Molecular beam epitaxy of metastable, diamond structure SnxGe1−x alloys

Abstract

Single-phase SnxGe1−x alloys with x up to 0.3 have been grown by molecular beam epitaxy. X-ray diffraction measurements indicate the layers to have the diamond crystal structure. The metastability of the alloys is apparent as increases in the growth temperature, layer thickness, or Sn composition cause phase separation of the Sn into a noncubic (white or β-Sn) form. Rutherford backscattering spectrometry and reflection high-energy electron diffraction measurements indicate that the initial stages of growth are complicated. The first several hundred angstroms of growth are compositionally graded, with the Sn incorporation rate increasing with film thickness. Thereafter, the alloy composition remains constant, determined by flux composition, until a critical thickness for phase separation is reached (≂2000 Å for x=0.3).

Group IV Direct Band Gap Photonics: Methods, Challenges, and Opportunities

“…Therefore, the fabrication of high quality and smooth epilayers was a demanding task for many years and the development of new growth processes to deposit GeSn under non-equilibrium conditions at low temperatures was required. Whereas the first attempts to grow GeSn alloys were based on molecular beam epitaxy (MBE) in 1980s and 1990s (Pukite et al, 1989;Harwit et al, 1990;Wegscheider et al, 1990;Fitzgerald et al, 1991;He and Atwater, 1997), device-grade GeSn epilayers could be synthesized since the early 2000s when the first chemical vapor deposition (CVD) processes were developed (Bauer et al, 2003).…”

Growth and applications of GeSn-related group-IV semiconductor materials

“…In the early stages, there were some reports of the MBE growth of Ge 1−x Sn x epitaxial layers on Si or Ge substrates [22][23][24][25][26]. Ge and Sn were usually deposited with Knudsen cells in an ultrahigh vacuum (UHV) chamber.…”

Measurement of the direct energy gap of coherently strained SnxGe1−x/Ge(001) heterostructures

“…Although growth of Sn x Ge 1Ϫx is complicated by a limited bulk solid solubility, xϽ0.005, and a tendency for Sn surface segregation due to a lower Sn surface free energy than Ge, nonequilibrium growth via molecular beam epitaxy can yield supersaturated solid solutions and Sn surface segregation can be controlled with low growth temperatures, TϽ180°C. 1,2 Previously it was demonstrated that homogeneous, strainrelieved Sn x Ge 1Ϫx epitaxial films grown on Si͑001͒ undergo an indirect to direct energy gap transition near xϭ0.09 yielding the first known example of a direct energy gap group IV semiconductor. 3 The direct energy gap varies from 0.35 ϽE g Ͻ0.80 for composition range 0.15ϽxϽ0 for these Sn x Ge 1Ϫx alloy solid solutions.…”