Improved compositional uniformity of InGaAsP grown by MOCVD through modification of the susceptor temperature profile

Abstract

The uniformity of InGaAsP layers is becoming increasingly important for optoelectronic devices. We present the results of an investigation where the susceptor temperature profile of a horizontal MOCVD reactor with substrate rotation is modified to achieve enhanced uniformity. Radial variations in room temperature photoluminescence (RTPL) peak wavelength were reduced from over 15 nm variation from center to edge (1 in. radius) to less than 6 nm variation using this technique. Similar improvements of lattice-mismatch (LMM) deviation were also observed. InGaAsP layers with band-gap wavelengths of both 1.1 μm (1.1 Q) and 1.4 μm (1.4 Q) were used to study the effect of the required As/P ratio on the temperature compensation technique. The results displayed that although the more difficult to control 1.1 Q responded more readily to the temperature profile modification, excellent uniformity (<6 nm variation) was achieved for both compositions. Combined RTPL and X-ray diffraction (XRD) measurements, used to evaluate the uniformity improvements of Group III and V sublattices separately, showed that the homogeneity of not only the As solid mole fraction ( y), but the Ga solid mole fraction ( x) benefited as well from the modified temperature profile. Accompanying the experimental observations, current theory on MOCVD growth of InGaAsP is applied to a state-of-the-art reactor to explain the source of the nonuniformities observed, their sensitivity to the reactor environment, and how their magnitude was reduced using the proper temperature profile.