Photoluminescence and double-crystal x-ray study of InGaAs/InP: Effect of mismatch strain on band gap

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Abstract
Epitaxial layers of InGaAs on InP are the building blocks in optoelectronic device fabrication, where the dependence of the band gap on composition is utilized in device design. The band gap can be determined from the photoluminescence peak energy and composition from lattice size. This work reports a detailed correlation between both the room-temperature (300 K), and low-temperature (7 K) photoluminescence peak energy of epitaxial InGaAs, and the lattice mismatch relative to InP as measured by x-ray double-crystal diffraction. Nominally undoped 1- and 2-μm-thick layers of high quality InGaAs were grown on InP (001) by metalorganic chemical vapor deposition. The relaxed mismatch for these coherent layers was between −0.18% and 0.12%. The observed dependence of the 7-K photoluminescence energy on lattice mismatch confirms the theory of People [Appl. Phys. Lett. 50, 1604 (1987); Phys. Rev. B 32, 1405 (1985)] and Kuo et al. [J. Appl. Phys. 57, 5428 (1985)] which includes the effect of strain on the J= (3)/(2) valence band. The 7 K photoluminescence energy of zero mismatch InGaAs grown on semi-insulating InP substrates ([Fe]=1016 cm−3) was 0.804±0.002 eV and of zero mismatch InGaAs grown on n-type ([S]=2×1019 cm−3) substrates was 0.801±0.002 eV. This difference is attributed to the difference in absolute lattice constant for the two types of substrates. The correlation was extended to room-temperature photo- luminescence where the peak recombination energy depends on the excitation conditions. Simple spectral line-shape analysis showed that the λ 1/2 max (taken from the low-energy side of the peak) was a reliable figure of merit and could be used to estimate the degree of lattice mismatch independent of excitation conditions. This algorithm is applied to the nondestructive mapping of whole wafers.