High-mobility two-dimensional electron gases in Si/SiGe heterostructures on relaxed SiGe layers grown at high temperature

Abstract

Low-temperature mobilities for two-dimensional electron gases (2DEGs) formed in tensile-strained Si/SiGe heterostructures are reported, with values up to 2.7 × 10 5 cm 2 V −1 s −1 for a density of 4.6 × 10 11 cm −2 electrons. The strained layers were grown at 600 • C in a ultra-high-vacuum chemical vapour deposition system using SiH 4 and GeH 4 operating at around 20 Pa. The surface morphology of the layers is also discussed and both the mobility and morphology are linked to the quality of the virtual substrates. The virtual substrate consists of strain-relaxed SiGe alloys grown on Si(001) substrates; we show that it is preferable to grow these substrates at higher temperatures and higher growth rates. For low growth rates and temperatures the 2DEG mobility as a function of sheet carrier density was found to be degraded.

Negative Magnetoresistivity from Electron-Electron Interaction Effect in Modulation Doped n-Channel Si/Si1?xGex Quantum Well Structures

“…The low temperature mobility values are less readily related to room temperature transport, since optical phonon scattering becomes significant above $100 K. Nevertheless, the magnitude can be taken as indicator of overall material quality, including such factors as the background doping level in Si channel, the interface roughness between this channel and the SiGe barriers, and possible Ge and As segregation effects. Although the results obtained here are not up to the level of over 10 5 cm 2 /Vs reported by others [16,17], they are completely acceptable for device applications. The ratio of transport to quantum relaxation time, t t /t q , is close to 7-9 for both samples, showing the expected dominance of small-angle remote impurity scattering [18].…”

High-performance nMOSFETs using a novel strained Si/SiGe CMOS architecture

“…The Si/SiGe layers were grown by low-pressure chemical vapor deposition in an Applied Materials Centura tool using SiH and GeH in a H carrier gas with B H for p-type doping [18], [19]. The 1-m constant composition Si Ge VS and the preceding graded Si…”

MOS gated Si:SiGe quantum wells formed by anodic oxidation

“…The starting substrate was a p-type, [10][11][12][13][14][15][16][17][18][19][20] cm Si wafer, on which a 1 µm linearly graded SiGe buffer was grown. The Ge content in the buffer was increased linearly from 5% to 25%.…”

“…We have fitted the data in figure 3 to equation (1) and the values of N back are given in [17] using ungated samples with different sheet densities.…”