Heterostructures of pseudomorphic Ge1-yCy and Ge1-x-ySixCy alloys grown on Ge (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 epitaxy (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:solution x-ray diffraction reveals that the layers are pseudomorphic and have high crystalline quality and interface abruptness, evident from strong Pendellosung fringes and superlattice satellite peaks. The heterostructures are 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 defects, We empirically determined the activation energies for the decrease of 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 photoluminescence is observed from pseudomorphic Ge1-yCy samples. (C) 2000 American Vacuum Society.