AC and DC Conductivity of Diamond Layers Grown by HFCVD Methods

W. Bala¹‘² K. Paprocki¹, M. Kuczkowska¹, P. Popielarski¹, K. Fabisiak¹, A. Korcala²

‘institute ofPhysics, Kazimierz Wielki University, Powstańców Wielkopolskich 2, PL 85-072

Toruń, Poland wbala @fizyka, umk.pl

Institute ofPhysics, N. Copernicus University, Grudziądzka 5/7, PL 87-100 Toruń, Poland

Diamond exhibits outstanding semiconductor properties with a wide band gap which is indispensable for use in electronic devices such as high temperaturę transistors and blue light-emitting diodes. One of the key problems in diamond devices fabrication is the doping of electrically active n and p-type doped atoms into diamond produced by CYD. Changes of conductance and capacitance at different frequencies, polarization and temperatures have been observed. The diamond layers deposited by HF CVD are supposed to contain a large amount of defects at present stage of synthesis what would provide an important obstacle if this materiał is used for electronics applications.

This paper considers an AC/DC electrical features and the growth of [100]-oriented diamond film prepared on (001) Si substrates by HFCVD method. SEM and Raman measurements indicated that high ąuality polycrystalline diamond films with [100]-faced structure were obtained. We reported investigation of Al/diamond film/Si/Al heterostructure through current-voltage I (V), conductance- and capacitance- freąuency dependencies (G(f),C(f)) at various temperatures (Thermal Admittance Spectroscopy TAS) The diamond films used in this experiment were grown in Hot Filament Chemical Vapor Deposition (HF CVD) reactor at the pressure of 100 mbar. The flow rate of the hydrogen gas was 100 sccm (standard cubic centimeter per minutę), flow of the nitrogen was about lsccm and that of acetylene was 10 sccm. As substrate n-type silicon wafer of the [100] orientation was used. Before diamond deposition the surface of the substrate was polished with 0,01 mm diamond pastę in order to increase the density of nucleation. During diamond layer growth the substrate temperaturę was heldat800°C.

Measurements were performed in the freąuency rangę from 50Hz to 250kHz. Thermal admittance spectroscopy (TAS) curves have been measured in the temperaturę rangę from 100K to 300K. An equivalent circuit of the structure was proposed. It was found for the samples doped with nitrogen, that incorporated doped atoms induce some levełs of electrically active defects with activation energies at the 0.36 , 0.29 and 0.25 eV. The naturę of observed defects and differences between trapping centres in HFCYD diamond films are discussed.