Vapor-Deposited Single-Crystal Germanium

Germanium layers have been formed on single-crystal Ge substrates by the thermal decomposition of GeI2. The single-crystal nature of the layers has been established by x-ray and electron diffraction examination and by electrical measurements. The deposition process is described briefly. The crystal growth rate varies with crystal direction, and under certain conditions Ge whiskers appear. The layers as deposited are generally n type; ρ ranges from 1 to 5 ohm-cm and μH from 1200 to 2700 cm2/v-sec at room temperature. A donor level is found approximately 0.2 ev below the conduction band, with a concentration of active centers of about 1016/cm3. Heat treatment at 550°C gradually converts the layers to p type, for which ρ is 10 to 40 ohm-cm and μH 1500 to 2400 cm2/v-sec at room temperature; an acceptor level is found at about 0.05 ev above the valence band, with a density of active centers of 1014 to 1015/cm3. The layers can be doped intentionally to produce either conductivity type, permitting fabrication of junction devices. Although iodine and other impurity atoms are considered, it is concluded that interstitial Ge atoms and lattice vacancies, occurring in unequal numbers at the time of deposition, are the most likely source of the donor and acceptor levels, respectively, and of the observed heat treatment properties.