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NN7.6.1

Radiation Effects and Defects in Cubic Boron Nitride. A Promising Multifunctional Material for Severe Environment Conditions.

S.V. Nistor National Institute for Materials Physics, POB MG-7 Magurele-Bucuresti, RO-077125 Romania ABSTRACT Cubic boron nitride (c-BN) is a synthetic material which exhibits exceptional physicochemical properties such as: hardness, thermal conductivity, thermo-chemical stability, semiconducting properties and radiations resistance. Such outstanding properties make it a promising multifunctional material for applications in extreme conditions, as those found in the outer space environment. Its further use for such applications requires, however, a much better understanding of the lattice defects and radiation damage properties. Here we present the results of multifrequency ESR studies concerning the native and radiation induced point defects in crystalline c-BN under irradiation with high intensity 1MeV electron beams. INTRODUCTION Crystalline cubic boron nitride (c-BN) with sphalerite structure is the second hardest known material. As shown in table I, it exhibits exceptional physical and chemical properties, comparable or even superior to diamond in what concerns its semiconducting properties, lower chemical reactivity and higher thermal stability. Table I. Some typical properties of crystalline c-BN in comparison with those of diamond Property Hardness Refractive index (at 589.3nm) Band gap (indirect) (eV) Resistivity (Ω.cm) Thermal stability (in O2) Thermal conductivity (Wcm-1K-1) Cleavage Structure – lattice parameter

c-BN < 10 (next after diamond) 2.117 6.25 Intrinsic: 1010 p (Be): 102 -104 n (Si,S,O): 103-107 Up to 1600K 13 {110} Cubic (blende) a = 0.3615nm

Diamond 10 2.417 5.47 Type I, IIa >1018 Type IIb: >103-105 Under debate Up to 900K 20 {111} Cubic (simple) a = 0.3567nm

The energy band-gap (indirect) of cubic boron nitride, of ~ 6.3 eV at room temperature [3], is the highest among all covalent-bonded materials known so far. Such wide band-gap is suitable for ultraviolet (UV) detectors and UV light emitting diodes operable at wavelengths in the deep UV regime Moreover, both p-n junctions and UV-light emitting diodes could be operated at temperatures as high as 900K, without significant parameters changes [1]. Recently it has been

NN7.6.2

found out [2] that c-BN is highly resistant to radiation damage as well. The use of c-BN as an advanced material with superior properties for applications such as: laser active and optical upconversion material [3], cold cathodes [4], or bio-sensors [5], had been also shown to be feasible. All these investigations strongly suggest that c-BN is a very promising multifunctional material for semiconductor and optical devices in the extreme conditions characteristic for the outer space environment. Further development of c-BN based materials for such advanced applications requires, however, understanding the properties of natural and radiation induced lattice (atomic) defects, their structure and associated energy states that are essen