Interface disorder in AlAs/(Al)GaAs Bragg reflectors

Abstract

We have investigated the structural properties of Bragg reflectors grown by molecular beam epitaxy. The reflectors consist of quarter-wavelength stacks of AlAs/ AlxGa1−xAs. We find a strong dependence of the interface quality on the substrate growth temperature, the Al composition in the ternary alloy, and the presence of impurities in AlAs. We have classified the interface disorder into two categories: interface roughness and structural waviness. We ascribe interface roughness to the segregation of oxygen during AlAs growth. The structural waviness originates from differing surface migration kinetics of Al and Ga which results in phase separation during growth of AlGaAs.

The impact of oxygen incorporation during the MBE growth of AlGaAs

“…The angular separations between GaAs and Al x Ga 1-x As peaks in HRXRD spectra can be determined by substituting in equations (4) to (7) respectively into Braggs equation (8) to yield the peak separation between GaAs and the Al x Ga 1-x As layers which can be expressed, in the case of (004) reflections, as: (8) where θ o and θ x are the Bragg angles associated with GaAs and Al x Ga 1-x As, respectively.…”

“…High resolution x-ray diffraction (HRXRD) is a nondestructive technique requiring no sample preparation that is routinely used to characterize semiconductor materials [8][9][10][11], to determine lattice parameters, layer thicknesses and compositions. The application of the HRXRD technique to the analysis of AlGaAs materials requires the AlAs lattice parameter to be known with high accuracy, however a wide range of values have been reported, between 5.6605 Å and 5.6622 Å [15][16][17][18][19]23].…”

Carbon incorporation in GaAs/Al0.2Ga0.8As triple quantum wells and its effect on laser performance

“…As a common containment, oxygen forms non-radiative centres in GaAs, AlGaAs and GaAs/AlGaAs. Due to the high reactivity of Al (with oxygen), oxygen can be easily incorporated into AlGaAs with a typical density of ≥10 17 cm −3 at an AlAs composition of 30% and increases with increasing composition of AlAs [1,2,9]. In the structures studied, the segregation of oxygen-related non-radiative centres at inverted interfaces of the Al 0.2 Ga 0.8 As/GaAs QWs may be only partially responsible for the broader PL FWHM, as we have deliberately employed low composition of AlAs (20%) in the barrier layers.…”

Long-wavelength infrared quantum-dot based interband photodetectors

“…Nonetheless, under these conditions it is noted that a GaAs dot density comparable to reported molecular beam epitaxy (MBE) results [15,16] can be achieved. Furthermore, an extraordinary high dot density is exhibited by the Al 0.35 Ga 0.65 As sample, possibly a consequence of the stronger Al-As bonds that limit the surface diffusion length and create a high density of nucleation centers for QD formation [17]. On the other hand, the dot density is lower for the GaAs 0.7 Sb 0.3 sample, probably reflecting the lower strain in the system.…”