  The transmission properties of three-dimensional (3D) massive Kane fermions
in HgCdTe (MCT) heterojunctions have been studied using the simplified
Kane-Mel\'e model. Based on our theoretical calculations, we propose the design
of an electronic device, called mass inverter, which consists of the junction
of a narrow-gap semiconductor and semimetal. Such a device can be used in
electron optics applications, since it operates as a Veselago lens and presents
Klein tunneling (KT) of 3D massive Kane fermions under normal incidence. We
found that KT and Veselago lensing can also be observed for general MCT
heterojunctions with a specific value of doping level. We show that
non-resontant perfect transmission of massive Kane fermions persists in a
potential barrier for heterojunctions formed by a semimetal between two
standard semiconductors. This effect is quite robust when the ideal conditions
of a possible experimental test are deviated. Our findings may have important
implications in the development of nano-electronic devices using 3D massive
Kane fermions, where transmission features of massless particles are recovered.
