Optical properties of compositionally graded InxAl1–xAs/GaAs heterostructures

We report the photoluminescence (PL) properties of compositionally graded InxAl1–xAs (0.13 < x < xc) lattice mismatched heterostructures grown on GaAs substrates by Molecular Beam Epitaxy (MBE). Two series of epilayers (xc = 0.34 and xc = 0.37) were examined in this work by photoluminescence, including step graded and various doping concentrations. At room temperature, the PL spectra of the two samples show the presence of an intense band B attributed to band–band transition in InAlAs active layer. At low temperature (T < 200 K), a broad band labelled C appears instead of band B in the PL spectra of the tow samples. This band which is 0.3 eV below the conduction band of the active layer corresponds to the radiative recombination from both native defects during growth and deep levels in InAlAs as DX centers. The PL line width of the band C increases with temperature in both samples. The PL peak of GaAs substrate was buried by other bands when the indium composition and the doping concentration increase.