Reveal the threading dislocation pits of AlGaAs related epitaxial layer by wet oxidation

The native oxides of AlAs and AlGaAs are formed in the way the Al-bearing regions are exposed in a water-vapor ambient at from 400 to 500/spl deg/C. These oxides formed by this reaction are stable, have a low refractive index and good electrical insulation making them extremely useful for electrical and optical confinement. These Al based oxides have been applied to such devices and structures as gain-guided stripe-geometry edge-emitting lasers, index-guided laser arrays, buried-mesa index-guided EEL, ring-cavity lasers, ultra-low threshold vertical cavity lasers. The refractive index of the AlAs native oxides (Al/sub x/O/sub y/) is much lower than AlGaAs itself under visible light wavelength. It´s very easy to distinguish the oxidized area and the un-oxidized area. Here, we report a new method to reveal the threading dislocation density of AlGaAs related epilayers by wet oxidation. During the wet oxidation, the oxygen go inside the material along with the dislocation line and oxidizes the AlGaAs layers to form oxidation cylinder. On the surface, the cross section of such cylinder is a disk. It´s very easy to observe such kind of oxidation disk by optical microscopy because of the large difference of refractive index between the oxidized and un-oxidized AlGaAs.