Structural properties of Ga_xIn_1-xAs{plus 45 degree rule}Al_yIn_1-y As multiple layers

Multilayer Ga_xIn_1-xAs/Al_yIn_1-yAs structures grown on InP substrate by molecular beam epitaxy are studied by means of double-crystal X-ray diffraction (DCXD), transmission electron microscopy (TEM), and photoluminescence spectroscopy. The computer simulation of the DCXD curve of the thin modulation-doped single-quantum-well structure ( ∼ 300 nm in total thickness) reveals that it has a very high crystalline perfection. But for a PIN-diode structure of ∼2 μm in total thickness, the DCXD spectrum shows broad peaks. The TEM image of the latter structure reveals many dislocations. The comparison between the thick doped- and undoped-Al_yIn_1-yAs layers suggests that the heavy doping can be one of the causes of the high density of dislocations.