Impact of mismatch-related phenomena on a room-temperature operation of nitride VCSELs.

The influence of mismatch-related phenomena (mostly strain fields and structure defects) on a room-temperature (RT) operation of possible nitride VCSELs is examined using a simple but still detailed analytical model. Intentionally introduced stress fields within nitride VCSEL quantum-well (QW) active regions (band-gap engineering) are found to have a much weaker effect on their optical gain than in the case of conventional arsenide and phosphide VCSELs. Dislocation densities (including misfit dislocations), on the other hand, have a considerable harmful impact on VCSELs thresholds, mostly because of increasing scattering losses and decreasing internal quantum efficiency. Single-quantum-well nitride VCSELs are found to be very sensitive to the above impact. A reasonable increase in a number of QWs in multiple-quantum-well VCSELs tremendously improves their performance. In the case of relatively high dislocation densities, bulk double-heterostructure VCSELs may turn out to be the best nitride designs although they may also exhibit too high thresholds to lase at RT.