Heterojunction Diodes Comprising p-Type Ultrananocrystalline Diamond Films Prepared by Coaxial Arc Plasma Deposition and n-Type Silicon Substrates

Abstract

Heterojunction diodes, which comprise boron-doped p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films prepared by coaxial arc plasma deposition and n-type Si substrates, were electrically studied. The current–voltage characteristics showed a typical rectification action. An ideality factor of 3.7 in the forward-current implies that carrier transport is accompanied by some processes such as tunneling in addition to the generation–recombination process. From the capacitance–voltage measurements, the built-in potential was estimated to be approximately 0.6 eV, which is in agreement with that in a band diagram prepared on the assumption that carriers are transported in an a-C:H matrix in UNCD/a-C:H. Photodetection for 254 nm monochromatic light, which is predominantly attributable to photocurrents generated in UNCD grains, was evidently confirmed in heterojunctions. Since dangling bonds are detectable by electron spin resonance spectroscopy, their control might be an important key for improving the rectifying action and photodetection performance.

Minority carrier lifetime in ultrananocrystalline diamond/hydrogenated amorphous carbon composite films

“…In our recent studies, we have actually fabricated pn heterojunction diodes comprising UNCD/a-C:H films and Si substrates by PVD methods, and their photodetection performance have been investigated [5,[8][9][10][11]. It has also been clarified that the hydrogen content in UNCD/a-C:H films affect their electrical properties of these diodes [12,13].…”

Near-Edge X-ray Absorption Fine-Structure Study on Hydrogenated Boron-Doped Ultrananocrystalline Diamond/Amorphous Carbon Composite Films Prepared by Coaxial Arc Plasma Deposition

“…It has been experimentally demonstrated that heterojuntion diodes comprising boron-doped UNCD/a-C:H films prepared by physical vapor deposition (PVD) such as pulsed laser deposition (PLD) and coaxial arc plasma deposition (CAPD) and n-type Si substrates exhibit a typical rectification action and photodetection for deep ultraviolet light. 10,11 From the rectifying action of the diodes, it was found that carriers are dominantly transported through GBs and a-C:H. 12 Concerning boron doping for producing p-type conduction, we have reported that hydrogen atoms that terminate dangling bonds at GBs are replaced by boron atoms. 8 In addition, it is well known atomic hydrogen preferentially etches sp 2 bonds during the film deposition.…”

Evidence of hydrogen termination at grain boundaries in ultrananocrystalline diamond/hydrogenated amorphous carbon composite thin films synthesized via coaxial arc plasma

“…Boron-doping in the films will be realized by operating arc discharge by use of a graphite target blended with 1.0 atomic (at.) % boron content, equipped with an arc gun, as similar to a previous study [24]. Since several studies have reported that hydrogenterminated diamond surfaces exhibit week p-type conductions in some kinds of CVD diamonds [37][38][39], it is considered to be preferable for consistent discussion being conducted to prepare the films mentioned above, based on a hypothesis that our films also possess the same or similar conductions.…”

“…sp 3 and sp 2 bonds, which largely affect the physical properties of the films. UNCD / a-C and UNCD / a-C:H films synthesized by CAPD have been studied up to the present, by taking the advantages of conventional diamonds, toward the applications not only to hard coatings [18][19][20][21][22] and thermoelectric conversion elements [23], but also to optoelectronic devices such as photovoltaics [24][25][26][27][28][29][30][31][32][33][34][35][36]. As mentioned above, UNCD / a-C:H films prepared by CAPD include more a-C and/or a-C:H fractions and GBs that would act as generation sources of photo-induced carriers, which might be a cause of extremely large light absorption coefficients excessing 10 5 cm −1 in the photon energy range of 3 to 6 eV [15].…”

“…Actually to date, p-and n-type conductions of the UNCD / a-C:H films by CAPD have been already realized by doping boron [24,25] and nitrogen [28], respectively in experimental conditions, and pn heterojunction diodes have been also fabricated by depositing these films on n- [24] and p-type [28] single-crystalline Si substrates. In recent research, it has been clarified that hydrogenation would be a key factor of an enhancement of photovoltaic performance in these diodes [26,27,33].…”