Investigations of electron-beam and optical induced damage in high mobility SiGe heterostructures

Modulation-doped two dimensional electron gases (2DEGs) grown on Si0.7Ge0.3 virtual substrates were investigated. Low temperature measurements were used to characterise the uniformity of the wafers and annealing studies demonstrated that high annealing temperatures (above 600 degrees C) destroyed the electrical properties. Studies of excimer irradiation of the 2DEG material demonstrated that only surface damage was induced, but the subsequent annealing of this damage reduced the carrier density in the material, suggesting strain relaxation of the strained Si cap. Electron beam irradiation experiments at 40 keV and PMMA doses showed charging effects at room temperature but little damage. Finally a number of narrow channel devices were fabricated using 300 keV electrons and characterised at low temperature to estimate the range of the electron-beam induced damage. (C) 1997 Elsevier Science Ltd.