Heterostructures of pseudomorphic Ge1-yCy and Ge1-x-ySixCy alloys grown onGe (001) substrates

Heterostructures of Ge1-yCy and Ge1-x-ySixCy on Ge (001) substratcs with (0 <y<0.001) and (0<x<0.05) were grown by low temperature molecular beam epita xy (T-growth = 275 degrees C). These carbon fractions exceed by nearly ten orders of magnitude the solid solubility of C in bulk germanium. High rt:so lution x-ray diffraction reveals that the layers are pseudomorphic and have high crystalline quality and interface abruptness, evident from strong Pen dellosung fringes and superlattice satellite peaks. The heterostructures ar e metastable due to the supersaturation of substitutional C in the lattice and the strained layers relax at high temperatures. From x-ray diffraction measurements, we conclude that the relaxation mechanism is due to the loss of C from substitutional sites, rather than by the formation of extended de fects, We empirically determined the activation energies for the decrease o f substitutional C in pseudomorphic Ge0.999C0.001 and Ge0.972Si0.027C0.0008 alloys to be 3.4 and 3.6 eV, respectively. Near band-edge photoluminescenc e is observed from pseudomorphic Ge1-yCy samples. (C) 2000 American Vacuum Society.