Electron-hole drops in synthetic diamond

(I)n this paper we give the first report of a high-density phase of condens ed electron-hole drops in diamond. Synthetic crystals grown by the high pre ssure-high temperature technique were optically highly excited by laser pul ses with photon energies above the band-gap of diamond. At temperatures bel ow approximate to 170 K we observe novel broad luminescence bands, in addit ion to the well-known free exciton spectra. with characteristic features id entifying them as originating from electron-hole drops. Fits to the photolu minescence spectra yield an electron-hole density within the drops of n(0)= 9.6 x 10(19) cm(-3), a reduced band-gap of E-g'=5.224 eV (instead of E-g=5. 49 eV) due to the attractive interaction of the particles in the condensed phase, and a work function of phi = 52 meV with respect to the free exciton threshold E-gx. (C) 2000 Elsevier Science S.A. All rights reserved.