LPE Growth of Misfit Dislocation‐Free Thick In1 − x Ga x As Layers on InP

Abstract

The conditions for equilibrium LPE growth of exactly and nearly lattice-matched Inl-xGaxAs epitaxial layers on InP (100) substrates were determined at 650~ by lattice constant measurements. It was found that the half-width of the diffraction peak of the ternary layer was much smaller than that of an Inl-xGaxAsl-~Py layer, and that the composition of the ternary layer scarcely varied along the thickness. The threshold region for the formation of misfit dislocations into the ternary layers were experimentally determined by using an x-ray topograph. This region can be displayed by both the lattice misfit and the thickness. It was found that the layers thicker than 10 ~m without misfit dislocations could be grown starting from 650~ only when the lattice misfit at room temperature was between-6.5 • 10-4 and-9 • 10-4. It is most important for the growth of misfit dislocation-free thick layers that the layers should be lattice-matched to the substrates at the growth temperature and that tensile stress should not be incurred at the growth temperature. The relationships between the photoluminescence peak wavelength or solid composition and the lattice misfit were determined experimentally. The growth of lattice-matched In0.53Gao.4~As on InP substrates has been investigated mainly to fabricate avalanche photodiodes (APD's) for light whose wavelength lies between 1.0 and 1.65 ~m. Several reports (1-4) were made on the ternary APD's. For the fabrication of optical devices such as APD's, thick and misfit dislocation-free epitaxial layers are required. The thin ternary layers without any misfit dislocations have generally been obtained by exact lattice-matching on the substrates at room temperature. However, we found that misfit dislocations appeared in the exactly lattice-matched thicker In0.53Ga0.47As layers than 4 #m, which were grown by liquid phase epitaxial (LPE) method starting from 650~ These misfit dis-locations are introduced by the interracial stress which is caused by the difference of thermal expansion coefficients between the epitaxial layer and the sub-strates. Therefore, the conditions for the growth of thick and misfit dislocation-free layers must be studied in order to fabricate APD's of In0.53Ga0.47As. Such conditions had ever been determined only for the Gal-=AlxAsl-yPy system on GaAs substrates (5). In this work, the conditions for the growth of the misfit dislocation-free thick In0.53Ga0.47As layers on InP(100) substrates were experimentally determined. Under these conditions, the misfit dislocation-free layers thicker than 10#m could be grown. These results were analyzed. In order to determine the accurate wavelength of the exactly lattice-matched In0.53-Gao.47As on InP, the relationship between the photo-luminescence peak wavelength and the lattice misfit was measured. The composition variations of the layers with distance from the surface of the substrate were also studied. Experimental Procedure and Results LPE growth conditions.~The previously determined liquidus isotherm at 650~ (6) was used to grow Inl-xGaxAs on InP under equilibrium conditions. The conditions for equilibrium LPE growth of exactly and nearly lattice-matched layers on InP (100) substrates were found by lattice constant measurements of these layers grown from melts with compositions On the liquidus isotherms. Supersaturated melts were not used in this growth. Layers were grown starting from 650~ at a constant cooling rate of 0.5~ by the