Hole mobility enhancements in nanometer-scale strained-silicon heterostructures grown on Ge-rich relaxed Si1−xGex

Abstract

Although strained-silicon (ε-Si) p-type metal–oxide–semiconductor field-effect transistors (p-MOSFETs) demonstrate enhanced hole mobility compared to bulk Si devices, the enhancement has widely been observed to degrade at large vertical effective fields. We conjecture that the hole wave function in ε-Si heterostructures spreads out over distances of ∼10 nm, even at large inversion densities, due to the strain-induced reduction of the out-of-plane effective mass. Relevant experimental and theoretical studies supporting this argument are presented. We further hypothesize that by growing layers thinner than the hole wave function itself, inversion carriers can be forced to occupy and hybridize the valence bands of different materials. In this article, we show that p-MOSFETs with thin (i.e., <3 nm) ε-Si layers grown on Ge-rich Si1−xGex buffers exhibit markedly different mobility enhancements from prior ε-Si p-MOSFETs. Devices fabricated on a thin ε-Si layer grown on relaxed Si0.3Ge0.7 demonstrate hole mobility enhancements that increase with gate overdrive, peaking at a value of nearly 3 times. In other devices where the channel region consists of a periodic ε-Si/relaxed Si0.3Ge0.7 digital alloy, a nearly constant mobility enhancement of 2.0 was observed over inversion densities ranging from 3 to 14×1012/cm2.

Selective epitaxy growth of Si1−xGex layers for MOSFETs and FinFETs

“…However, most of these works demonstrated the hole mobility improvement was degraded to a near zero at large vertical electric field [4,22,23] (where this is the operating range of commercial MOSFETs) as shown in Fig. 2.…”

Tailoring of Interfaces for the Photoelectrochemical Conversion of Solar Energy

“…The side view (Figure 2.58 a) shows initially formed oxide islands which grow into the Si substrate but also extend towards the exterior of the geometrical surface, due to the volume mismatch of 2.27 between the oxide and Si. The oxide is thus under compressive stress whereas Si is underneath the oxide and is under tensile stress, a fact that is important in microelectronic devices [234] . Between oxide islands, the stress in the substrate is compressive as indicated.…”

Enhanced growth of low-resistivity cobalt silicide by using a Co/Au/Co trilayer film on Si0.8Ge0.2 virtual substrate

“…Recently, epitaxial Si 1Àx Ge x alloys on (001)Si have attracted a lot of attention, because Si 1Àx Ge x /Si heterostructures have already been found their potential for applications in many areas such as high-speed nanoelectronics and field effect transistors [1,2]. In these devices applications, it is necessary to form good Ohmic or Schottky contacts with the epitaxial Si 1Àx Ge x substrates.…”