Influence of low-temperature buffer layers on the optical waveguiding properties of AlxGa1-xN alloys

The influence of buffer layers on the optical waveguide properties of nitri de related semiconductors films grown on sapphire by metalorganic vapor pha se epitaxy has been investigated. Using the prism coupling technique, we me asured the ordinary (n(TE)) and extraordinary (n(TM)) refractive indices of AlxGa1-xN/AlN and AlxGa1-xN/GaN heterostructures, where AlN, GaN are low t emperature buffer layers. We investigated the relationship between the refr active indices of AlxGa1-xN alloys and the Al content (x) at a wavelength o f 632.8 nm: n(TE)=2.3240-0.33x. This investigation demonstrates optical wav eguiding in gallium nitride materials. It is shown that the indices of thic k AlxGa1-xN films are independent of the buffer layer (AlN, GaN). However, the optical propagation losses are highly sensitive to the crystalline qual ity of the layers, particularly to the density of dislocations in the film. The best optical result of 1.2 dB/cm is obtained when the GaN buffer layer was employed, in comparison to 1.8 dB/cm with the AlN buffer layer. We int erpret these results in relation with the transmission electron microscopy analysis. (C) 2001 American Institute of Physics.