Effect of substrate polarity on the optical and vibrational properties of (311)A and (311) B oriented InAlAs/InP heterostructures

In this report, we use the photoluminescence (PL) and micro-Raman scattering techniques to systematically study the optical and vibrational properties of InAlAs/InP heterostructures grown by metal organic chemical vapor deposition (MOCVD) on either Indium (A-face) or Phosphorous (B-face) terminated (311) oriented substrates. PL measurements show that the InAlAs band gap redshifts with sample polarity switching from B to A, which is attributed to the change of the indium composition with substrate polarity. Then, micro-Raman investigations have been realized with the aim to comprehend the influence of substrate polarity on the shifts in phonon frequencies in Raman spectra. By using the modified random-element-isodisplacement (MREI) theory, we have explained the alloying effect in the In_xAl_1-xAs layers. A good consistency between InAs and AlAs-like phonon frequencies from the fitting of Raman spectra and calculated is achieved. AlAs-like LO phonon frequency has been employed to calculate the In composition and residual strain in our samples. In addition, the In composition of the In_xAl_1-xAs layer has been also determined by PL measurements. A good agreement with the indium contents obtained by both methods and those measured during growth of the epilayers has been attained. Our findings suggest that optical and crystalline quality are better for the (311)A sample.