Development of single‐crystal CVD‐diamond detectors for spectroscopy and timing

Abstract

Charge‐transport parameters measured for several single‐crystal CVD‐diamond films are discussed as well as the consequences for the energy‐ and the time resolution of charged‐particle detectors made of these samples. Applying a transient‐current technique, where 241Am α‐particles are used for e–h pair creation, low‐field electron mobility values varying in the range 1300 < µ 0–e [cm2/Vs] < 3100 are obtained, and a common saturation velocity around v sat–e ≈ 1.9 × 107 [cm/s]. Hole data show impressive uniformity with µ 0–h ≈ 2330 [cm2/Vs] and v sat–h ≈ 1.4 × 107 [cm/s]. At detector operation bias (0.3 V/μm < E D < 3 V/μm) the holes drift systematically faster than the electrons. The lifetime of the charge carriers in best samples amounts to τ h ≈ 1 µs for holes and to τ e ∼ 320 ns for electrons. Comparable to the energy resolution of commercial silicon detectors, a ΔE = 17 keV (FWHM) is measured for 5.5 MeV α‐particles and ΔE /E ∼ 1% for heavy ions. Tests of single‐ and polycrystalline detectors with relativistic 27Al ions of 2 AGeV reveal the same intrinsic time resolution of σ (Δt) = 28 ps indicating limitations due to electronic noise. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ion spectroscopy — A diamond characterization tool

“…Furthermore, the theory [2][3][4] refers usually to pindiode structures, where single-carrier drift is assumed. If the case of dual-carrier drift is treated [3], significantly lower mobility of minority carriers is implemented, which is not correct for diamond [10]. It is also not clear if the variation of Q Bi at constant Q G , as performed in the present study, is compatible to the variation of the charge injection Q G at constant bias.…”

“…Aiming for precise measurements of the so far missing stopping power of diamond and the corresponding energy-loss of heavy charged particles in it, an electrical characterization method for highquality materials is found, which completes the measurements performed with short-range ionizing sources (e.g., α-particles [8][9][10], UV photons [11]) or with minimum ionizing particles (MIP) [12]). Even if MIPs show similarities to the probes proposed in this article, they generate in contrast weak charge signals and spectra revealing the characteristic asymmetric shape of a Landau distribution [13].…”

“…The RC time constant of the system was in this case as short as 45 ps at 50 Ω impedance, i.e. RC b t Tr [10]. The bias resistor was chosen to 10 kΩ, in order to ensure constant voltage on the electrodes at all times, and thus to perform the measurements in the so called 'current mode'.…”

“…At the current status of the simulations, the following input parameters are implemented: no recombination (infinite carrier lifetime), a diamond bulk almost without impurities (number of acceptors N A = 10 3 ), intrinsic carrier concentration N intr =10 5 /cm 3 , and a fielddependent mobility. The initial transport parameters are taken from α-measurements reported in [10]. Corresponding to the generated charge Q G = 19.22 pC, a total number of 1.2 ⁎ 10 8 e is injected homogeneously in ten points along the beam axis of a diamond material of relative permittivity ɛ r = 5.7.…”

“…In the data discussion, the experimental results will be compared to values calculated according to LS [1], which has overruled the Bethe-Bloch theory in the relativistic ion range. In the configuration of an ion spectroscopy detector, a sample is biased with U Bias and read out by an integrator circuit of a decay time constant RC N t Tr , the latter being the thickness dependent transition time of the collected charge which is for intrinsic mono-crystalline CVD diamond in the order of a few nanoseconds [10]. The separated electrons and holes drift to both electrodes (dual-carrier current), while creating an 'ion-induced' current signal.…”