Vertical-cavity surface-emitting lasers (VCSELs) are known to have advantages of lower threshold current operation, circular and low-divergence output beam, and lower temperature sensitivity compared to edge-emitting laser diodes. In conventional VCSELs, the formation of a current aperture plays a vital role in the device characteristics. Low laser thresholds and single-transverse-mode operation would not be possible without a well-defined current aperture to confine carriers to generate photons between the two distributed Bragg reflectors. Since the introduction of the controlled oxidation process for the AlxGa1-xAs material system by Dallesasse and Holonyak in 1989, most VCSELs have employed oxidation for current aperture formation as well as optical confinement and this technique has become one of the most commonly used fabrication techniques for traditional III-V compound semiconductor infrared VCSELs. However, for III-N emitters operating at wavelengths in the ultraviolet to green wavelength range, the formation of Al-based native oxide layers has not proven feasible. As a result, various current-confinement techniques have been studied such as, selective-area growth of buried AlN, oxidizing AlInN, and selective activation of acceptors.
In this work, we report an ion-implantation process which is effective for carrier confinement and defines a current aperture for our III-N ultraviolet microcavity light-emitting diodes (MCLEDs). The devices have peak emission wavelength of ~371.4 nm with the spectral linewidth of 5.1 nm at the highest pulsed current injection level of 15 kA/cm2. Further discussion on the material growth, material characterization, implantation parameters, as well as numerical simulation for structural design will be presented in the conference.
We report our current development progress of ultraviolet vertical-cavity surface-emitting lasers, which included the development of an electrically conducting n-DBR consisting of 40-pairs of Si-doped quarter-wavelength layers of Al0.12Ga0.88N and GaN. A peak reflectivity of 91.6% at 368 nm was measured and a series resistance of 17.7Ω was extracted near the maximum measured current of 100 mA. Furthermore, a micro-cavity light emitting diode was demonstrated by utilizing the established n-DBR. A 2λ cavity was subsequently grown on the 40-pair Al0.12Ga0.88N/GaN n-DBR and a peak wavelength of 371.4 nm was observed with spectral linewidth of 5.8 nm.
A 245.3 nm deep ultraviolet optically pumped AlGaN based multiple-quantum-well laser operating at room temperature is described. Epitaxial growth was performed by metalorganic chemical vapor deposition on a c-plane bulk AlN substrate at a growth temperature of ~ 1130 °C. The wafer was fabricated into cleaved bars with a cavity length of ~1.45 mm and the lasing threshold was determined to be 297 kW/cm2 under pulsed 193 nm ArF excimer laser excitation. A further ~20% reduction in threshold pumping power density was observed with six pairs of SiO2/HfO2 distributed Bragg reflector deposited at the rear side of facets.
Data are presented for AlGaN-AlN multiple-quantum-well optically pumped lasers operating at 300K. The structures were grown by MOCVD on bulk AlN substrates and were fabricated into cleaved bars with a cavity length ~1mm. The epitaxial structures consist of ten 3 nm AlGaN quantum wells with 5 nm AlGaN barriers and an AlN buffer layer deposited on a (0001) AlN substrate at a growth temperature 1155 ºC. The bars were photopumped under pulsed conditions at 300K with a 193nm excimer laser. The threshold optical pump power is 455 kW/cm2 and laser emission is observed at 247 nm.
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.
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.
Characteristics of GaN-based photonic crystal surface-emitting lasers (PCSELs) were investigated and analyzed. We
demonstrated two different lattice constant of the GaN-based PCSEL. One with lattice constant of 290nm emits a blue
wavelength at 401.8 nm with a linewidth of 1.6 Angstrom and shows a threshold energy density about 2.7 mJ/cm2 under the
optical pumping at room temperature. The other with lattice constant of 234nm observed a wavelength at 423.8nm
with a linewidth of 1.1 Angstrom and energy density about 3.5 mJ/cm2. The laser emission covers whole circularly 2D PC
patterns (50 µm 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. 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 5x10-3 and a characteristic temperature of 148K.
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