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The growth temperature of spacer layers (SPLs) is investigated as a means to obtain identical layers for multilayer quantum dot (QD) structures. A 5-layer 1.3-μm InAs∕GaAs QD structure with 50-nm GaAs SPLs served as a model system. It is found that the growth temperature of the GaAs SPLs has pronounced effects on both the structural and optical properties of the InAs QDs. For GaAs SPLs grown at a low temperature of 510°C, dislocations are observed in the second and subsequent layers, a result of significant surface roughness in the underlying spacer layer. However by increasing the growth temperature to 580°C for the final 35nm of the 50-nm GaAs SPLs, a much smoother surface is achieved, allowing the fabrication of essentially identical, defect free QD layers. The suppression of defect formation enhances both the room-temperature photoluminescence efficiency and the performance of 1.3-μm multilayer InAs∕GaAs QD lasers. An extremely low continue-wave room-temperature threshold current density of 39A∕cm2 is...

A study by transmission electron microscopy of the influence of the In and N contents in the ranges of 20%–35% and 1.1%–3%, respectively, on the microstructure of Ga1−xInxNyAs1−y quantum wells is presented. Frank dislocation loops characterized as extrinsic have been found in the samples with x⩾0.25. In these structures, threading dislocations appear as a consequence of the unfaulting of the loops for y⩾0.014. An analysis of the density and size of the dislocation loops has provided an estimation of the critical radius for the unfaulting process. A model for this critical radius of the unfaulting process of extrinsic Frank loops is proposed. From this model and experimental values of critical radius, an estimation of the stacking fault energy of the GaInNAs alloy has been made. We have found a reduction in the stacking fault energy of the GaInNAs alloys when increasing the N content from 1.4% to 2.3% in good agreement with the theoretical estimation of the stacking fault energies of zinc-blende GaN and InN.

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 e...