High temperature study of GaN UV laser diodes

Laser diodes (LDs) emitting in the short-visible and ultraviolet ranges have received considerable research interest due to their wide range of applications, such as communications, spectroscopy, data storage, and quantum sensing. The III-nitride material system is especially well suited to meet these LD needs due to their wide, direct bandgap, high thermal conductivity, and high electron mobility. By controlling the alloy composition within the quantum wells of a LD device, the material bandgap and thus emission wavelength can be precisely engineered for specific applications. High current densities are needed to achieve sufficient gain to support laser operation and even higher current densities are needed to achieve high output intensity. These substantial current densities lead to significant self-heating during laser operation, which in turn leads to a shift in emission wavelength, an increase in threshold current density, and a decrease in device efficiency. These effects and the stability of LD operation at elevated temperatures can be described through the characteristic temperatures T0, the characteristic temperature of lasing threshold, and T1, the characteristic temperature of differential efficiency. In this work, we use a thermoelectric module (TEC) and pulsed operation to precisely control the temperature of a 20 μm x 1500 μm InGaN/AlGaN LD with a room temperature emission wavelength of 376nm during laser emission. We report a T0 of 192 K and a T1 of 825 K, demonstrating the high degree of stability of this UV-A LD with increasing temperatures.