Origins of 1/f noise in nanostructure inclusion polymorphous silicon films
© Li et al; licensee Springer. 2011
Received: 18 December 2010
Accepted: 4 April 2011
Published: 4 April 2011
In this article, we report that the origins of 1/f noise in pm-Si:H film resistors are inhomogeneity and defective structure. The results obtained are consistent with Hooge's formula, where the noise parameter, α H, is independent of doping ratio. The 1/f noise power spectral density and noise parameter α H are proportional to the squared value of temperature coefficient of resistance (TCR). The resistivity and TCR of pm-Si:H film resistor were obtained through linear current-voltage measurement. The 1/f noise, measured by a custom-built noise spectroscopy system, shows that the power spectral density is a function of both doping ratio and temperature.
Nanostructure semiconductor has been the focus of intense interest in recent years due to their extensive device application [1–6]. It is well known that hydrogenated polymorphous silicon is a nanostructure inclusion material [7–9]. Hydrogenated silicon films commonly exhibit high noise at low frequency (f). This noise has a spectral power density of the type S(f) ∝ 1/f a , where a is known as "1/f noise." However, lower noise materials are important for high-performance semiconductor devices. 1/f noise of amorphous and polycrystalline silicon has captured the attention of researchers in the field of electronics and physics for several decades . Polymorphous silicon film is generally prepared by operating a strong hydrogen-diluted silane plasma source at high pressure and power density . Many efforts have been made concerning the growth process, microstructure, transport, and optoelectronic properties of pm-Si:H films . The results indicate that pm-Si:H films show higher transport properties than a-Si:H, a highly desirable trait for the production of devices, such as solar cells and thin film transistors. To date, pm-Si:H investigations have focused on certain applications, but there is no study devoted to the 1/f noise of such materials except those by our group which have reported the dependence of 1/f noise on the change of material structure of silicon films [13–15]. In this article, we focus on the study of the origins of 1/f noise in pm-Si:H and investigate the influence of boron doping ratio on 1/f noise in pm-Si:H films.
Results and discussions
Structure and electrical properties for different doping ratios in pm-Si:H film
4.24 × 1014
3.54 × 1013
4.23 × 1012
3.85 × 1011
where S v is the noise power density at voltage V, α H is the noise parameter, f is frequency, and N C is the total number of charge carriers in a certain volume involved in noise generation. The total number of charge carriers, determined by Hall measurement, in conjunction with the dimension of the pm-Si:H film resistor, determines the noise parameter α H as a function of frequency. Our experimental results also demonstrate the 1/f noise power scales with the square of bias voltage, which is in agreement with the results of Fine et al. .
For each measured sample here, the values of N C, f, and V 2 are constant. The value of noise parameter α H at 100 Hz is plotted against temperature for different doping ratios as shown in the inset of Figure 5b. The noise parameter α H for the pm-Si:H film resistors in this study is also a function of the squared TCR (αH ∝ β2). It demonstrated that the resistance fluctuation of the film samples also resulted in the variation of noise parameter when the measurement temperature changed dramatically.
The results of this study demonstrated that the origins of 1/f noise in nanostructure inclusion pm-Si:H are the inhomogeneity and the defective structure in the films. The power spectral density of 1/f noise is inversely proportional to boron doping ratio, which is consistent with Hooge's formula. The value of S v/V 2 is constant when the voltage is less than 1 V, demonstrating that resistance fluctuation is not the origin of 1/f noise in pm-Si film resistors in the case of constant temperature. At 100 Hz, the temperature dependence of 1/f noise indicates that the power spectral density and the noise parameter α H are proportional to the squared TCR. It has also been proven that the resistance fluctuation of the film samples also results in the variation of noise parameter when the measurement temperature changed dramatically.
temperature coefficient of resistance.
This work was partially supported by National Science Foundation of China via grant No. 60901034 and 60425101.
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