We have proposed a new physical approach for the design of mid-IR lasers based on type II heterojunctions with a large asymmetric band-offset at the interface. These high potential barriers produce effective electron-hole confinement at the interface and results in a tunnel-injection radiative recombination mechanism within the device due to reduced leakage current from the active region. The creation of high barriers for carriers leads to their strong accumulation in the active region and increases quantum emission efficiency of the spatially separated electrons and holes across the heteroboundary. Our approach also leads to the suppression of non-radiative Auger-recombination and a corresponding increase in the operation temperature of the laser. The active region of the laser structure consists of the type II heterojunction formed by narrow-gap InGaAsSb and wide-gap GaInAsSb layers lattice-matched to InAs substrate. In the present work we compare the behaviour of p-p and p-n heterointerface tunnel injection lasers grown by LPE operating at λ=3.2-3.26 μm