INCORPORATION OF LITHIUM IN SINGLE-CRYSTAL DIAMOND - DIFFUSION PROFILES AND OPTICAL AND ELECTRICAL-PROPERTIES

Doping of diamond by in-diffusion of lithium in natural type Ia and II a single crystal diamond plates has been investigated. The lithium inc orporation was realized by direct in-diffusion from a Li2O source at t emperatures between 400 and 650 degrees C. Using secondary ion mass sp ectroscopy (SIMS) depth profiling, high concentrations of lithium, up to a level of 8.0 x 10(21) cm(-3) and gradually decreasing to 1.0 x 10 (19) cm(-3) at a depth of 0.5 mu m below the surface, were measured. F rom these profiles the diffusion constant of lithium in diamond was de termined to be D-Li(T)=2 x 10(-10) exp (-0.9 eV/kT) cm(2) s(-1). The a ctivation energy for diffusion of 0.9+/-0.3 eV is in agreement with th e theoretical Literature value of 0.85 eV. Cathodoluminescence spectro scopy showed that the blue band-A luminescence, which is characteristi c for natural type IIa diamond, is largely quenched by the presence of lithium. A shift of the maximum luminescence intensity towards higher energy values has been found. From photothermal deflection spectrosco py and optical transmission measurements no new optically active defec t is observed after lithium in-diffusion. However, these measurements indicated the occurrence of a large concentration of light scattering centres, the size of which is IO nm or less. This suggests that lithiu m is clustered in the crystal volume just below the specimen surface a nd therefore is not electrically active. (C) 1997 Elsevier Science S.A .