Low-threshold AlGaN-based UVB VCSELs enabled by post-growth cavity detuning
Giulia Cardinali, Filip Hjort, Nando Prokop, Johannes Enslin, Munise Cobet, Michael A. Bergmann, Johan Gustavsson, Joachim Ciers, Ines Häusler, Tim Kolbe, Tim Wernicke, Åsa Haglund, Michael Kneissl
Abstract
The performance of vertical-cavity surface-emitting lasers (VCSELs) is strongly dependent on the spectral detuning between the gain peak and the resonance wavelength. Here, we use angle-resolved photoluminescence spectroscopy to investigate the emission properties of AlGaN-based VCSELs emitting in the ultraviolet-B spectral range with different detuning between the photoluminescence peak of the quantum-wells and the resonance wavelength. Accurate setting of the cavity length, and thereby the resonance wavelength, is accomplished by using doping-selective electrochemical etching of AlGaN sacrificial layers for substrate removal combined with deposition of dielectric spacer layers. By matching the resonance wavelength to the quantum-wells photoluminescence peak, a threshold power density of 0.4 MW/cm2 was achieved, and this was possible only for smooth etched surfaces with a root mean square roughness below 2 nm. These results demonstrate the importance of accurate cavity length control and surface smoothness to achieve low-threshold AlGaN-based ultraviolet VCSELs.