Experimental determination of electron and hole mean drift distance: Application to chemical vapor deposition diamond

Abstract

A simple technique for measuring the electron and hole mean drift distance in chemical vapor deposition polycrystalline diamond in the as-grown and in the so-called pumped state obtained by 90 Sr ␤-particle irradiation is presented. To this purpose, the efficiency of a diamond-based particle detector was measured using a 5.5-MeV 241 Am ␣-particle source. In particular, two different experimental setups were specifically designed and realized in order to perform a systematic study of the device efficiency as a function of the ␣-particle penetration depth, both in the positive and negative bias polarization. In the first setup, air is used as an absorbing layer in order to change the energy of the impinging ␣ particles, while in the second one, the measurements were performed in vacuum and the incidence angle was varied in the 0°-80°range. The advantages of the latter setup are evidenced. The theoretical formula for the mean drift distances of carriers is derived using a properly modified Hecht model, and fitted to the data, allowing a separate evaluation of the charge collection distances of each carrier type ( e ϭ e e E and h ϭ h h E). The obtained results unambiguously show that the pumping process is much more effective on hole conduction, h being much greater than e in the pumped state. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1586475͔Chemical vapor deposition ͑CVD͒ diamond has been shown to be a suitable material for a great number of technological applications, such as particle and UV radiation detectors, 1-4 and even more so if it is driven in the so-called pumped state by ionizing irradiation, which is known to drastically improve the transport properties of synthetic diamond. 5,6 However, despite the large diffusion of the procedure, few authors have carefully studied the physical grounds of the pumping process in order to discriminate its effect on electron and hole propagation in the detection process, [7][8][9][10][11][12] so that very little is known to date about the contribution of each carrier type to the transport mechanism in the as-grown and pumped states.The aim of the present work is to carefully separate and evaluate the charge collection distance of electrons and holes in polycrystalline CVD diamond, both in the as-grown and pumped states, thus giving a better insight on the transport properties of such material. To this purpose, a 130-m-thick film was grown in our labs by microwave plasma chemical vapor deposition and a particle detector was realized and tested with a 241 Am ␣-particle source, as described elsewhere. 13 The mean drift distance of each carrier type can be separately obtained by systematically studying the efficiency of the device as a function of the incident particle penetration depth G, and by analyzing the experimental curves in the framework of a properly modified Hecht model. Indeed, the contribution of one type of carrier ͑de-pending on bias polarity͒ gradually decreases as the penetration depth is reduced.A crucial point of this work was the design and r...

Experimental determination of the PTW 60019 microDiamond dosimeter active area and volume

“…In particular, the α-particle energy detected by such diamond detectors was studied as a function of the incidence angle between the beam direction and the normal to the detector surface. 23,25 The penetration depth of α-particle in diamond is 13.54 µm, which is definitively higher than the nominal thickness of an MD, which is 1 µm. A fraction of the energy of the impinging α-particles is thus collected by the diamond detector in normal incidence irradiation conditions.…”