Abstract
Diamond films are candidate for a wide range of applications, due to their wide band gap, high thermal conductivity, and chemical stability. In this report, diamond-based heterojunction diodes (HJDs) were fabricated by growing n-type nanocarbon composite in the form of nitrogen-doped ultrananocrystalline diamond/amorphous carbon (UNCD/a-C:H:N) films onto p-type Si substrates. X-ray photoemission and the Fourier transform infrared spectroscopies were employed to examine the contribution of nitrogen atoms from the gas phase into the deposited films. The results indicate the incorporation of nitrogen atoms into the grain boundaries of UNCD/a-C:H film by replacing hydrogen atoms. The capacitance- (C-V-f), conductance- (G/ω-V-f), and series resistance-voltage characteristics of the fabricated Pd/n-(UNCD/a-C:H:N)/p-Si HJDs were studied in the frequency range of 40 kHz-2 MHz. The existence of interface states (Nss) and series resistance (Rs) were attributed to the interruption of the periodic lattice structure at the surface of the fabricated junction as well as the defects on the (UNCD/a-C:H:N)/Si interface. By increasing the frequency (≥500 kHz), the Nss reveals an almost frequency-independent behavior, which indicates that the charges at the interface states cannot follow ac signal at higher frequency. The obtained results demonstrated that the UNCD/a-C:H:N is a promising n-type semiconductor for diamond-based heterostructure diodes.
Highlights
Carbon is a unique chemical element because it morphs into up to 32 allotropes, such as graphite and diamond, which represent sp2- and sp3-orbital hybridization, respectively
The nitrogendoped ultrananocrystalline diamond (UNCD)/a-C:H:N film revealed an extra peak at 409 eV referring to N1s peak [26], which confirms the incorporation of nitrogen atoms into the UNCD/a-C:H film from the hydrogen/nitrogen ambient gases inside the coaxial arc plasma deposition (CAPD) chamber
The results indicate the incorporation of nitrogen atoms into the grain boundaries (a-C:H:N) and increase the sp2 fractions
Summary
Carbon is a unique chemical element because it morphs into up to 32 allotropes, such as graphite and diamond, which represent sp2- and sp3-orbital hybridization, respectively. Ultrananocrystalline diamond (UNCD) can be doped with nitrogen with low activation energy wherein the n-type conduction primarily related to the grain boundary network [4]. It was found that nitrogen dopants create additional electric conduction paths in UNCD films [5]. Ikeda et al [6] correlated the enhancement of electrical conductivity of nitrogen-doped UNCD films to the enlargement of ordering and fraction of sp2-carbon at the grain boundary. Mertens et al [7] have studied the electrical conductivity of nitrogen-doped UNCD films. Their results suggest that the n-type conduction depends on the structure and volume of the grain boundary
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