Comparison between optical and structural properties of ZnSe/GaAs(001) heterostructures grown by MBE under different beam pressure ratios

Optical absorption and photoluminescence (PL) spectroscopy in conjunction with double-crystal x-ray diffraction (DCXRD) analysis were employed to characterize ZnSe/GaAs(001) heterostructures grown by molecular beam epitaxy under different beam pressure ratios (BPR) to study how the stoichiometric conditions alter the optical and structural properties of the ZnSe/GaAs heterojunctions. Two sets of samples were studied, in the first one the ZnSe epilayer being interely grown under different BPR values, whilst in the second set of samples only the initial 3-4 monolayers were grown under different BPRs, the following 1.5 mu m thick ZnSe layer being grown under stoichiometric conditions (BPR=1.0). The near-band edge absorption and photoluminescence spectra of the first set of samples show that among all different BPR values used, the sample grown in stoichiometric conditions exhibits the sharpest and strongest excitonic features. Furthermore, the appearance of a weak emission Line in the low energy region of the PL spectrum (the so-called Y-line at 2.6 eV, ascribed in the Literature to the occurrence of dislocations) and the small FWHM values of the ZnSe DCXRD peaks, show that these stoichiometric growth conditions give rise to both good optical and structural quality. Similarly, the analysis performed on the second set of samples shows that the good crystalline and optical quality of the ZnSe layers grown on top of the control interface layer is retained, indicating that it is possible to tailor the ZnSe/GaAs heterostructure valence band offset by controlling the ZnSe interface stoichiometry, without affecting the optical and structural quality of the aftergrown material.