Very low temperature growth of GeSi alloys with digermane, disilane and dichlorosilane

Abstract

GeSn/GeSi multi quantum wells with (i) high Sn content, direct bandgap GeSn wells and (ii) GeSi barriers with Si contents in the few %–30% range might be of use in optoelectronics. As GeSn has to be grown in the 300–375 °C range (to avoid Sn segregation/precipitation), GeSi barriers should also be grown in that temperature range, too. GeSi might also be used to passivate, at low temperatures, the surface of Ge-rich imagers and photo-detectors. Thanks to X-Ray Reflectivity (thickness) and X-Ray Diffraction (Si content), I have therefore explored, in a 200 mm Chemical Vapour Deposition tool, the 100 Torr growth of tens of nm thick GeSi layers on Ge(001) buffers. Precursor gases were Ge2H6 (Ge), SiH2Cl2 and/or Si2H6 (Si). Whatever the chemistry, a temperature increase in the 350–500 °C range resulted in an increase, (a stabilization) then a decrease of the GeSi growth rate. Meanwhile, the Si content increased almost linearly with the temperature. For given Si and Ge flows, GeSi growth rates were higher and Si contents lower with SiH2Cl2 than with Si2H6. Adding SiH2Cl2 to Si2H6 had, quite surprisingly, almost no impact on the GeSi growth kinetics, which was mainly governed by the Si2H6 flow. With high precursor flows, I succeeded in having, with Ge2H6 and SiH2Cl2, GeSi growth rates increasing from 2 up to 32 nm min−1 as the temperature increased from 325 °C up to 375 °C, with a Si content close to 7.5%. Growth rates increased from 0.6 up to 19 nm min−1 and Si contents decreased from 24 down to 22% over the same temperature range with Ge2H6, SiH2Cl2 and Si2H6.