Thermal transport of nanoporous gallium nitride for photonic applications

Recently, nanoporous (NP) GaN has emerged as a promising photonic material in the III-N family. Due to its attractive properties, such as its large refractive index contrast and perfect lattice matching with GaN, as well as its good electrical conductivity, photonic components and devices involving NP GaN have been successfully demonstrated. However, further development of high-performance NP GaN based electrically injected devices, such as vertical-cavity surface-emitting lasers (VCSELs) and edge emitting lasers, requires efficient heat dissipation. Therefore, in this paper, we study thermal conductivity (TC) of NP GaN, especially when incorporated into a practical distributed Bragg reflector (DBR) in a VCSEL device. Through an effective medium model, we study the theoretical effect of NP GaN morphological properties over its TC. We then experimentally measure the TC of NP GaN, with different porosities and pore wall thicknesses, which shows a high agreement with the theoretical model. We also fabricate actual NP GaN DBRs and study the large tunability and interdependence among their TC (1-24 W/m K), refractive index (0.1-1.0), and electrical conductivity (100-2000 S/m) compared to other conventional DBRs. Finally, we perform a finite-element simulation of the heat dissipation within NP GaN-VCSELs, revealing their superior thermal dissipation compared to dielectric DBR based VCSELs. In this regard, this study lays the foundation for nanoscale thermal engineering of NP GaN optoelectronic and photonic devices and paves the way for their successful commercialization.