LITHIUM DOPING AND PHOTOEMISSION OF DIAMOND THIN-FILMS

Diamond films have been in-diffused with lithium in an effort to produce n-type diamond by interstitial doping. Although lithium incorporation was established, only small changes in electrical conductivity and no thermionic emission from donor levels, which should lie only a few tenths of an electron volt below the vacuum level, were observed. To account for these observations, studies of the spectral dependence of external photoemission of lithium-doped and undoped films were undertaken. These indicate that the lithium donors are compensated by high densities of acceptor states distributed over several electron volts. This first, direct observation of band-gap states in diamond films accounts for a number of reported properties including their relatively high electrical conductivity and small field effect.