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Detailed threshold analysis of UV-emitting nitride vertical-cavity surface-emitting lasers

In the present paper a detailed (but simple from a mathematical point of view) threshold analysis of room-temperature pulse operation of ultraviolet light (UV) emitting GaN/AlGaN/AlN vertical-cavity electrically pumped surface-emitting lasers (VCSELs) is carried out to examine the possible use of this semiconductor injection laser configuration in future mass application. Several VCSEL structures are considered. An index-guided nitride single quantum well (SQW) VCSEL structure ensures the best laser performance, as expected, particularly in the case of small-size devices. But surprisingly, gain-guided SQW VCSELs are found to exhibit comparable thresholds with much simpler double-heterostructure (DH) VCSELs of bulk active regions. Moreover, thresholds of DH nitride VCSELs are proved to be much less sensitive to all optical losses (for example material absorption as well as diffraction, scattering, and end losses) than their SQW counterparts. Therefore the SQW VCSELs need more advanced technology (making possible achievement of lower dislocation densities and/or higher facet reflectivities) to be superior to DH ones.