Role of quasi-Fermi levels in Si- and Mg-related optical absorption in nitride laser diodes (LDs): material context

TL;DR

This paper investigates how quasi-Fermi levels influence optical absorption in nitride laser diodes, highlighting the roles of Si and Mg dopants and the importance of material quality for efficiency.

Contribution

It provides a theoretical and experimental analysis of how doping and quasi-Fermi levels affect optical absorption in nitride LDs, suggesting ways to improve device efficiency.

Findings

Higher ionization of Mg and Si increases absorption in specific spectral ranges.

Removing doping in waveguides reduces optical absorption.

Good material quality correlates with lower absorption levels.

Abstract

Optical absorption and reabsorption of light emitted from active regions in nitride laser diodes (LDs) have been shown to reduce the light extraction efficiency of these devices. It was proven that the presence of Si and Mg may considerably increase the optical absorption. This effect is much stronger in the high-energy (short-wavelength) range of the spectrum. The absorption increase is directly related to the ionization of the Si donor and Mg acceptor levels, which are controlled by the electron and hole quasi-Fermi levels. It is shown that the absorption may be increased because of the higher ionization of Mg caused by the compensation in the p-type region and the high ionization of Si in the n-type region. It was explained theoretically why optical efficiency is increased by removal of doping in waveguides. It was also shown that good material quality leads to a low absorption level, especially in the Mg-doped p-type part of the device.