Hole effective mass in strained Si1-xCx alloys.

The directional, density-of-states, and carrier-concentration effective masses of light, heavy, and split-off holes have been calculated for strained Si1-xCx alloys on Si (001) substrate. The results for the directional effective mass show that the effect of strain makes the constant energy surface of light holes near the band edge more symmetric than that in pure silicon. The effect of strain on the heavy and split-off hole bands is rather regular; up to 7% of carbon concentration the strain effect monotonically reduces the density-of-states effective mass for the two bands at energy values within energy interval of 0.4 eV below the valence band edge. This reduction is obtained for the carrier-concentration effective mass at temperatures from 0 to 600 K. The strain effect on the light hole band is less trivial; at nonzero carbon concentrations the strain effect influences the density-of-states and the carrier-concentration effective mass in a similar way as it does to the heavy and split-off bands but irregular behavior shows up in the energy interval of 0.02 eV below the valence band edge and at the temperature range from 0 to 140 K. At 7% of carbon doping the total density-of-states effective mass for holes at 77 and 300 K are almost the same, namely, the values are 0.39 and 0.40 in units of free electron mass, respectively. [ABSTRACT FROM AUTHOR]