Effects of Multiple Oxide Layers in Multi-Junction VCSELs Under Different Pulse Conditions

This report investigates 940 nm vertical-cavity surface-emitting lasers (VCSELs) with three-junction (3J) designs under various pulsed driving conditions, focusing on the influence of oxide layer configurations on electrical and optical performance. Heat accumulation is a critical issue in VCSEL operation; therefore, reducing pulse width effectively minimizes heat generation. This not only enhances the thermal characteristics of the devices but also suppresses lateral carrier diffusion—particularly important in longer resonant cavity structures such as multi-junction VCSELs. At room temperature, a 3J 940 nm VCSEL with a $10\mu $ m oxide aperture driven by 2 ns pulses achieved a slope efficiency (SE) of 3.2 W/A using a three-layer oxide structure, compared to 2.37 W/A for a single-layer oxide design. Both devices exhibited a red spectral shift of less than 1 nm, corresponding to a temperature rise below $12~^{\circ }$ C, indicating improved thermal management. Notably, a unique behavior was observed in the three-oxide-layer 3J VCSEL: as the injection current increased, the beam divergence angle decreased from 17° to 5°. These findings highlight the advantages of multi-junction VCSELs with optimized oxide designs, demonstrating their potential for future high-performance sensing applications.