The importance of lattice mismatch in the growth of GaxIn1−xP epitaxial crystals

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Abstract
The importance of lattice‐parameter mismatch between the GaAs substrate and the GaxIn1−xP epitaxial layer on crystal growth and properties has been investigated. Three major effects were observed: (i) The crystal morphology and substrate/epitaxial‐layer interface were found to be nearly perfect for a0 ≈ a0 GaAs and very poor including melt inclusions at the interface for other epitaxial‐layer compositions. (ii) The dislocation density was found to depend on a0 ‐ a0 GaAs varying from 105 to > 108 cm−2. (iii) The excess energy due to lattice‐parameter mismatch was found to perturb the solid composition from the chemical‐equilibrium composition toward the composition which minimizes mismatch; i.e., epitaxial layers with x=0.51±0.01 are grown from Ga–In–P liquids with chemical‐equilibrium solidus compositions ranging from 0.46 to 0.62. The result is that under the growth conditions used, highly perfect epitaxial layers could be grown only near x=0.51 with band gaps near 1.9 eV. Other compositions with EG>1.9 eV were highly imperfect with poor morphology, melt inclusions, and large numbers of dislocations.