Molecular beam epitaxial growth of ZnMgSSe and its application to blue and green laser diodes

Abstract

ZnMgSSe alloys lattice‐matched to GaAs substrates have been successfully grown by molecular beam epitaxy. The band gap energy and refractive index at a wavelength of 500 nm for ZnMgSSe at room temperature were given as a function of the lattice‐matching alloy composition of Mg and S. Conductive n‐ and p‐type epitaxial layers were produced using ZnCl₂ and plasma‐excited N₂ as doping sources. The maximum net acceptor concentration attainable in p‐ZnMgSSe decreased below 5×10¹⁶ cm⁻³ as the band gap energy increased above 2.91 eV, which is currently limiting the useful range of ZnMgSSe as a cladding layer in laser diodes. Room temperature continuous‐wave (cw) operation of ZnCdSe/Zn(S)Se/ZnMgSSe single strained quantum well separate confinement heterostructure lasers has been achieved for emission in the range from 490 to 524 nm. More than 0.38 eV energy difference between the band gap of the ZnMgSSe cladding layer and the effective band gap of ZnCdSe strained quantum well was required to obtain cw operation. Employing a ZnTe/ZnSe resonant tunneling superlattice as the p‐type contacting scheme, the threshold voltage of II–VI laser diodes could be reduced to 4.9 V. The device lifetime was significantly dependent on the dislocation density in the II–VI layers.