Gas-source molecular beam epitaxy of SiGe virtual substrates: I. Growth kinetics and doping

Abstract

We have studied the growth by gas-source molecular beam epitaxy (GS-MBE) of SiGe virtual substrates. We have first determined the relationship existing between the Ge concentration in SiGe thick films and the gas phase ratio of disilane and germane, and its behaviour versus growth temperature. We find that Si atoms are 4.6 times more likely to be incorporated than Ge atoms at 550 • C. This incorporation probability decreases as the growth temperature increases, following a thermally activated law with a 0.082-0.126 eV characteristic energy. The dependence of SiGe growth rate on substrate temperatures has a cross-over point at approximately 8% of Ge, above which the growth rate decreases significantly as the temperature increases. Otherwise, we show what p-type or n-type doping levels are typically achievable in SiGe virtual substrates, and the influence diluted diborane and arsine have on the growth kinetics of SiGe. Additionally, we demonstrate that the 'pre-build-up/flash-off' technique originally proposed by Iyer et al for solid-source MBE (1981 J. Appl. Phys. 52 5608) yields abrupt arsenic doping profiles in GS-MBE.

Low temperature growth kinetics of high Ge content SiGe in reduced pressure-chemical vapor deposition

“…No clear-cut transition occurs as we switch from constant F(SiH 2 Cl 2 )/ F(H 2 ) MFR data points to constant F(GeH 4 )/F(H 2 ) MFR data points, by contrast to the Ge concentration. Such a bell-like shape evolution of the SiGe growth rate as the Ge concentration increases is akin to the one observed for SiGe layers grown with a SiH 4 +GeH 4 chemistry in RP-CVD [23] or very low pressure CVD [24] or with a Si 2 H 6 +GeH 4 chemistry in gas source-molecular beam epitaxy [25]. The increase of the SiGe growth rate for low Ge concentrations was explained in terms of a lowering of the surface coverage by hydrogen when Ge atoms are present on the surface.…”

“…[24] and 8% in Ref. [25]). The saturation then the decrease of the SiGe growth rate occurs in our case for a constant F(GeH 4 )/F(H 2 ) MFR and decreasing F(SiH 2 Cl 2 )/F(H 2 ) MFRs, i.e.…”

Strain relaxation in high Ge content SiGe layers deposited on Si

“…As a matter of fact, the existence of this large mismatch, combined with the difference in surface energies, results in a growth process where the Ge-rich alloy coalesces in three dimensional islands according to the Stranski-Krastanov mechanism, if growth conditions close to thermodynamic equilibrium are maintained. 13,14 It should be mentioned, though, that it was recently demonstrated 15 that the growth rate limitations can be successfully circumvented by using plasma-enhanced CVD, which allows high deposition rates. 11,12 While this method has been widely reported for low ͑x Ͻ 0.5͒ Ge content, for final composition in the high Ge content range the thickness to be deposited is so large ͑ϳ10-20 m͒ that the growth of high quality materials is both impractical and very difficult to achieve with standard deposition techniques, such as chemical vapor deposition ͑CVD͒ and molecular beam epitaxy.…”

Terrace grading of SiGe for high-quality virtual substrates

“…X-ray diffractometry ͑XRD͒ was carried out in order to confirm the germanium composition and state of relaxation. 7 The XTEM micrographs of the samples LG1 and TG1 are shown in Fig. 1.…”