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UBC Theses and Dissertations

Lateral wet oxidation of AIGaAs and its applications in high index contrast distributed feedback ridge waveguides Chen, Peng


A high temperature wet oxidation technique has been developed to laterally oxidize high aluminum content Al[sub x]Ga[sub 1-x]As (x=98%) sandwiched between GaAs and low aluminum content Al[sub x]Ga[sub 1-x]As (x=70%). The oxides can be used to produce optical confinement and the current confinement in optoelectronic devices. To characterize the products of this high temperature oxidation, atomic force microscopy has been use to study the induced structure change. No significant vertical expansion has been detected demonstrating that this technique is particularly useful for distributed reflector devices. The composition of the oxidation product was also studied by x-ray photoelectron spectroscopy revealing that the high temperature oxidation produces arsenic poor A10[sub x]. We explained that the As is lost by thermal evaporation of AsH₃ during the high temperature oxidation process. By studying the binding energy of Al 2p core levels in the oxide, it has been found that the high aluminum content Al[sub x]Ga[sub 1-x]As (x=98%) oxidizes to an A10[sub x] while the low aluminum Al[sub x]Ga[sub 1-x]As (x=70%) produces Al₂O₃. To apply the lateral oxidation to distributed feedback waveguides, we used electron beam lithography and wet etching to fabricate test waveguides. By optimizing the process parameters, 100 nm linewidth gratings with spacing greater than 280nm have been achieved. A multipass writing technique was developed to attenuate the electron beam writing noise and achieve superior uniformity. The surface grating ridge waveguides have been fabricated on the laterally oxidized Al[sub x]Ga[sub 1-x] As layer successfully. Optical diffraction measurements have been conducted on second-order distributed-feedback waveguides containing a buried oxide with the grating pitch from 300 nm to 500 nm. The dispersion relationships of photon energy versus propagation constant have been determined for 440 nm and 460 nm grating waveguides. The experiments give the effective indices of the waveguides to be 1.7 for the both fundemental TE modes and fundemental TM modes, which show the guided modes were strongly modulated by the buried oxide.

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