High mobility electron gases and modulation-doped field effect transistors fabricated in Si/Si1−xGex by rapid thermal chemical vapor deposition

Abstract

High mobility n-type Si0.62Ge0.38/strained Si modulation-doped structures have been fabricated on relaxed graded Si1−xGex buffers by rapid thermal chemical vapor deposition. The mobility and density of the two-dimensional electron gas was studied as a function of spacer thickness of the modulation-doped structure. Mobilities exceeding 40 000 cm2/V s at a density of 1.7×1012 cm−2 (10 K) and 15 000 cm2/V s at a density of 2.9×1012 cm−2 (77 K) were observed, giving a record low sheet resistivity of 140 Ω/⧠ at 77 K. Self-aligned depletion and enhancement mode modulation-doped field effect transistors were fabricated in similar structures using a novel two-step lithography process. Good saturation characteristics with low gate leakage currents were achieved, but the maximum room-temperature transconductance was limited by parasitic source and drain resistances.