X-ray characterization of In_xGa_1-xAs/GaAs quantum wells

X-ray diffraction patterns have been measured for pseudomorphic In_xGa_1-xAs/GaAs quantum well (QW) structures of widths 183, 121 and 61 {right parenthesis, less than}, and composition x of about 0.28 grown by molecular beam epitaxy. The measured patterns show Pendellösung fringes due to the 513 {right parenthesis, less than} GaAs barriers. These Pendellösung fringes are modulated by a broad weak peak mostly coming from the 183 Å In_xGa_1-xAs well layer. The X-ray diffraction fringe modulating patterns between 32° and 33° are fairly symmetric for a non-interrupted growth procedure. The diffraction pattern for the same structures with interrupted growth is less symmetric, since there is further modulation by another weaker peak. This shows that the In_xGa_1-xAs well layers have less well controlled In composition if grown with interruption times of tens of seconds at each interface. The thickest In_xGa_1-xAs well layer exhibits the highest In composition. Layer thickness and In composition in thin layers (around 100 {right parenthesis, less than} in the thickness) can be estimated by X-ray modeling and good agreement obtained between the measured and the calculated X-ray diffraction patterns.