High aluminum (Al) content AlxGa1-xAs is known to be controllably oxidizable under elevated temperature in the presence of water vapor. Oxidized AlxGa1-xAs exhibits properties that make it desirable for device applications, such as being highly selective on aluminum composition, being electrically insulating, and having a low refractive index. Such characteristics make AlOx a desirable material choice for making efficient grating structures.
We proposed a novel buried AlOx/semiconductor horizontal cavity grating structure. Defect-free high Al content AlxGa1-xAs grown on nonplanar substrates with 0.9 < x < 1 was achieved using low-pressure MOCVD . After oxidation, we obtained a saw-tooth pattern oxide front with a period half of the original lithography defined pitch. An RCE (resonant cavity enhanced) photodetector structure was designed and fabricated using this AlOx grating as its DBR mirrors. This structure can find applications for making microcavity single-wavelength lasers and optoelectronic devices.
Figure 1: SEM cross-sectional views of four different samples, each with four pairs of GaAs/AlGaAs. Darker regions are AlGaAs layers. Samples (a) and (b) have trenches along [01-1] directions, but were grown at two different temperatures, 600°C for (a) and 640°C for (b). The thickness enhancement ratios between the sidewall and the planar region for samples (a), (b), and (d) are 2.20, 1.32, and 1.17, respectively. Sample (c) shows the convergence of two sidewalls. Sample (d) has the trench aligned along  direction. The no-growth plane (111)B is circled in (d), too. The nominal aluminum for all these samples is 0.92.
Figure 2: Oxide front pattern of AlxGa1-xAs on nonplanar substrates with trenches aligned in the [01-1] direction. (a) A schematic shows the nonplanar substrate . (b) Oxide front pattern bright field image. (c) Oxide front pattern top view from the SEM with the backscattered detector.