Impedance study of undoped, polycrystalline diamond layers obtained by HF CVD

Abstract

passivation layers. These films can be deposited by several techniques, such as Hot Filament Chemical Vapour Deposition (HF CVD), Microwave Plasma CVD (MP CVD), Plasma Jet CVD, or Flame CVD [2].The film characteristics depend on several different deposition process parameters, such as the gas composition and pressure, the substrate temperature, the energy of the impinging ions, etc [3]. The presence of hydrogen in the gas phase promotes the formation of sp 3 C structures but co-deposition of sp 2 carbon phase, as detected by Raman spectroscopy, also takes place [4].Due to its superior physical and chemical properties, diamond can be used as an electronic or optoelectronic material because of its high Johnson and Keyes figures of merit values [5]. However, the electrical and optical properties of diamond films strongly depend on the film preparation conditions. Compared with natural diamond, CVD diamond is usually polycrystalline and contains various defects produced during the deposition procedure. Therefore, it is necessary to establish the relationship between the preparation conditions and the structural and electrical properties of diamond films for electronic or optoelectronic applications.In general, polycrystalline diamond films can be considered as composed from diamond microcrystals oriented in different direction with respect to the substrate surface. The quality of diamond layers increases as the grain size increases starting from the substrate nucleation side to the top of the diamond layer [6].The larger grains induce a decrease of GB phase in the film what results that diamond layer will have smaller content of the sp 2 -hybridized carbon phase. The sizes of grain boundaries and thus concentration of sp 2 carbon phase eventually can lead to limitations in electronic performances of polycrystalline diamond layers. AbstractIn this paper, we report results of impedance measurements in polycrystalline diamond films deposited on n-Si using HF CVD method. The temperature was changed from 170 K up to RT and the scan frequency from 42 Hz to 5 MHz. The results of impedance measurement of the real and imaginary parts were presented in the form of a Cole-Cole plot in the complex plane. In the temperatures below RT, the observed impedance response of polycrystalline diamond was in the form of a single semicircular form. In order to interpret the observed response, a double resistor-capacitor parallel circuit model was used which allow for interpretation physical mechanisms responsible for such behavior. The impedance results were correlated with Raman spectroscopy measurements.

Electrical properties and Mott parameters of polycrystalline diamond films synthesized by HF CVD method from hydrogen/methanol gas mixture

“…Spectroscopic impedance study of nanocrystalline diamond films performed by Ye et al [17] and by Paprocki et al [29] identified the grain interior and grain boundary contributions to the electrical conductivity of the diamond films. At temperatures below 250°C they observed a single semicircular response of the Cole-Cole plots attributed to the diamond grain interior.…”