Positron-induced Auger-electron study of the Ge(100) surface: Positron thermal desorption and surface condition

Positron-annihilation-induced Auger-electron spectroscopy (PAES) was used to study the effects of oxygen, residual gases, and temperature on a Ge(100) surface. Three low-energy Auger peaks were detected at 50, 90, and 100–150 eV, attributed to ${\mathit{M}}_{2,3}$ ${\mathit{M}}_4$ ${\mathit{M}}_4$, ${\mathit{M}}_{2,3}$ ${\mathit{M}}_4$V, and ${\mathit{M}}_1$ ${\mathit{M}}_4$ ${\mathit{M}}_4$ Auger transitions, respectively. An estimated (4±1)% of the surface-trapped positrons annihilate with Ge 3p–level electrons. The sensitivity of PAES to the surface condition is demonstrated. The PAES yield from a Ge(100) surface is reduced at elevated temperatures, in accord with an activation process earlier found in several positronium (Ps) -fraction experiments. A desorption model adopted from these studies does not describe accurately the PAES results at higher temperatures (>500 °C), where the PAES intensity levels off to 5% of the room-temperature value. Possible sources for the discrepancy are discussed and models for positron trapping to deep surface traps are introduced. On the Ge(100) surface, an upper limit for Ps emission near the melting point is 97%. The error in calibration parameters due to the earlier assumption of 100% Ps emission seems to introduce only small errors into the Ps-fraction measurements.