Single Crystal CVD Diamond Growth for Detection Device Fabrication
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1039-P10-03
Single Crystal CVD Diamond Growth for Detection Device Fabrication Nicolas Tranchant, Dominique Tromson, Philippe Bergonzo, and Milos Nesladek CEA\LIST Saclay, DRT\LIST\SSTM\LTD, Bat 451, Pce 74, Gif Sur Yvette, 91191, France, Metropolitan Abstract Single crystal (SC) CVD diamond is known to exhibit superior electronic properties compared to polycrystalline diamond for detection applications. In our study, samples were grown using the Chemical Vapor Deposition (CVD) technique in an ASTEX AX 5400 reactor, at various microwave powers and keeping all other parameters constant. The crystalline quality and purity of samples were investigated using Raman spectroscopy and cathodo-luminescence measurements. The diamonds layers were chemically cleaned and oxidized, prior to their fabrication as ionization chambers using Ni and Au contacts for rectifying properties. Device electronic and detection properties were then characterized: Leakage currents were probed from I(V) measurements and contact properties were tested with 60Co source at various dose rates. Time of Flight (TOF) and Charge Collection Efficiency (CCE) measurements were evaluated with 241Am alpha particles irradiation, which enabled the measurements of mobility, carrier diffusion length and lifetime as a function of growth parameters. These measurements demonstrate the importance of growth condition optimization on the detection quality of these samples. 1. Introduction Due to superior electronic properties of diamond such as high carrier mobilities (higher than 1000 cm2/Vs) which are required for detection applications in radiotherapy, single crystalline (SC) diamonds have been grown homo-epitaxially on Ib HPHT substrates. A microwave plasma enhanced chemical vapor deposition (MPCVD) technique was used to reduce defect incorporation into these samples during growth. In order to reduce the number of defects and to obtain a surface as smooth as possible, we have applied oxygen plasma pre-treatment to the HPHT substrates [1]. The aim of this study is to correlate the growth conditions, the crystalline quality of the samples and their charge transport properties. Two growth parameters have been investigated in particular, namely the methane concentration and the plasma density. To vary the plasma density two ways can be applied, either changing the pressure applied or modifying the microwave power applied. By convenience, we choose to change the applied microwave power. 2. Experimental details Samples were grown in an AX5400 ASTEX reactor, with a base pressure of 10-7mbar, on commercial Ib HPHT single crystal substrates (100) oriented surfaces. To study the influence of methane, we operated at a microwave power of 500 W and at a pressure of 240 mbar. The methane concentration has been varied from 1 to 10 % while all other parameters were kept
constant. To study the influence of microwave power, we operated at a constant pressure of 240 mbar keeping the methane concentration constant at 2 %. Indeed, using this low methane admixture allowed to investig
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