TEM characterization of oxidized AlGaAs/AlAs nonlinear optical waveguides

Abstract

The internal interfaces of multilayer Al x Ga 1-x As/AlAs nonlinear optical waveguides are investigated by high-angle annular-dark-field and energy-filtered scanning transmission electron microscopy, before and after partial wet oxidation of AlAs layers. Via a simple phenomenological model, the corresponding roughness parameters allow predicting the scattering-induced waveguide optical losses, which are in reasonable agreement with the experimental value of 0.5 cm -1 . We also find that Al x Ga 1-x As layers adjacent to oxidized AlAs tend to be oxidized through the interfaces, even for low Al fraction, with typical oxidation depths of 9 nm for x=0.7 and 2 nm for x=0.

Toward an AlGaAs/AlOx near-infrared integrated optical parametric oscillator

“…Such defects may arise from trapped oxidation reaction products resulting in an excess of elemental arsenic As 0 at the oxide-semiconductor interfaces. Much As Ga would then be generated after the diffusion of As 0 into the neighboring semiconductor layers [30], consistently with the TEM observations recalled at the beginning of this section [14].…”

“…Thanks to a transmission electron microscopy (TEM) characterization of oxidized layers, carried out to assess the chemical and morphological properties of AlOx at the microscopic scale, it has been established that the oxidation process is responsible for the deterioration of the interfaces between layers [14]. In particular, -AlOx layers are composed of γ-Al 2 O 3 polycrystalline grains, sized between 10 and 20 nm, embedded in an amorphous Al x O y matrix, -The roughness at AlGaAs/AlOx interfaces is increased by about 40% and 80% for GaAs and Al 0.7 Ga 0.3 As, respectively, -Residual oxidation of the neighboring GaAs and Al 0.7 Ga 0.3 As layers occurs through the interfaces over 3 and 9 nm, respectively, -Further in the GaAs layers surrounding the AlOx, the material becomes amorphous in the vicinity of the oxidized layers (∼20 nm from the interface) and remains monocrystalline beyond.…”

“…In our case, for each type of interface within the waveguide, the corresponding autocorrelation function has been extracted from the TEM analysis mentioned above, and fitted with a Gaussian function [14]. The interfaces' roughness is therefore described by two statistical parameters: their root-mean-square deviation from the flat surface σ, and their correlation length L C .…”

Near-infrared OPO in an AlGaAs/AlOx waveguide

“…Such defects might arise from trapped oxidation reaction products resulting in an excess of elemental arsenic As 0 at the oxide-semiconductor interfaces. Many As Ga would then be generated after the diffusion of As 0 into the neighboring semiconductor layers [30], consistently with the TEM observations recalled above [26].…”

“…The characterization of oxidized layers via transmission electron microscopy (TEM) [26], which was carried out to assess the chemical and morphological properties of AlOx at microscopic scale, has established that: -The roughness at AlGaAs/AlOx interfaces is increased by about 40% and 80% for GaAs and Al 0.7 Ga 0.3 As respectively, -Residual oxidation of the neighboring GaAs and Al 0.7 Ga 0.3 As layers occurs through the interfaces over 3 and 9 nm respectively, -Further in the GaAs layers surrounding the AlOx, the material becomes amorphous in the vicinity of the oxidized layers (~20 nm from the interface) and remains mono-crystalline beyond.…”