Comparative optical studies of InAlAs/InP quantum wells grown by MOCVD on (311)A and (311)B InP planes

Abstract

We study the optical and vibrational properties of InAlAs alloy films on high-index InP (311)A/B substrate at a wide range of V/III flux ratio (25–125).The crystallinity, vibrational and optical characteristics of InAlAs/InP structures are determined using a combination of photoluminescence (PL) and micro-Raman spectroscopies. Raman studies of InAlAs layer grown on traditional (100)InP substrates show a strong dependence of the optical phonons on V/III molar ratio (Sayari et al. in J Raman Spectrosc 40:1023–1027, 2009). Analysis of PL spectra shows the formation of InAsxP1−x graded layer located at the inverted interface and a broadening of the InAlAs PL band suggests that a clustering effect. Also, a strong dependence of these PL bands on the V/III ratio and substrate polarity is observed and attributed to the clustering effect and to the presence of a strain-induced piezoelectric field. In addition, micro-Raman spectra show a line shape broadening and wave number shift of the Raman peaks for various V/III molar ratios. Furthermore, we discuss the effect laser excitation wavelength on the Raman spectrum. Then, micro-Raman investigations show the presence of an LO mode related to LO-like InAs in InAsP alloy at the inverted interface in our samples. At lower frequencies, disorder-activated longitudinal acoustic phonons are also observed, which considers the presence of potential fluctuations (cluster effect). Finally, by using the modified random-element-iso-displacement theory, we have explained the alloying effect in the InxAl1−xAs layers. A good consistency between calculated and measured InAs and AlAs-like phonon frequencies is obtained. Using the AlAs-like LO phonon frequency shifts, we have calculated the residual strain in the InxAl1−xAs layer. The lower residual strain value is obtained for the (311)A orientation with the lowest V/III ratio and for the (311)B orientation with the largest V/III ratio.