InGaN multiple quantum wells (MQWs) with green light emission have been grown on GaN stripes oriented
along the [11-20] direction by selective metal-organic vapor phase epitaxy (MOVPE). Several different
window widths were designed in the SiO2 mask. Completed pyramidal InGaN stripes with flat and smooth
{1-101} sidewall were produced on 2-μm windows while trapezoidal stripes with both {1-101} sidewall and
(0001) top surface were obtained on the 5-μm windows. The former has uniform CL emissions at 500 nm on
the {1-101} sidewall and at 550 nm on the narrow ridge. The latter exhibits similar CL emissions at 500 nm
on the sidewall and at 570 nm on the top surface. These wavelength shifts relative to the CL spectrum peak
(450 nm) from the reference region are attributed to thickness enhancement and indium enrichment in
selective MOVPE. The short-wavelength shoulder near 500 nm in the spectrum from the ridge of the
completed pyramidal strip is attributed to overlapping excitation of the sidewall by the SEM incident beam.
The narrow stripe selective growth of the InGaAlAs bulk waveguides and InGaAlAs MQW waveguides was first investigated. Flat and clear interfaces were obtained for the selectively grown InGaAlAs waveguides under optimized growth conditions. These selectively grown InGaAlAs waveguides were covered by specific InP layers, which can keep the waveguides from being oxidized during the fabrication of devices. PL peak wavelength shifts of 70 nm for the InGaAlAs bulk waveguides and 73 nm for the InGaAlAs MQW waveguides were obtained with a small mask stripe width varying from 0 to 40 μm, and were interpreted in considering both the migration effect from the masked region (MMR) and the lateral vapor diffusion effect (LVD). The quality of the selectively grown InGaAlAs MQW waveguides was confirmed by the PL peak intensity and the PL FWHM. Using the narrow stripe selectively grown InGaAlAs MQW waveguides, then the buried heterostructure (BH) lasers were fabricated by a developed unselective regrowth method, instead of conventional selective regrowth. The InGaAlAs MQW BH lasers exhibit good performance characteristics, with a high internal differential quantum efficiency of about 85% and an internal loss of 6.7 cm-1.
Unselective regrowth for fabricating 1.5-µm InGaAsP multiple-quantum well (MQW) distributed-feedback (DFB) buried heterostructure (BH) lasers is developed. The experimental results exhibit superior characteristics, such as a low threshold of 8.5 mA, high slope efficiency of 0.55 mW/mA, circular-like far-field patterns, the narrow linewidth of 2.5 MHz, etc. The high performance of the devices effectively proves the feasibility of the new method to fabricate buried heterostructure lasers.
A 1.60-µm laser diode and electroabsorption modulator monolithically integrated with a dual-waveguide spot-size converter output for low-loss coupling to cleaved single-mode optical fiber is demonstrated. The devices emit in a single transverse and quasi-single longitudinal mode with a side mode suppression ratio of 25.6 dB. These devices exhibit a 3-dB modulation bandwidth of 16.0 GHz, and modulator extinction ratios of 16.2 dB dc. The beam divergence angle is about 7.3×10.6 deg, resulting in 3.0-dB coupling loss with cleaved single-mode optical fiber.
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