PARAMETERS OF CLEAVED ANNEALED AND OXYGEN AND HYDROGEN COVERED SURFACES OF GE AND SI BY PARTIAL SPLIT TECHNIQUE

When splits greater than a critical size (1 mm) are closed in Ge and Si, portions of the sides near the top do not recontact and are effectively separate surfaces. Such assemblies have been prepared in ultra high vacuum and exposed to O2, H2 and air. The effects of adsorption on the surface barrier heights have been determined by a new technique, using analysis of photovoltage measurements. For 2.0 ohm cm n-type Ge, the surface barrier decreases by approx. 0.03 eV on annealing the cleaved surfaces to above the surface transition zone (150°C, 20-30 min). Upon oxygen adsorption, the cleaved surface barrier increases initially by 0.004 eV and then decreases steadily. The initial increase, for annealed Ge, is 0.02 eV. For cleaved Si, heavy oxygen exposures (up to 1 Torr min) reduce the barrier by approx. 0.03 eV. No effect of molecular hydrogen on Ge was found, but in the case of Si an effect was found, corresponding to a barrier height decrease of approx. 0.01 eV caused by the hydrogen. Exposure to air caused large effects and, in the case of p-type Ge, a reversal in the sign of the surface barrier. The accumulated evidence indicates four separate modes of recontact of surfaces in small controlled partial splits. © 1969.