Theory of optical gain in ideal GaN heterostructure lasers

We present gain calculations for ideal bulk GaN and 100 A GaN quantum well laser structures. We show that due to the large electron and hole effective masses in GaN, the room‐temperature material gain characteristics of a 100 A quantum well are a little different from those of bulk GaN up to a gain level of 1000 cm−1, and that the transparency and threshold carrier density is approximately 2.5 times that in an equivalent GaAs structure, with the radiative current density being of order eight times larger. Comparing the unstrained zinc blende and wurtzite crystal structures, we predict improved gain characteristics in the wurtzite case. The introduction of compressive strain, e.g., through pseudomorphic growth between unstrained AlGaN barriers, will benefit both crystal structures, with wurtzite remaining better than zinc blende for mismatch up to about 1.5%. Finally, we note that the gain characteristics would be further improved if it were possible to grow tensile‐strained zinc blende layers.