Determination of refractive index and direct bandgap of lattice matched BGaP and (BGa)(AsP) materials on exact oriented silicon

Abstract

High quality lattice matched III-V semiconductor material, boron gallium phosphide (B2.8%Ga)P and boron gallium arsenide phosphide (BGa)(AsP), layers were deposited on exact oriented (001) 300 mm silicon (Si) substrates by metal organic chemical vapor deposition. An industrial Aixtron Crius R (CCS close coupled showerhead) 300 mm system was used. The material compositions were varied systematically to keep the lattice match to the silicon substrate on one hand, but to change the optical properties and thereby investigate the relationship between the refractive index and different material compositions on the other hand. By in situ measurements, the reflectance was measured during growth, and the refractive index for the wavelength of λ = 950 nm was determined. The results are compared and confirmed with the measurement results of Rogowsky et al. [J. Appl. Phys. 109, 053504 (2011)] which had been achieved by ellipsometry and show a linear dependence in relation to the arsenide and boron content. The refractive index of B2.8%GaP is found to be 3.14, and therefore is larger than the refractive index of GaP of 3.13. This confirms former investigations which lead to the conclusion that the direct band gap of B2.8%GaP is smaller than the direct band gap of GaP. The refractive index of B6.2%GaAs15%P is found to be 3.20, which is a change of 2.3% in comparison to GaP. Based on the measurement results of the direct band gap of BGaP samples with a boron content of up to 6% by surface photo voltage, the direct band gaps of the (BGa)(AsP) samples were calculated and related to the refractive index values. As a result, a change of 2% in the refractive index relates to a reduction of 400 meV in the direct band gap of (BGa)(AsP).