Tzeng-Tsong Wu

Continuous wave operation of current injected GaN vertical cavity surface emitting lasers at room temperature

We report the demonstration of the continuous wave laser action on GaN-based vertical cavity surface emitting lasers at room temperature. The laser structure consists of a ten-pair Ta2O5/SiO2 distributed Bragg reflector (DBR), a 7λ-thick optical cavity, ten-pairs InGaN/GaN multiquantum wells with an AlGaN electron blocking layer, and a 29-pair AlN/GaN DBR. The laser has a threshold current of about 9.7 mA corresponding to the current density of about 12.4 kA/cm2 and a turn-on voltage about 4.3 V at 300 K. The lasing wavelength was 412 nm with a linewidth of about 0.5 nm. A spontaneous emission coupling efficiency factor of about 5×10−3 and the degree of polarization of about 55% were measured, respectively. The laser beam has a narrow divergence angle of about 8°.

Characteristics of Current-Injected GaN-Based Vertical-Cavity Surface-Emitting Lasers

This paper reviews the fabrication technology and performance characteristics of current-injected GaN-based vertical-cavity surface-emitting lasers (VCSELs) with hybrid distributed Bragg reflectors (DBRs). The GaN-based VCSEL consists of a ten-pair Ta2O5/SiO2 top DBR, a 7 λ-thick optical cavity embedded with 10 InGaN/GaN multiquantum wells, and a 29-pair AlN/GaN bottom DBR. Lasing action is observed under continuous-wave operation at room temperature. The laser characteristics, such as temperature-dependent laser threshold current, emission wavelength, and spontaneous emission coupling factors, have been measured and discussed.

GaN-based high contrast grating surface-emitting lasers

GaN-based high contrast grating surface-emitting lasers (HCG SELs) with AlN/GaN distributed Bragg reflectors were reported. The device exhibited a low threshold pumping energy density of about 0.56 mJ/cm2 and the lasing wavelength was at 393.6 nm with a high degree of polarization of 73% at room temperature. The specific lasing mode and polarization characterisitcs agreed well with the theoretical modeling. The low threshold characteristics of our GaN-based HCG SELs faciliated by the Fano resonance can serve as the best candidate in blue surface emitting laser sources.

Threshold gain analysis in GaN-based photonic crystal surface emitting lasers

We have analyzed threshold gains and lasing modes in GaN-based photonic crystal (PC) surface emitting lasers (PCSELs) by using the multiple scattering method (MSM) for triangular-lattice PC patterns. Moreover, GaN-based PCSELs with different boundary shapes have been fabricated and measured. The lasing mode at the Γ band edge of GaN-based PCSELs can be identified by using the angled resolved spectroscopy and matched well to the results calculated by MSM. Threshold conditions in the GaN-based PCSELs with different boundary shapes are obtained by optical pumping and agree well with simulation results.

Localized Lasing Mode in GaN Quasi-Periodic Nanopillars at Room Temperature

In this paper, GaN quasi-periodic nanopillars were fabricated and investigated. The quasi-periodic nanopillars were realized by nanoimprint technique and selective area growth. Localized lasing mode was identified in the GaN quasi-periodic nanopillars. The threshold energy density and lasing wavelength were 40 mJ/cm2 and 369 nm, respectively. The divergence angle and near-field lasing spot were measured to be 10.5° and 3.6 μm, respectively. The spontaneous emission coupling factor of localized lasing mode was estimated to be 9.4 × 10-3. The mode patterns in the real and reciprocal spaces were calculated by the multiple scattering method to confirm the mode localization behavior.

High quality factor nonpolar GaN photonic crystal nanocavities

High quality factor a-plane nonpolar GaN two-dimensional photonic crystal (PC) nanocavities on r-plane sapphire substrates have been demonstrated. Nonpolar GaN PC nanocavities on a thin membrane structure were realized by using e-beam lithography to define the PC patterns and focused-ion beam milling to fabricate the suspended thin membrane. A dominant resonant mode at 388 nm with a high quality factor of approximately 4300 has been demonstrated at 77 K by the micro-photoluminescence system. Moreover, the degree of polarization of the emission from the non-polar GaN PC nanocavity was measured to be 64% along the m crystalline direction.

Study of Band-Edge Modes in GaN-Based Photonic Crystal Surface-Emitting Lasers by the Multiple-Scattering Method

In this paper, we have investigated the mode patterns in real space and reciprocal space, and threshold gain at different band edges in GaN-based photonic crystal surface-emitting lasers (PCSELs) by using the multiple-scattering method. The characteristics at each band edge (Γ1 , K2, and M3) of PCSELs are simulated and discussed. In addition, GaN-based PCSELs operated at different band edges have been fabricated and measured. The experimental results of threshold show good agreement with the simulation results.

GaN-based photonic crystal surface emitting lasers with central defects

The GaN-based photonic crystal surface emitting lasers (PCSELs) with different central defects were fabricated and investigated. The threshold energy densities increased from 3.23 to 3.51 mJ/cm2 when the central defect size increased. In addition, lasing wavelengths decreased from 400 nm to 390 nm due to the guided mode shifting phenomenon for the PCSEL cavities with larger central defects. The tendency of threshold gain and resonance wavelength for PCSELs with different central defects were calculated by the multiple scattering method and well matched to the experimental results.The GaN-based photonic crystal surface emitting lasers (PCSELs) with different central defects were fabricated and investigated. The threshold energy densities increased from 3.23 to 3.51 mJ/cm2 when the central defect size increased. In addition, lasing wavelengths decreased from 400 nm to 390 nm due to the guided mode shifting phenomenon for the PCSEL cavities with larger central defects. The tendency of threshold gain and resonance wavelength for PCSELs with different central defects were calculated by the multiple scattering method and well matched to the experimental results.

Light Emission Characteristics of Nonpolar a-Plane GaN-Based Photonic Crystal Defect Cavities

In this paper, the light emission performance from nonpolar

Effects of Lattice Types on GaN-Based Photonic Crystal Surface-Emitting Lasers

a