not so far been explored.In the present work, we investigate LFN of nc-Si:H/crystalline Si (c-Si) heterojunction diodes that are one of simplest devices made of nc-Si:H, observed by the current noise measurement for both forward and reverse bias at room temperature. The majority of our work is assigned to the following aspects: noise measurement setup (both hardware configuration and software develop),measurement of LFN of nc-Si:H diode and discussion of the underlying mechanism of LFN. LFN measurements were performed on nc-Si:H/c-Si heterojunction diodes for the forward- and reverse-biased current I. The 1/fγnoise withγ~1.3 (for low I) or 0.6 (high I) was observed to dominate the LFN and the noise power spectral density Si showed a power law behavior (Si~Iα,α~2). This quadratic behavior may indicate the 1/fγnoise to stem from carrier number fluctuations mediated by deep trap states (forγ~1.3) or band tail states (γ~0.6) of nc-Si:H. Also, the band tail width of nc-Si:H was estimated to be ~65 meV.This work is supported by the National Major Basic Research Project of 2012CB934302, and Natural Science Foundation of China under contracts 11074169 and 11174202.