Distributed-feedback blue laser diode utilizing a tunnel junction grown by plasma-assisted molecular beam epitaxy

Area of Science:

• Materials Science
• Optoelectronics
• Semiconductor Physics

Background:

• Gallium Nitride (GaN)-based laser diodes (LDs) are crucial for various optical applications.
• Standard Fabry-Perot (FP) LDs have limitations in spectral purity and mode control.
• Distributed Feedback (DFB) LDs offer improved spectral characteristics but require optimized designs.

Purpose of the Study:

• To demonstrate a novel tunnel junction (TJ) approach for fabricating GaN-based DFB laser diodes (LDs).
• To enhance the coupling coefficient and performance of DFB LDs by optimizing grating placement and optical mode overlap.
• To compare the performance of the novel TJ-based DFB LD with a standard FP LD.

Main Methods:

• Fabrication of GaN-based DFB LDs utilizing a tunnel junction (TJ) structure.
• Integration of the DFB grating directly on top of the ridge, enabled by the TJ.
• Characterization of the DFB LD's optical performance, including operating wavelength and side mode suppression ratio (SMSR).

Main Results:

• The novel TJ approach allows the DFB grating to be placed directly on the ridge, maximizing optical mode overlap.
• A high coupling coefficient is achieved due to the high refractive index contrast between air and GaN.
• The demonstrated DFB LD operates at a wavelength of 450.15 nm with an SMSR exceeding 35 dB.

Conclusions:

• The tunnel junction (TJ) is an effective technique for realizing high-performance GaN-based DFB laser diodes (LDs).
• This novel design significantly improves spectral purity compared to standard Fabry-Perot LDs.
• The demonstrated DFB LD shows promising results for applications requiring narrow spectral linewidth and high SMSR.