Key Takeaways & Executive Findings
- •• Demonstrated room-temperature electrically injected GaN-based VCSEL using a conductive nanoporous DBR, overcoming the lack of p-type conductive DBRs. • The nanoporous DBR provides both high reflectivity and electrical conductivity, enabling vertical current injection and simplified fabrication. • Achieved continuous-wave lasing at room temperature with low threshold current, showcasing potential for high-density integration. • The approach eliminates the need for complex flip-chip bonding or substrate thinning, improving device yield and thermal management.
Abstract
Vertical-cavity surface-emitting lasers (VCSELs) offer numerous advantages, including the ability to form two-dimensional arrays, low power consumption, and easy coupling, making them promising for visible-light communication, sensing, and micro-display applications. In GaAs-based VCSELs, the structure typically includes n-type and p-type epitaxial semiconductor distributed Bragg reflectors (DBRs) and quantum wells (QWs). Since the DBRs are conductive, vertical current injection is straightforward, supporting high-density integration. However, in GaN-based VCSELs, the lack of p-type conductive epitaxial semiconductor DBRs has led most devices to use either two dielectric DBRs or a p-side dielectric DBR combined with an n-type epitaxial III-nitride DBR. For GaN-based VCSELs with two dielectric DBRs, one approach involves exposing the n-side through complex flip-chip bonding and substrate removal to deposit an insulating dielectric DBR with low thermal conductivity, resulting in high thermal resistance. Another approach adopts a long cavity to reduce thermal resistance by thinning the substrate from about 400 μm down to 20 μm, but the thinning process easily induces cracking, affecting device performance and yield. Thus, the VCSEL structure with a p-side dielectric DBR together with an n-type epitaxial III-nitride DBR is more preferable, offering a simple fabrication process, vertical current injection with an n-side bottom electrode, and the ability for high-density integration of micro projection displays. There are a few reports on conductive epitaxial III-nitride DBRs, such as GaN/AlGaN DBR and GaN/AlInN DBR. Among them, the GaN/AlInN DBR shows good lattice match and has been widely studied. However, according to the literature, the epitaxial Si-doped 10-pair AlInN/GaN DBR shows a high series resistance (~60 Ω) due to a large band offset between AlInN and GaN. To achieve highly reflective AlInN/GaN DBR for VCSEL, it usually requires more than 40 pairs, making vertical current injection almost impossible. On the other hand, the gr...
1. Introduction
Vertical-cavity surface-emitting lasers (VCSELs) have numerous advantages, such as the ability to form two-dimensional arrays, low power consumption, and easy coupling. As a result, they are promising for visible-light communication, sensing, and micro-display applications. In GaAs-based VCSELs, the structure mainly includes n-type and p-type epitaxial semiconductor distributed Bragg reflectors (DBRs) and quantum wells (QWs). Since the DBRs are conductive, the vertical current injection is easy to implement, which supports high-density integration.
However, in GaN-based VCSELs, the p-type conductive epitaxial semiconductor DBR is lacking, most devices reported so far use two dielectric DBRs or a p-side dielectric DBR together with a n-type epitaxial III-nitride DBR. For GaN-based VCSELs with two dielectric DBRs, one approach involves exposing the n-side through complex flip-chip bonding and substrate removal to deposit an insulating dielectric DBR with low thermal conductivity, resulting in high thermal resistance. Another approach adopts a long cavity to reduce the thermal resistance by thinning the substrate from about 400 down to 20 μm, however, the thinning process easily induces cracking, affecting the device performance and yield. Thus, the VCSEL structure with a p-side dielectric DBR together with a n-type epitaxial III-nitride DBR is much more preferable, showing simple fabrication process, vertical current injection with a n-side bottom electrode, and the ability for high-density integration of micro projection displays.
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Chuanjie Li, Meixin Feng, Jianping Liu, Aiqin Tian, Xuan Li, Wei Zhou, Rui Xi, Shuming Zhang, Qian Sun, Hui Yang (2025). Room-temperature electrically injected GaN-based vertical-cavity surface-emitting laser with conductive nanoporous distributed Bragg reflector. SinoTechIntel Verified Research. https://doi.org/10.1088/1674-4926/25120042
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Frequently Asked Questions
What is the main innovation of this GaN-based VCSEL?
The main innovation is the use of a conductive nanoporous distributed Bragg reflector (DBR) that provides both high reflectivity and electrical conductivity, enabling vertical current injection in a GaN-based VCSEL without the need for p-type conductive DBRs.
How does the nanoporous DBR overcome previous limitations?
Previous GaN-based VCSELs relied on dielectric DBRs or complex fabrication processes. The nanoporous DBR offers a simpler fabrication process, eliminates the need for flip-chip bonding or substrate thinning, and provides good thermal management, leading to improved device performance and yield.
What are the potential applications of this technology?
The technology is promising for visible-light communication, sensing, micro-display applications, and high-density integration of micro projection displays.
What is the significance of room-temperature operation?
Room-temperature operation is crucial for practical applications, as it allows the laser to be used without complex cooling systems, making it more viable for commercial deployment.
How does this compare to previous GaN-based VCSELs?
Compared to previous GaN-based VCSELs that used two dielectric DBRs or required substrate thinning, this device offers a simpler structure, lower thermal resistance, and easier vertical current injection, potentially enabling higher performance and integration density.
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