The effects of magnesium doping on the modal loss in AlGaN-based deep UV lasers

Abstract

Absorption losses in the Mg-doped layers significantly contribute to the modal losses in group-III-nitride-based lasers. In this paper, we investigate the influence of Mg-doping on the modal absorption of optically pumped UVC lasers grown on epitaxially laterally overgrown AlN/sapphire substrates with an averaged threading dislocation density of 1 × 109 cm–2. By varying the setback of the Mg-doping (∼1 × 1020 cm−3) within the upper Al0.70Ga0.30N waveguide layer, the overlap of the optical mode with the Mg-doped region increases. For all structures, internal losses were derived from gain spectra obtained by the variable stripe length method. The internal losses increase from 10 cm−1 for lasers without Mg-doping to 28 cm−1 for lasers with a fully Mg-doped upper waveguide layer. The overlap of the optical mode with the Mg-doped waveguide ΓMg clearly correlates with the modal losses. This allows to calculate the Mg-induced losses in current injection laser diodes by αmodMg=ΓMg×50 cm−1.

Room-temperature operation of AlGaN ultraviolet-B laser diode at 298 nm on lattice-relaxed Al0.6Ga0.4N/AlN/sapphire

“…The AlN molar fractions of the n-Al 0.6 Ga 0.4 N and u-Al 0.45 Ga 0.55 N guide layers were confirmed by X-ray diffraction and reciprocal space mapping imaging around (20)(21)(22)(23)(24) diffraction. The n-Al 0.6 Ga 0.4 N was almost 100% lattice-relaxed from the underlying AlN.…”

“…First graded u-Al 0.9→0.45 Ga 0.1→0.55 N, undoped, was used for light confinement within the guide layers, preventing internal loss caused by the absorption by the Mg impurity. 23,24) 2nd graded p-Al 0.45→0 Ga 0.55→1 N and p-GaN contact were used for current injection in 1st graded u-Al 0.9→0.45 Ga 0.1→0.55 N from the p-electrode. Mesa structure was formed using inductively coupled plasma etching, with chlorine as the etching source to expose the n-Al 0.6 Ga 0.4 N surface.…”

Transverse Electric Lasing at a Record Short Wavelength 244.63 nm from GaN Quantum Wells with Weak Exciton Localization

“…Deep ultraviolet (DUV) lasers based on the AlGaN quantum well (QWs) have been extensively investigated for their critical applications in covert communication, spectral analysis, optical storage, medical diagnostics, and so on. − The current injected AlGaN QW DUV laser at 271.8 nm has been developed on the bulk AlN substrate . In addition, the optically pumped AlGaN QW lasers have reached down to 237 nm. − However, due to the valence sub-bands crossover of AlGaN, the optical polarization of DUV lasers switches from the transverse electric (TE) mode to the transverse magnetic (TM) mode when the emission wavelengths were shorter than 238 and 249 nm on less available AlN and more available sapphire substrates, respectively. , The switch of the optical polarization to TM could compromise the laser performance as the TM mode suffers from lower facet reflectivity and could be more easily absorbed by the p-type layers and metals due to wider optical modes. , Another caveat of the AlGaN QWs is the quantum confined Stark effect (QCSE) that occurs in the several nm thick AlGaN QW.…”

Influence of Electron Blocking Layer on Properties of InGaN-Based Laser Diodes Grown by Plasma-Assisted Molecular Beam Epitaxy

“…In the first set, the Mg doping levels were changed (0.7, 1.5, 3, 6) × 10 19 cm −3 for a 20 nm thick EBL. In the second set, the doping level was constant at 1.5 × 10 19 cm −3 and the thickness was changed, i.e., (5,10,20) nm. More details on growth and processing of the devices can be found in [17].…”

“…Nowadays, state of the art LDs have α i = 1 cm −1 and the maximum optical power is 7.2 W [4]. It was shown that, in the case of InGaN-based LDs, the high α i originates from light absorption in the Mg-doped layers [5][6][7][8][9][10][11].…”