Growth of novel broadband high reflection mirrors by molecular beam epitaxy

Novel broadband (Ga,Al)As/CaF2 Bragg mirrors have been grown on Si(1 1 1) s ubstrates for the first time providing large reflectance bandwidth due to a high ratio of refractive indices. Two types of interface morphology have b een observed: a rough one when growing (Ga,Al)As on CaF2 and a smooth one w hen growing CaF2 on (Ga,Al)As. The effect of surface flattening due to CaF2 overgrowth of (Ga,Al)As prevented the accumulation of interface roughness and provided a smoother surface of the top layer compared to that obtained from (1 0 0) oriented growth. Specular highly reflecting surfaces have been obtained showing no cracks. An absolute reflectance as high as 98% have be en determined for a four pair Bragg mirror. (C) 1999 Elsevier Science B.V. All rights reserved.