Composition modulation in GaInNAs quantum wells: Comparison of experiment and theory

Abstract

Composition modulation observed in GaInNAs quantum wells imposes an important handicap to their potential application within optical components, particularly as the indium and nitrogen contents are increased to reach longer wavelengths. In this paper, we compare our experimental results of phase separation in GaInNAs quantum wells grown at different temperatures with recent theoretical models of spinodal decomposition from the literature. This comparison has shown that the regular solution approximation, which explains the higher composition modulation compared to GaInAs samples, provides a more appropriate explanation of GaInNAs decomposition than the usual delta lattice-parameter approximation. Transmission electron microscopy shows no composition modulation contrasts with the chemical sensitive 002 dark field reflection and a strong increase in the intensity of the strain contrasts observed with 220 bright field reflection as the growth temperature increases from 360to460°C. These observations can be explained by an uncoupling between N and In composition profiles forming separate In-rich and N-rich regions according to the regular solution approximation model. We therefore believe that the compositional fluctuations in GaInNAs are not only due to GaInAs decomposition, but that an uncoupled modulation of the III and V elements is also present.

Charge separation and temperature-induced carrier migration in Ga1−xInxNNuytten1, Hayne2, Bansal3 et al. 2011Phys. Rev. BSelf Cite

“…In other words, at low T the electrons and the holes are being localized at different locations by nitrogen-and indium-rich regions, respectively, but the separation is larger in Sample B, which was grown under optimized conditions, compared to Sample A. Our results clearly corroborate the localization picture as established by TEM in similar samples: [27][28][29][30] the spatial separation between the electrons and the holes imposed by the disorder-induced local minima in the potential profile is more pronounced in the sample grown at lower temperature due to the increase in the period between composition modulations. In contrast, the activation energy required to free the carriers and recover the free-exciton wave-function extent is smaller than in the samples grown at 045302-5 higher T due to the shallower localization potentials: Sample B, which was grown at 325…”

“…[27][28][29][30] Transmission electron microscopy (TEM) studies performed by Herrera et al [28][29][30] indicate that an increase in growth temperature enhances In/Ga interdiffusion during growth, which leads to TEM-observable composition fluctuations in the structure. The phase separation between the group-III elements leads to the coexistence of two independent composition profiles for In and N, which are out of phase.…”

Kinetic considerations on the phase separation of GaInNAs quantum wells

“…We have found that, in order to observe a uniform contrast in the image of a GaInNAs www.pss-c.com quantum well with g002DF, it is necessary that each increase in the N composition, ∆y, comes accompanied by a simultaneous decrease in the In content, ∆x, in an approximate proportion of ∆x ≈ -2.2∆y. Therefore, the composition fluctuations in the studied quantum wells should consist of alternate areas rich in In and poor in N, and vice versa [5], which explains the high intensity of the strain contrasts found with 220BF in these structures.…”

“…This result is related to the fact that we are considering a quaternary alloy, and the composition of the system can fluctuate in the group III sublattice and also in the group V one. We have analyzed the dependence of the structure factors of Ga 1-x In x N y As alloy for the In and N compositions and this analysis can be found elsewhere [5]. We have found that, in order to observe a uniform contrast in the image of a GaInNAs www.pss-c.com quantum well with g002DF, it is necessary that each increase in the N composition, ∆y, comes accompanied by a simultaneous decrease in the In content, ∆x, in an approximate proportion of ∆x ≈ -2.2∆y.…”

Electro‐modulation enhancement in the InGaNAs/GaAs quantum well structures

“…Besides, adding nitrogen not only increase the conduction band offset but also compensate the layer compressive strain induced by In. However, large N mole fraction is found to increase threshold current density and degrade the optical and structural properties [7,8]. Considering that the In and N induce opposite effect on the lattice constant and influence similarly in reducing the band gap energy, a desirable composition ratio of this quaternary compound is continuously sought to achieve further improvement and better performance in the active layer.…”