(Received November 11, 1995; accepted for publication December 20, 1995)
Subband structures and optical gains of both unstrained and biaxial strained wurtzite GaN/AlGaN quantum well (QW) laser diodes (LDs) are theoretically investigated by the 8×8 k\cdotpp theory, with the assistance of the first-principles calculations in the derivation of the required parameters such as deformation potentials. The strong electron affinity and the small spin-orbit coupling of a nitrogen yield much heavier effective masses even in the QWs. It plays an essential role in causing a higher threshold current density for any well length than GaAs/AlGaAs QW LDs. Considering a biaxial strain induced by the lattice mismatch, the optical gain property qualitatively improves for any well length. However, the effect on the reduction of the threshold current density is quantitatively not so effective as GaAs/AlGaAs QW LDs.