Long-wavelength VCSELs with buried tunnel junction

Despite the earliest work on VCSELs in the late 1970s on InP-based materials, the further realization of VCSELs beyond 1.3 emission wavelength has been significantly delayed for many years with respect to their short-wavelength counterparts on GaAs substrates. This chapter covers the specific challenges, solutions and application prospects of VCSELs in non-GaAs-based material systems which are suitable for achieving significantly extended wavelength ranges. By using highly advanced device concepts, since the late 1990s it became possible to overcome the fundamental technological drawbacks related with long-wavelength VCSELs such as inferior thermal properties and to realize lasers with remarkable device performance. In particular and with respect to huge application opportunities in optical communications, this chapter presents InP-based VCSELs with single-mode output powers of several milliwatts at room temperature and well beyond 1 mW at as well as modulation frequencies far above 10 GHz in conjunction with ultra-small power consumption. While the InP-based VCSEL technology is limited to maximum emission wavelengths around 2.3 even longer emission up to the mid-infrared wavelength range can be achieved with VCSELs based on GaSb. With their inherent and, compared to other laser types, superior properties like enhanced tuning characteristics, long-wavelength VCSELs are regarded as key components for applications in optical sensing.