Heterojunction is the term for a region where two different materials interact. A Heterostructure is a combination of two or more materials. Here, we will explore several interesting cases.
The AlGaAs-InGaAs interaction is interesting due to the difference in energy bandgap levels. It was found that AlGaAs has a higher bandgap level, while InGaAs has a lower bandgap. By layering these two materials together with a stark difference in bandgap levels, the two materials make for an interesting demonstration of a heterostructure.
The layering of a smaller bandgap material between a wider bandgap material has an effect of trapping both electrons and holes. As shown on the right side of the below picture, the center region, made of AlGaAs exibits high concentrations of both electrons and holes. This leads to a higher rate of carrier recombination, which can generate photons.
Here, the lasing profile of the material under bias:
A commonly used group of materials is InGaAsP, InGaAs and InP. Unlike the above arrangements, these materials may be lattice-matched. Lattice-matching may be explored in depth later on.Simulations suggest low or non-existent recombination rates. Although this is a heterostructure, one can see that there are no jagged or sudden drastic movements in the conduction and valence band layers with respect to each other to create a discontinuity that may result in a high recombination rate.