Metal-clad nitride semiconductor laser diodes

Abstract

An edge-emitting laser diode (LD) is described in which the upper epitaxial cladding layer is replaced with an evaporated metal contact selected for its optical as well as electrical properties. Typical nitride laser diodes have a p-doped epitaxial AlGaN as the upper cladding layer. This conventional upper cladding structure can pose an obstacle to high indium-containing active layers, such as those in green lasers, because the high growth temperature of the cladding layer can degrade the underlying InGaN regions. Moreover, the p-doping of a conventional cladding layer causes significant free-carrier absorption. Our alternative cladding structure offers design flexibilities for reducing optical loss. We demonstrate the novel device structure through an In0.1Ga0.9N multiple-quantum-well laser diode operating at 412 nm with silver (Ag) rather than the typical p-type AlGaN as the upper cladding layer. We further demonstrate that a composite indium-tin-oxide/Ag contact also works as an effective cladding layer. The ITO is deposited by RF sputtering, while Ag is deposited by thermal evaporation. Silver is effective as a cladding layer because of its very low index of refraction at the lasing wavelength, so the guided optical mode exhibits minimal penetration into the silver.