Continuous wave operation of high power GaN-based blue vertical-cavity surface-emitting lasers using epitaxial lateral overgrowth

Techniques to reduce thermal resistance in flip‐chip GaN‐based VCSELs

“…This is due to the heat generated in the active region traveling a shorter lateral distance through the epitaxial layers toward the heat sink for lower alignment tolerances. To estimate the thermal resistance required to achieve CW lasing at RT, previously reported CW GaN‐based VCSELs by Nichia and Sony were simulated with their corresponding material and assuming alignment tolerances of 5 μm for all lithography steps on the schematics reported in the original publications. Nichia utilized two dielectric DBRs and large electrode contacts to a highly thermally conductive silicon substrate, resulting in an estimated thermal resistance of 4169 K W −1 , which falls below the 2.5 μm tolerance plot for our flip‐chip design.…”

“…Using the experimental data provided in Refs. and the thermal resistance values modeled here, one can estimate the internal temperature in the active region at threshold. The temperature rise is given by, where Δ T , Z t , V th , I th , R s , and P out are the internal temperature change, thermal resistance, threshold voltage, threshold current, series resistance, and output power of the VCSEL, respectively.…”

“…Wide‐bandgap GaN‐based optoelectronic devices have attracted significant attention for a variety of commercial applications . One such device is the vertical‐cavity surface‐emitting laser (VCSEL) which has been heavily researched for their potential advantages over their edge‐emitting counterparts. VCSELs have a small active volume that emits normal to the device surface at low threshold currents.…”

“…Additionally, the low conductivity of p‐type GaN‐based materials and the difficulty in achieving conductive p‐type DBRs necessitates the use of an intracavity contact (i.e., current spreading layer) for injecting current into the active region. Although electrically injected CW lasing at room temperature (RT) has been demonstrated for GaN‐based VCSELs ; the output powers of these devices are limited to a few milliwatts by thermal roll‐over at high current densities. The self‐heating in these devices leads to an increase in non‐radiative carrier losses and a misalignment of the peak gain wavelength and the cavity resonance wavelength.…”

Highly-efficient operation and mode control in GaN-based VCSELs with a curved mirror

“…Thus, one longitudinal mode almost matches the location of the peak in the gain spectrum automatically and exploits the maximum amplification. In the case of a short cavity with a wide spacing of more than 10 nm, the length should be precisely controlled to ensure the longitudinal modes hit the top of the gain spectrum [20]. This frequently results in a fabrication error, which can deteriorate the lasing yield.…”