Fast Diamond Photoconductors
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FAST DIAMOND PHOTOCONDUCTORS C. RUBBELYNCK* T. POCHET*, B. BRULLOT*, R. GALLI*, *LETI (CEA-Technologies Avanc~es), DEIN/SPE, Centre d'Etudes Nuclaires de Saclay, 91191 Gif-sur-Yvette Cedex, France **Centre d'Etudes Nucl~aires, DAM/CEM, B.P. 12, 91680 Bruy~res-le-Chatel, France
ABSTRACT Preliminary results on the response of type Ib and Ila diamond photodetectors to fast laser pulse exposures at 265 and 530 nm are presented. The influence of the applied bias, the laser wavelengths and the light intensity on the detector sensitivity is studied. Also, recent measurements with 1.25 MeV gamma ray pulses are reported. 1- INTRODUCTION Over the last few years, picosecond photoconductors have been subject to a growing interest [1-5] for a wide range of applications. Such devices using either high resistivity neutron irradiated semi-insulating GaAs or InP:Fe are currently designed in our laboratory for the analysis of fast gamma ray pulses over a very wide dynamic range [6]. Analysis of very soft Xray subnanosecond pulses in the keV domain require a photoconductor having a lower atomic number that GaAs in order to enhance bulk radiation induced conductivity. Diamond seems to be the most promising candidate because of its low atomic number, its very high dark resistivity and its high carrier mobility. Moreover its resistance to radiation damage and the capability of high temperature operation render this crystal very attractive [7-11]. In this paper we present the responses of type lb and Ila diamond photoconductors to laser pulses at 265 nm and 530 nm. The dependence of the sensitivity on the applied bias, the laser wavelengths and the energy of the laser pulses is studied. In the first section, devices are presented and the quality of the electric contacts is determined by current-voltage measurements. In the second section the experimental set-up is described and results including the sensitivity of the different photoconductors under various types of illumination are reported. 2- PREPARATION AND CHARACTERIZATION OF THE DEVICES ohmic contacts on diamond Several techniques have been developped to yroduce 3 [8,12,13]. Both types Ib and Ila samples are 2x2xI mmr in size. Contacts are deposited on the two opposite larger faces. Various metallic contacts investigated include carbon paint, Ti/Pt/Au and Mo. The ohmicity of the contacts is evaluated by studying the I(V) behaviour of the samples in both polarities. show a linear behaviour up I(V) characteristics on a Ib diamond with Ti/Pt/Au contacts 4 to 1000 Volts, corresponding to an electric field of 10 V/cm (see Figure 1). Also, photoconductivity measurements have been carried out in order to evaluate the diamond optical absorption as a function of the light wavelength. A 2.8 eV transition in the Ib type diamond and a 5.44 eV transition in the Ila diamond have been observed.
Mat. Res. Soc. Symp. Proc. Vol. 302. ©1993 Materials Research Society
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Figure 1.I(V) characteristics for the lb diamond with Ti/Pt/Au
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