Detectors sensitive to ionizing radiations were assembled from high-purity single-crystal diamond plates with Ti/Au
injecting contacts. Spectrally resolved photoconductivity measurements in the range 2-6 eV were used to infer the defect
density in the diamond bulk material using silver contacts. The electrical behavior of annealed Ti/Au contacts was
analyzed in the dark through current-voltage measurements in the range ±500V (10<sup>4</sup> V/cm). Although contacts appear to
be ohmic in the dark, two different transport regimes were found under x-ray irradiation as a function of the applied bias
voltage. Recombinative regime at low bias and space charge limited injection regime at high bias were evidenced. The
analysis of the photocurrent's module and phase under x-ray modulated irradiation allowed us to highlight
photoconductive gain phenomena mitigated by a Poole-Frenkel field-assisted detrapping process. Through the analysis
of device's impedance under irradiation, a lumped-elements electrical circuit is proposed to explain the detector's
Optically triggered surface channel MESFETs were fabricated on commercial polycrystalline diamond to be tested as
fast UV activated switches. Devices with an opaque-gate and asymmetric structure were designed in order to improve
charges photogeneration within gate-drain region. The sensitivity to UV light was demonstrated by using both modulated
over gap radiation and laser pulses at 193 nm, well over the diamond band gap. Linearity with the power light was
demonstrated as well as the parabolic dependence of the photogenerated current on the gate-source voltage when the
transistor is in saturation. The transient response to 193 nm laser pulses in the nanosecond regime shows as the
photogeneration process and charges collection to the drain contact are completed in a time scale of few nanoseconds.
Laser beam profiling technology in the UV spectrum of light is evolving with the increase of excimer lasers and lamps
applications, that span from lithography for VLSI circuits to eye surgery. The development of a beam-profiler, able to
capture the excimer laser single pulse and process the acquired pixel current signals in the time period between each
pulse, is mandatory for such applications. 1D and 2D array detectors have been realized on polycrystalline CVD
diamond specimens. The fast diamond photoresponse, in the ns time regime, suggests the suitability of such devices for
fine tuning feedback of high-power pulsed-laser cavities, whereas solar-blindness guarantees high performance in UV
beam diagnostics, also under high intensity background illumination. Offering unique properties in terms of thermal
conductivity and visible-light transparency, diamond represents one of the most suitable candidate for the detection of
high-power UV laser emission. The relatively high resistivity of diamond in the dark has allowed the fabrication of
photoconductive vertical pixel-detectors. A semitransparent light-receiving back-side contact has been used for detector
biasing. Each pixel signal has been conditioned by a multi-channel read-out electronics made up of a high-sensitive
integrator and a Σ-Δ A/D converter. The 500 μs conversion time has allowed a data acquisition rate up to 2 kSPS
(Sample Per Second).
Polycrystalline diamond detector prototypes suitable for x-ray spectroscopy were realized and tested. Thick diamond specimens, mechanically polished to reduce the surface roughness, were selected for prototypes development. Noble metal contacts were deposited on both faces, whereas multistrip structures were defined by photolithography on the growth face only with the aim of reducing the coupling capacitances and to allow characterization tests either in
planar or sandwich configuration. Leakage currents as low as 20 pA at 500 V were measured on a 270μm thick device. The x-ray sensitivity was tested monitoring the photocurrent as a function of the applied voltage under continuous 8.05 keV Cu Kα irradiation. Studies in pulsed mode were also performed by using a commercial miniature x-ray source. Pulse height distributions were carried out with a system composed of a charge-sensitive preamplifier and a digital pulse processor multi-channel analyzer. Analysis was carried out around Ta Lα and Cu Kα characteristic lines. Realized prototypes were able to resolve such two characteristic lines only 90 eV apart. Energy resolutions better than 3% have been evaluated for one of the prototype at 8.14 keV. Such features address very good energy resolving capabilities and the suitability of polished polycrystalline diamond in x-ray spectroscopy.
The electrical activity of nitrogen related defects are investigated in ultra-nanocrystalline diamond (UNCD) films
achieved using different N<sub>2</sub>% in the gas phase by transient photocurrent technique at λ = 193 nm, and by steady state
photocurrent measurements in the photon energy range 1-6 eV.
In undoped UNCD films, spectrally resolved photocurrent measurements reveal a threshold at about 1 eV, related to
the absorption of non diamond carbon phases, followed by a monotonic increase by more than one order of
magnitude up to about the diamond energy gap, where a steep rise occurs due to band to band transitions. In nitrogen
doped UNCD films a clear onset of the spectral photocurrent signal is hardly detectable, although an apparent shift
towards higher energies is evidenced, in agreement with a possible nitrogen induced Fermi level shift upward in the
band gap. The main N-related feature of the spectra is however a sharp peak at about 4 eV, which is also observed in
polycrystalline diamond films grown in a nitrogen rich gas mixture, particularly close to the boundary of the
On the other hand, photocurrent pulse shape analysis gives carrier lifetime values in the 6-10 ns range, almost
independent of nitrogen content. Instead, N-related defects appear mainly responsible for trapping processes, which
slow down carrier transport and give rise to long transit times.
Such results are discussed in terms of photoionization of N-related defects formed in the non diamond carbon phase.
The feasibility of diamond position sensitive detectors for deep UV light monitoring is reported. Based on voltage-division
principle, a very simple one-dimensional photosensitive structures have been developed exploiting the strong
variation of polycrystalline diamond conductivity under UV-light irradiation and dark conditions. Lumped and finite
elements analysis have been used to compare the theoretical expectations with the experimental results obtained under
excimer laser illumination. A complete characterization of such a 1D position sensitive device has been performed in
terms of: the beam intensity insensitivity (over three orders of magnitude); the output signal dependence on the beam
width; and the contact structure and its resistance influence on the device performances.
The photo-response of AlGaN based UV detectors to a 193 nm excimer laser radiation is presented. Two devices have
been tested and compared, a metal-semiconductor-metal (MSM) planar structure and a Schottky diode. These sensors
have already shown good performances in the 240-280 nm region under CW illumination and have been used for the
realization of 2D and linear arrays. Here the capability of these devices to detect the emission of a nanosecond pulsed
excimer laser is proven and the decay time and dependency on the beam's density of energy evaluated. The measured
transient response of the MSM device closely follows the nanosecond laser pulses, with a decay time shorter than 3 ns.
Conversely, the Schottky diodes showed a slower rise and decay kinetics principally limited by the coupling with the
junction capacitance. The decay curve of such a device has been analyzed on the basis of two decay mechanisms: the
second exponential decay has been found to be in the order of 40 ns. This slow kinetic has been attributed to the presence
of trap states localized at a distance from the conduction or valence band larger then the thermal energy of the carriers.
Both the realized devices do follow the Rose's law with a linear response at the lower beam fluxes (density of energy
4×10<sup>-5</sup> - 0.2 mJ/mm<sup>2</sup>) and a transition to a sub-linear regime for higher fluxes.