GEAS AS A NOVEL ARSENIC DIMER SOURCE FOR N-TYPE DOPING OF GE GROWN BYMOLECULAR-BEAM EPITAXY

GeAs is successfully applied as a new arsenic dimer source for efficie nt n-type doping of Ge grown by molecular beam epitaxy. The arsenic fl uxes emanating from GeAs Knudsen cells are not composed of arsenic tet ramers, but only of arsenic dimers. High electron concentrations of up to 1.1X10(20) cm-1 are achieved with GeAs, which is much larger than any ever obtained in antimony-doped Ge. The electron concentration in the arsenic-doped Ge films depends on the GeAs cell temperature with a n activation energy of 2.5 eV, which coincides with that of the arseni c dimer beam flux generated from GeAs. Moreover, it is found that the electron and arsenic concentrations in the arsenic-doped Ge layer are identical. These results indicate that arsenic atoms are incorporated into Ge from the arsenic dimer beam, and that a very high electrical a ctivation of the incorporated arsenic atoms is obtained.