Threading dislocations and phase separation in InGaAs layers on GaAs substrates grown by low-temperature metalorganic vapor phase epitaxy

InGaAs layers with In composition between 0.50 and 0.57 were grown on GaAs substrates with graded buffer layers at temperatures between 370 and 470 degrees C by metalorganic vapor phase epitaxy. Periodic structure resulting from phase separation was observed in the cap layers grown at 450 and 470 degrees C by transmission electron microscopy (TEM). Threading dislocation densities in the cap layer grown at 450 degrees C were determined to be 6.7 x 10(7), 5.7 x 10(7), and 8.1 x 10(8) cm(-2) using 1 mu m graded buffer layers on an exactly oriented substrate, on a substrate misoriented toward (11 I)A and on that misoriented toward (I I I)B by plan-view TEM, respectively. The periodic structure depended on the substrate misorientation. The structure was correlated with surface morphology. The structure blocked dislocation propagation in the layers. The growth temperature was lowered below 450 degrees C using triethylgallium instead of trimethylgallium as the Ga source. No phase separation was found for layers grown at 370 and 400 degrees C with TEM. Threading dislocation densities in the cap layer grown at 400 degrees C were as low as 7.1 X 10(6), 1.7 x 10(7) and 1.7 x 10(7) cm(-2), for an exactly oriented substrate, a substrate misoriented toward (1 1 1)A and that misoriented toward (111)13, respectively. Low-temperature growth at around 400 degrees C was effective in achieving homogeneous InGaAs layers with a low threading dislocation density.