Role of Quasi-Fermi Levels in Si- and Mg-Related Optical Absorption in Nitride Laser Diodes (LDs): Material Context

Optical absorption and reabsorption of light emitted from the active regions in nitride laser diodes (LDs) reduce the light extraction efficiency of these devices. The presence of Si and Mg can considerably increase optical absorption, an effect that is much stronger in the high-energy (short-wavelength) spectral range. This absorption increase is governed by the ionization of Si donor and Mg acceptor states, which are controlled by the electron and hole quasi-Fermi levels. We demonstrate that absorption increases due to enhanced Mg ionization caused by compensation in the p-type region, alongside high Si ionization in the n-type region. A theoretical explanation is provided for the observed increase in optical efficiency achieved by removing dopants from the waveguides. Furthermore, superior material quality is shown to yield low absorption levels, especially within the Mg-doped p-type region of the device.