Another potential difficulty is that the bandgap of lattice matched InGaAs is very close to the desired 1.55 m wavelength range. As alloys which are lattice matched to InP across a large wavelength range. The introduction of these alloys will further increase the flexibility of this material system and allow graded heterojunctions to be introduced. Ge also has very low recombination rates and the desired moderate absorption coefficient above 1 m. However, the lack of an intermediate bandgap alloy would lead to charge trapping at the heterojunctions.
Some difficulties arise when outstanding material quality is required.
It is very difficult to control the carrier concentration in either semiconductor material near a heterojunction because of autodoping caused by interdiffusion. Thus, a workable detector must be designed as shown in Fig. 15 . The growth of such a structure requires two separate deposition systems for Ge and the arsenides. Ge contact region. Furthermore, the resonant modes of the optical cavity can be tuned by varying the thickness of the GaAs contact layer before Ge growth.