Impact of flows, temperature and pressure on the GeSn growth kinetics with a digermane and tin tetrachloride chemistry

We have systematically quantified, for a fixed Ge2H6 flow, the impact of temperature, pressure, H2 carrier flow and SnCl4 flow on the GeSn growth kinetics in Reduced Pressure - Chemical Vapor Deposition (RP-CVD). We have shown that the growth temperature T was the main lever that should be actioned in order to change the Sn concentration, with, at 100 Torr, a-1.55 %/10 degrees C decrease as T increased over the 301 degrees C-362 degrees C range. We had, as expected, an exponential increase of the GeSn growth rate with T, with very similar activation energies between 11.0 and 11.6 kcal mol.-1 whatever the SnCl4 flow. Changing, at a given temperature, the SnCl4 flow resulted in a Sn concentration increase of, on average, 2.6 % only for a factor of three increase of the SnCl4 flow. Growth rates, which linearly increased with the SnCl4 flows, were however rather small for small SnCl4 flows, which would be a hindrance for thick stacks. We had, at 100 Torr, a slight Sn concentration increase when halving the reference H2 flow, but the gain was limited (on average, +1.36 % over the 313 degrees C-362 degrees C range) and the spatial uniformity degraded. A halving of the growth pressure from 100 down to 50 Torr otherwise resulted in Sn concentrations that were barely lower (-0.65 % only, on average). Finally, layers grown in the 301 degrees C-349 degrees C range were cross-hatched and of high crystalline quality, while 362 degrees C layers were islanded, all the more so for low SnCl4 flows.