Diamond has recently been shown to be a viable material for detectors in experiments at the next generation of particle accelerators. This contribution surveys the properties of diamond which give it advantages, the results achieved to date, the remaining unresolved issues, and the possible applications for diamond detectors in the future

Dulinski, W

Gan, K K

Han, S

Hassard, J

Howard, A

Kagan, H

Kanda, S

Kania, D R

Kass, R

Kim, S K

Malchow, R L

Nygård, E

Pan, L S

Roe, S

Schnetzer, S R

Stone, R

Straver, J

Sugimoto, Y

Tesarek, R J

Thomson, G B

Trischuk, W

Turchetta, R

Wagner, R

Weilhammer, Peter

White, C

Zhao, S

CERN Document Server

EUROPEAN ORGANISATION FOR NUCLEAR RESEARCHCERN PPE/94-222December 2, 1994Diamond Detectors for Future Particle Physics ExperimentsyW. Dulinskia, K.K. Ganb, S. Hanc, J. Hassardd, A. Howardd, H. Kaganb, S. Kandae, D. Kaniaf,R. Kassb, S.K. Kimg, R. Malchowb, E. Nygardh, L.S. Panc, S. Roei, J. Straveri, S. Schnetzerj,R. Stonej, Y. Sugimotok, R. Tesarekj, W. Trischuki, G.B. Thomsonj, R. Turchettaa, R. Wagnerc,P. Weilhammeri, C. Whiteb, S. ZhaobaLEPSI, CRN Strasbourg 67037, FrancebDepartment of Physics, The Ohio State University, Columbus, OH 43210, USAcResearch Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USAdBlackett Laboratory, Imperial College, London, SW7 2BZ, UKeDepartment of Physics, University of Hawaii, Honolulu, HI 96822, USAfLaser Division, Lawrence Livermore National Laboratory, Livermore, CA 94550, USAgDepartment of Physics, Seoul National University, Seoul, Korea 151-742hUniversity of Oslo, 0316 Oslo 3, NorwayiCERN,CH-1211 Geneva, SwitzerlandjDepartment of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854, USAkKEK, Tsukuba-shi, Ibaraki-ken, Japan 305AbstractDiamond has recently been shown to be a viable material for detectors in experiments at the nextgeneration of particle accelerators. This contribution surveys the properties of diamond whichgive it advantages, the results achieved to date, the remaining unresolved issues, and the possibleapplications for diamond detectors in the future.1. IntroductionThe inherent properties of diamond make it an idealmaterial for close-in tracking detectors especially inthe high rate, high radiation environments of futurecolliders such as the LHC. We have constructedy Contibution to the proceedings of ICHEP94, Glasgowand tested micro-strip detectors using high qualityChemical Vapour Deposited (CVD) diamond. Whilethis is an important rst step a number of issuesremain: establishing the radiation hardness of thematerial to be sucient to survive in regions of highenergy physics detectors where silicon cannot, andmaximisation of the charge observed when a minimum2Property D Si Ga AsBand Gap [eV] 5.5 1.12 1.43Breakdown eld [V/cm] 10731054105Resistivity [-cm] > 10112.3105108Intrinsic Carrier Density [cm 3] < 1031.51010 108Electron Mobility [cm2V 1s 1] 1800 1350 8500Hole Mobility [cm2V 1s 1] 1200 480 400Saturation Velocity [km/s] 220 82 80Mass Density [gm cm 3] 3.5 2.33 5.32Atomic Charge 6 14 31, 33Dielectric Constant 5.7 11.9 13.1Thermal Exp. Coef. [10 6/K] 0.8 2.6 6.9Thermal Cond. [W cm 1K 1] 10-20 1.5 0.45Cohesive Energy [eV/atom] 7.37 4.63Energy to create e-h pair [eV] 13 3.6 4.2Radiation Length [cm] 12.0 9.4 2.3Sp. Ionisation Loss [MeV/cm] 4.69 3.21 5.6Ave e-h pairs/100 m [e] 3600 8900 13000Ave e-h pairs/0.1% X0[e] 4500 8400 3000Table 1. The physical properties of diamond, silicon andgallium arsenide at 293K.ionising particle traverses the material. Work on theradiation hardness of the material is underway witha number of irradiations complete and others in theplanning stages. Two ways of increasing the detectedcharged particle signal are investigated by increasingthe intrinsic charge collection distance of the materialand by optimising the contacts on the surface of thedetector.Diamond oers unique possibilities for particledetector applications [1],[2]. This is primarilydue to its very tightly bound lattice which resultsin extraordinary electrical, mechanical and thermalproperties. Its atomic structure results in very fewfree charge carriers and hence very low leakage currentsin the presence of an external electric eld. Its highcarrier mobility also suggests that as a simple ionisationdetector intrinsic diamond may be one of the bestchoices. In Table 1 we list some of the physicalparameters of diamond along with silicon and galliumarsenide for comparison.One of the few drawbacks seen from Table 1 is thatthe number of electron-hole pairs created by a minimumionising particle in diamond is smaller than either insilicon or gallium arsenide. This stems mainly fromthe larger band gap in diamond and hence the largerenergy necessary to create a pair. However in the limitthat the signal collection distance, the average distancean electron and hole separate under the inuence ofan applied electric eld [3], can be made comparableto the thickness of the material the signal in diamondcan be made half as big as that in silicon and thenmany of the other advantages of diamond may becomereal assets. As a result of R&D work undertakenfor detectors being designed for the SSC and LHCthe charge collection distance in CVD diamond hasincreased from a fraction of a micron ve years ago,to almost 75 microns today. This represents chargecollection distances that are almost 3 times larger thanthose found in natural single-crystal diamonds. Oneof the main reasons for such large advances has beenin learning to grow CVD diamond with low defectdensities and large crystallites.In developing a detector with this material thesurface preparation is also an issue. Good ohmiccontact between the surface electrodes and the diamondis necessary to remove charge as it is created by thetraversal of charged particles. Otherwise this chargebuilds up at the surface and results in a polarisationeld which osets the applied bias. The studies weare undertaking aim to optimise this aspect of detectorfabrication as well.To make a viable high energy physics detector oneway to accomodate a low signal is to lower the noisein the readout electronics. Several of the physicalproperties of diamond are assets here as well. The verylow leakage currents which result from the material'shigh resistivity imply reduced shot noise. The dielectricconstant of diamond is half that of silicon thus all loadcapacities in a comparably laid-out diamond detectorwill be half those found in a silicon detector. Weaim to develop detectors which have signal to noiseratios of at least 15:1 to allow pattern recognition witha diamond based tracker as well as to facilitate theassociation of hits in a diamond detector to tracksreconstructed elsewhere. In order to reach this goalit will be necessary to increase the diamond signal byabout a factor of four over that available today and alsoto reduce the noise in LHC type ampliers by a factorof two or more.It is possible to study, in many ways, the materialproduced when CVD diamond is grown. Some of thesecan be related to the charge collection distance in thematerial. Cathodoluminescence, photoluminescenceand absorption spectroscopy can reveal impurities anddefects in the material. Graphitisation can be studiedwith Raman spectroscopy and SEM/TEM techniques.A survey of these methods can be found in [4].2. Results in Particle TestbeamsEarly on in the SSC research programme it wasdecided to demonstrate diamond's potential in a simplecalorimeter [5]. The calorimeter was designed to allowa direct comparison with silicon active layers. Thesuccess of this detector gave us condence to move onto the application of diamond in a tracking detector.It is a measure of diamond's versatility that someof the diamond material used in the calorimeterwas recycled into the detector material for the rst3 020406080100-150 -100 -50 0 50 100 150Figure 1. The experimental position resolution of the diamonddetector, compared to the predicted charged particle impactpoint based on the silicon telescope information. The t of asingle Gaussian gives a sigma of 26 m.tracker [6]. In this work a silicon telescope [7] consistingof 4 reference point measurements in the x and yprojections allowed us to pinpoint the position of 50GeV pions with 3 m precision on the surface of thediamond detector.The diamond detectors used in this work wereplanar 880:3mm3with 50 mwide strips on 100 mcentres. A bias voltage was placed across the smallestdimension of the detector to push holes towards thereadout strips which were arrayed on the surface. Thedetector strips were DC coupled to individual Viking [8]channels. Data were taken with normally incidentparticles, at a variety of bias voltages and with a 2s shaping time. Our analysis showed that at a biasvoltage of 195V we obtained a S/N of 6:2 0:2 and aposition resolution of 25  1 m. The eciency of thedetector was greater than 86 %; no correction for deadchannels was made.From these data we infer an average signal size of1400180 electrons consistent with the charged particlesignal expected from tests of the diamond's collectiondistance measured before construction of the tracker.While this signal size is not adequate for an LHCdetector, where the shaping times will have to be about50 times smaller and hence the noise can be expected tobe at least 7 times larger, it does provide rst evidencethat CVD diamond can be used as a charged particletracker.00.20.40.60.811.21.41.61.8210-410-310-210-11 10 102Figure 2. Exposure of CVD diamonds to90Sr and60Cophotons. The rst four points were Sr irradiations while theothers were done with Co. The gain plotted is the chargecollection distance observed after a given dose relative to theunirradiated collection distance.3. Radiation damage in Diamond DetectorsThere are two primary manifestations of radiationdamage in solid state detectors. One is an increasein leakage current and the other is a decrease is signalpulse height. The tightly bound lattice structure ofdiamond suggests that it will be insensitive to largedoses of radiation. Previous studies (neutrons [9],[10]and 1.5 MeV electrons [11]) have shown that naturaldiamond is very resistant to both types of damage.During the last few years we have undertakenseveral studies of radiation damage to CVD diamonddetectors. In each study the collection distance wasmeasured before and after the irradiation. In the rststudy we used photons (1.2 and 1.3 MeV) from a60Cosource. As can be seen from Figure 2 up to doses of10 MRad there is no evidence of degradation of theelectronic properties in CVD diamond. As can alsobe seen from this gure, at low doses the collectiondistance improves with accumulated dose. This curiouseect is generally believed to be due to a passivation ofcharged traps.In addition to the photon irradiation describedabove we have recently completed irradiations with 5MeV alpha particles (no change in the gain up to 1013alpha's/cm2), 300 MeV pions (under analysis), and500 MeV protons (under analysis). Preliminary resultsseem to conrm the radiation hardness expected. In thenear future we will complete our irradiation programwith studies of neutrons and electrons.44. Future Directions for Diamond Detectorsin Particle PhysicsIn the coming year it should be possible, by activelyworking with manufacturers, to obtain high qualityCVD diamonds with collection distances of 200 m. Atthis level, diamond-based detectors would work at theLHC and at HERA-B. Other detector congurations(e.g. pixels) could also be considered.We note in closing that the use of diamond is notrestricted to particle detection. Diamond is alreadyused extensively in thermal management and it mayalso play a role in mechanical support.5. References[1] M. Franklin et al., Nucl. Instr. and Meth. A315 (1992) 39.[2] CERN/DRDC 94-21, DRDC-P56, RD42 Proposal.[3] S. Zhao, Ph.D. Thesis, The Ohio State University (1994).[4] J. Field, (ed) The Properties of Natural and SyntheticDiamond, (Academic press: London), 1992.[5] R.J. Tesarek et al., Nucl. Instr. and Meth. A349 (1994) 96.[6] F. Borchelt et al., CERN PPE/94-113, accepted forpublication in Nucl. Inst. and Meth. A.[7] C. Colledani et al., \A High Resolution Beam Telescope",CRN-LEPSI internal note.[8] E. Nygard et al., Nucl. Inst. and Meth. A301 (1991) 506.[9] S.F. Kozlov et al., IEEE Trans. Nucl. Sci. NS-22 (1975)160.[10] E.R. Vance et al., J. Phys. D 5 (1972) L40.[11] M. Geis, private communication.

Diamond detectors for future particle physics experiments

Diamond detectors for future particle physics experiments

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