Density of states distribution in diamond thin films

Mort, J.; Machonkin, M. A.; Okumura, Kazuki

doi:10.1063/1.105461

Cited by 41 publications

(12 citation statements)

References 14 publications

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“…Previous authors have assigned such phenomena in undoped CVD diamond to the band of shallow hole traps centered at an energy approximately 0.61 eV from the valance band. 2,3 In contrast, photocurrent measurements from coplanar detectors using 4 When illuminated with long pulses of UV light, coplanar diamond detectors also demonstrate significant photocurrent persistence. 5 In one study using 200 nm irradiation from a deuterium lamp, a clear dependence was observed between photocurrent decay times and the nature of the metaldiamond contact structure.…”

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confidence: 97%

Performance of a diamond x-ray sensor fabricated with metal-less graphitic contacts

Sellin

Galbiati

2005

Applied Physics Letters

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We report the x-ray photocurrent response of a coplanar chemical vapor deposition diamond detector fabricated using a metal-less graphitic ohmic contact. Ion implantation of 70 keV boron ions to a dose of 2 ϫ 10 16 cm −2 was performed through a patterned photoresist to produce a coplanar graphitic contact structure. The device photocurrent showed a fast response to pulsed x-ray irradiation, and showed no evidence of photocurrent persistence that is observed in devices fabricated using metal Schottky contacts. The graphite-contact device also showed no extrinsic photoconductivity when illuminated with white light. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.2035885͔Chemical vapor deposition ͑CVD͒ diamond has considerable potential for use as a radiation sensor, particularly for deep ultraviolet ͑UV͒ and x-ray detection. Various authors have reported investigations of coplanar CVD diamond detectors as a tissue equivalent radiation dosimeter, and have demonstrated an x-ray photocurrent sensitivity similar to that of silicon photodiodes. The unique properties of diamond are well suited for this application, including extreme radiation hardness, high resistivity, and good charge transport. However the development of practicable diamond x-ray detectors has been restricted by a combination of priming effects and slow time response, or photocurrent persistence. These effects are due to a complex interplay between bulk trapping centers inherent in CVD material and the nature of the metaldiamond ohmic contacts used to fabricate the devices. In this work, we describe the performance of a coplanar x-ray sensor fabricated using a metal-less graphitized contact which was produced using a high dose implantation of boron ions. The interdigitated electrode structure was produced using only graphitized diamond, patterned by ion implantation through a photoresist.Two coplanar diamond devices were fabricated, using free-standing 70 m thick undoped polycrystalline CVD diamond film grown by Element Six Ltd. Device 1 consisted of a single coplanar electrode structure, with an electrode width and interelectrode gap of 100 m. The contacts were fabricated by a conventional photolithographic lift-off process, using thermally evaporated chromium ͑50 nm͒ followed by gold ͑200 nm͒. After lift off, the sample was annealed for 10 min at 400°C in a nitrogen atmosphere to form a metal-carbide contact. Device 2 was fabricated using ion implantation with no metal contact. Prior to implantation, a 2.5 m thickness photoresist was spun onto the diamond and patterned using a conventional optical mask. The mask design was divided into four quadrants, containing four coplanar devices with a central common electrode and with electrode widths and interelectrode gaps of 5 m, 10 m, 20 m, and 50 m ͑Fig. 1͒. A broad beam ion implantation was applied to the device at room temperature using 70 keV boron ions and a dose of 2 ϫ 10 16 cm −2 . After removal of the photoresist in acetone, the device was annealed for 4 min at 700°C in a nitrogen atmosphere ...

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confidence: 97%

Performance of a diamond x-ray sensor fabricated with metal-less graphitic contacts

Sellin

Galbiati

2005

Applied Physics Letters

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“…This conclusion is in contradiction to data of Mort, Machonkin, and Okumura, who propose p-type properties of intrinsic CVD diamond based on doping experiments. 6 Given the likely variability in preparation conditions and the high defect densities, this contradiction cannot be resolved based on the presented data. Applying a forward voltage reduces the built-in potential of the illuminated contact.…”

Section: Cr/au-diamond Contact Propertiesmentioning

confidence: 72%

Electronic properties of CVD and synthetic diamond

et al. 1997

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Transport and contact properties of synthetic IIb-and intrinsic chemical vapor deposition ͑CVD͒ -diamond films are discussed. The samples have been investigated by time-of-flight and transient photoconductivity experiments using Cr/Au contacts. A hole depletion layer at the Cr/Au-IIb-diamond interface and an electron depletion layer at the Cr/Au-CVD-diamond interface is detected. The data indicate that our normally undoped CVD-diamond films are n-type semiconductors. In IIb diamond the mobilities of electrons and holes have been measured, while in CVD diamond no carrier transit can be detected due to the short Schubweg less than or equal to 1 m. Two trap levels located approximately 190 meV below the conduction band and 670 meV above the valence band are deduced. Electron spin resonance experiments demonstrate that these CVD films are highly defective, containing about 10 18 cm Ϫ3 carbon related defects (gϭ2.0029).

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“…However, disordered regions are expected to occur at grain boundaries that could explain that results. In the high temperature region the process follows a Space Charge Limited Current [6]. The exponent of non-ohmic component is near 4 indicating a existence of a band-tail with a high density of states increasing exponentially toward the conduction band where the carriers are emitted from deeper states into this bandtail.…”

Section: Resultsmentioning

confidence: 96%

Optical and electrical characterisation of iron-doped ZnO

Gaspar

Pereira

Costa

et al.

2000 International Semiconducting and Insulating Materials Conference. SIMC-XI (Cat. No.00CH37046)

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In this work the 1.7855 eV luminescence and electrical DC behaviour in polycrystalline ZnO are studied. Luminescence transient decay times of 1.4 ms and 23 ms are found at 11 K. While the first one remains constant with temperature the slower one decreases reaching a value of 5 ms at 160 K with an activation energy of' 76 meV. A fast decrease of the intensity above 30K with activation energy of 8 meV was found. Electrical DC measurements show a Space Charge Limited Current behaviour with an activation energy of 40 meV above 30K. For lower temperatures a Variable Range Hopping was found. Based on these data an excitonic model for the centre is proposed.

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Density of states distribution in diamond thin films

Cited by 41 publications

References 14 publications

Performance of a diamond x-ray sensor fabricated with metal-less graphitic contacts

Performance of a diamond x-ray sensor fabricated with metal-less graphitic contacts

Electronic properties of CVD and synthetic diamond

Optical and electrical characterisation of iron-doped ZnO

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