Relaxed Si0.7Ge0.3 layers grown on low-temperature Si buffers with low threading dislocation density

${\mathrm{Si}}_{\mathrm{0.7}}{\mathrm{Ge}}_{\mathrm{0.3}}$ epilayers with low threading dislocation density have been grown on Si (001) substrates by introducing a low temperature Si buffer. Such a structure can be used as the buffer for the growth of device structures. In comparison with the conventional compositionally graded buffer system, it has the advantages of having lower threading dislocation density, smaller thickness for required degree of relaxation, and smoother surface. Experimental evidence suggests that an anomalous relaxation mechanism has been involved.