Effect of Growth Rate On Strain Relaxation and Mobility In Modulation-Doped Si/SiGe Heterostructures

In this letter, we report on the effect of growth rate on the generation of dislocations and on the amount of strain relaxation in graded-Ge Si/SiGe buffer layers. A four-fold difference in growth rate at a given growth temperature is achieved by changing the gas flow rate. Within this range we find the density of misfit segments to decrease more than twenty times for the higher growth rate. Strain relaxation is deduced from the carrier density in a modulation-doped strained Si channel, and shows a significant reduction for the buffer grown at a fast growth rate. Reducing the growth rate of the strained Si channel results in enhanced dislocation glide, which causes a degradation in electron mobility.