Strain-relaxed compositionally graded InGaP layers grown by atmospheric-pressure metalorganic vapor phase epitaxy had previously been found to exhibit unusual contrast in transmission electron microscopy. The features that generated this contrast were termed so-called branch defects. Such defects were shown to pin threading dislocations and were thus undesirable features for the realization of low dislocation density semiconductors. The properties of branch defects formed during optimized, relaxed, graded InGaP buffer deposition in 2 different reactor configurations were compared here. These were a commercial multi-wafer low-pressure reactor, and a custom-built atmospheric-pressure research reactor. Branch defect formation was further characterized via the introduction of in situ annealing interruptions during graded buffer deposition in the atmospheric-pressure system. Branch defects were observed in material from both reactor systems, suggesting that they were a phenomenon intrinsic to InGaP graded buffer growth. Careful transmission electron microscopic studies of the resulting samples revealed that the phase space for the formation of branch defects was similar in both reactor configurations. During standard optimized graded buffer growth, higher growth temperatures delay the onset of branch defect formation to higher In fractions in the graded buffer. Low growth temperatures produce branch defects at lower In fractions, and these defects tend to be more closely spaced. In addition, the formation of branch defects was favored by low V/III ratios and in situ growth interruption and annealing. Annealing was found to create anisotropic strain relaxation in the graded buffer, which was attributed to the blocking of gliding threading dislocations by preferentially oriented branch defects. Based upon the observed properties of branch defects and the factors that affect their formation, it appears that these defects were a manifestation of local variations in In concentration that develop on the sample surface during metalorganic vapor-phase epitaxy and were buried in the bulk due to kinetic limitations.

Microstructural Defects in Metalorganic Vapor Phase Epitaxy of Relaxed Graded InGaP - Branch Defect Origins and Engineering. L.M.McGill, E.A.Fitzgerald, A.Y.Kim, J.W.Huang, S.S.Yi, P.N.Grillot, S.A.Stockman: Journal of Vacuum Science & Technology B, 2004, 22[4], 1899-911