Tsung-Ting Kao

GaN-based two-dimensional surface-emitting photonic crystal lasers with AlN∕GaN distributed Bragg reflector

GaN-based two-dimensional (2D) surface-emitting photonic crystal (PC) lasers with AlN∕GaN distributed Bragg reflectors are fabricated and demonstrated. The lasing threshold energy density is about 3.5mJ∕cm2 per pulse under optical pumping at room temperature. Only one dominant emission wavelength of 424.3nm with a narrow linewidth of 1.1A above the threshold is observed. The laser emission covers whole circularly 2D PC patterns (50μm in diameter) with a small divergence angle. The lasing wavelength emitted from 2D PC lasers with different lattice constants occurs at the calculated band-edges provided by the PC patterns. The characteristics of large area, small divergence angle, and single mode emission from the GaN-based 2D surface-emitting PC lasers should be promising in high power blue-violet emitter applications.

Optically Pumped GaN-based Vertical Cavity Surface Emitting Lasers: Technology and Characteristics

We review the fabrication technology and performance characteristics of optically pumped GaN-based vertical cavity surface emitting lasers (VCSELs). Two types of VCSELs with different microcavity structures are described. First type of VCSEL has a hybrid microcavity structure that consists of an epitaxially grown AlN/GaN distributed Bragg reflector (DBR), a GaN active layer with InGaN/GaN multiple quantum wells (MQWs), and a Ta2O5/SiO2 dielectric DBR. Second type of VCSEL has a dielectric DBR microcavity structure that has a similar InGaN/GaN MQWs active layer sandwiched in two dielectric DBRs formed by Ta2O5/SiO2 and TiO2/SiO2. Both types of VCSELs achieved laser action under optical pumping at room temperature with emission wavelength of 448 and 414 nm for hybrid DBR VCSEL and dielectric DBR VCSEL, respectively. Both lasers showed narrow emission linewidth with high degree of polarization and large spontaneous emission coupling factors of about 10-2. In addition, a high characteristic temperature of over 240 K was measured, and a distinct spatially inhomogeneous emission pattern was observed.

Characteristics of GaN-based photonic crystal surface emitting lasers

Characteristics of GaN-based photonic crystal surface emitting lasers (PCSELs) were investigated and analyzed. The GaN-based PCSEL emits a blue wavelength at 401.8 nm with a linewidth of 1.6 A and shows a threshold energy density about 2.7 mJ/cm2 under the optical pumping at room temperature. The lasing wavelength emitted from PCSELs with different lattice constants occurs at the calculated band edges showing different polarization angles due to the light diffracted in specific directions, corresponding exactly to Γ, K, and M directions in the K-space. Furthermore, the PCSEL also shows a spontaneous emission coupling efficiency β of about 5×10−3 and a characteristic temperature of 148 K.

GaN-Based High-

We report a fabrication and demonstration of a GaN-based high-Q vertical-cavity light-emitting diode (VCLED). The GaN VCLED is composed of a 25-pair high-reflectivity (98%) GaN/AlN distributed Bragg reflector (DBR), an eight-pair SiO2/Ta2O5 dielectric DBR (99%), and a three-lambda optical thickness InGaN/GaN active region. It shows a very narrow linewidth of 0.52 nm, corresponding to a cavity Q -value of 895 at a driving current of 10 mA and a dominant emission peak wavelength at 465.3 nm. In addition, this VCLED emission linewidth continues to decrease with an increasing injection current, suggesting a possible realization of GaN-based vertical-cavity surface emitting lasers.

Q

We demonstrated CW laser operation of GaN-based VCSELs under current injection at 77 K. CW laser action was achieved at a threshold current of 1.4 mA, emitting at 462 nm with a narrow linewidth of about 0.15 nm.

Vertical-Cavity Light-Emitting Diodes

GaN-based photonic crystal surface-emitting lasers(PCSELs) with AlN/GaN distributed Bragg reflectors were fabricated and analyzed. Different lasing characteristics of GaN-based PCSEL has been determeined and demonstrated by the PC lattice constants. The laser emission behavior covered the whole PC patterns of 50 μm in diameter. Under the optical pumping at room temperature, the PCSEL with PC lattice constant of 230nm shows a threshold energy density of about 2.7 mJ/cm2. Above the threshold, one dominated peak emits at 420.11 nm with a linewidth of 1.1 Å. The lasing wavelength emitted from PC lasers with different lattice constants occurs at the calculated band-edges provided by the PC patterns which further shows different polarization angles due to the light diffracted in specific directions, corresponding exactly to Γ, K, and M directions in the K-space. The PCSEL also shows a characteristic temperature of 148K and a spontaneous emission coupling efficiency β of about 5x10-3. Besides, the coupled-wave model in the PC hexagonal-lattice is applied to distinguish the discrepancy in threshold power and the corresponding coupling coefficient. The results show the lasing actions within Γ, K, and M modes have the substantial relation between the threshold energy density and the coupling coefficient.

CW lasing of current injection blue GaN-based vertical cavity surface emitting lasers

We successfully demonstrated and analyzed the characteristics of GaN-based photonic-crystal surface emitting lasers at room temperature at different band edges (Г, K, and M), showing specific thresholds and polarization angles.

The lasing characteristics of GaN-based two-dimensional photonic crystal surface-emitting lasers

Two types of GaN-based blue surface emitting lasers recently developed were presented. One was a vertical cavity surface emitting laser which achieved laser action under CW current injection at 77K. Another is a photonic crystal surface emitting laser operated at room temperature. Detailed fabrication techniques and performance characteristics are described.

Lasing characteristics of GaN-based photonic crystal surface-emitting lasers

In the paper, we describe the fabrication and performance characteristics of GaN-based vertical-cavity surface-emitting lasers (VCSELs) by optical pumping and current injection. According to the employment of high-quality and high-reflectivity AlN/GaN DBRs in the whole structure, the lasing action of optically pumped GaN-based VCSELs with hybrid mirrors has been observed at room temperature. Due to the excellent results of optically pumped GaN-based VCSELs with hybrid mirrors, we further demonstrated the lasing behavior of GaN-based VCSELs by continuous-wave current injection at 77 K. The laser has one dominated blue wavelength located at 462 nm with a linewidth of about 0.15 nm and the threshold injection current at 1.4 mA. The divergence angle and polarization ratio of the GaN-based VCSELs with hybrid mirrors are about 11.7° and 80%, respectively. A larger spontaneous coupling efficiency of about 7.5×10-2 was also measured.

GaN-based blue vertical cavity and photonic crystal surface emitting laser

We demonstrated GaN-based two-dimensional photonic crystal surface emitting lasers with a low threshold pumping energy density of about 2.7 mJ/cm2 and a large spontaneous coupling factor of 5times10-3, and lasing actions from three different band-edges.