Growth and mechanical properties of GeSi bulk crystals

Bulk crystals of Ge_1–xSi _x alloys were grown by the Czochralski technique. Full single crystals were obtained for the alloys of composition 0 < x < 0.15 and 0.9 < x < 1, while single crystal parts near the seeds of ingots provided alloys of intermediate composition. The dislocation velocity and mechanical strength of the GeSi alloys were investigated by the etch pit technique and compressive deformation tests, respectively. In the GeSi alloys of the composition range 0.004 < x < 0.080 the dislocation velocity decreases monotonically with increasing Si content in the temperature range 450–700°C and the stress range 3–24 MPa. In contrast, in the composition range 0.94 < x < 1 the dislocation velocity first increases and then decreases with decreasing Si content in the temperature range 750–850°C and the stress range 3–30 MPa. The velocity of dislocations was determined as functions of stress and temperature. The stress–strain behaviour in the yield region of the GeSi alloys of composition 0 < x < 0.4 is similar to that of Ge at temperatures lower than about 600°C. However, the yield stress becomes temperature-insensitive at high temperatures and increases with increasing Si content. The stress–strain curves of the GeSi alloys of composition 0.94 < x < 1 are similar to those of pure Si at temperatures of 800–1000°C and the yield stress increases with decreasing Si content down to x = 0.94. The yield stress of the GeSi alloys is dependent on the composition, being proportional to x(1 – x). The strengthening mechanism in alloy semiconductors is discussed.