High quality InGaAs/AlGaAs lasers grown on Ge substrates

We demonstrate the feasibility of germanium wafers as a growth substrate fo r most electro-optic devices that are normally grown on GaAs wafers. Ge off ers the advantage of lower cost, higher strength and the potential of large r diameters compared to GaAs substrates. An intermediate GaAs buffer layer accounts for the transition from the nonpolar Ge to the polar GaAs crystal. Material quality on top of the buffer layer is comparable to material grow n directly on GaAs substrates. This is illustrated by CW-operation at 980 n m of lasers grown on Ge, with a threshold current of 19 mA and a differenti al quantum efficiency of 28% per (uncoated) facet for 500 mu m long and 5 m u m wide ridge lasers, compared to values of 14 mA and 30% for lasers grown on GaAs substrates in the same run. Also 850 nm microcavity LEDs on Ge wer e investigated. First results already indicate external quantum efficiencie s of 4.5%. (C) 1998 Elsevier Science B.V. All rights reserved.