The fabrication and characterization of double waveguide ridge terahertz quantum cascade laser

• Main Author: Li, Jinghao
• Other Authors: Wang Qijie
• Format: Theses and Dissertations
• Language: English
• Published: 2018
• Subjects: DRNTU::Engineering::Electrical and electronic engineering
• Online Access: http://hdl.handle.net/10356/76013
• Institution: Nanyang Technological University

Terahertz technology shows broad application prospects in many fields. The development on the sources and detectors operating in terahertz range is always the key part of terahertz technology research. Terahertz quantum cascade laser (THz QCL) has been verified as a most promising coherent terahertz radiation source. There are some relatively mature theoretical models to describe the working principle of the terahertz QCL. There are several active region structures and resonator cavity designs developed to improve QCL lasing performance. Chirped superlattice, bound-to-continuum and resonant-phonon structure are the main active region structure designs of terahertz QCL. The three-well resonantphonon structure is one of the most effective and successful designs. Ridge structure laser is a common type of terahertz QCL, forming a Febry-Perot resonator cavity with the ends of ridge. The ridge QCL laser usually requires a waveguide design. The double-metal waveguide is a most widely-used scheme, which can realize a nearly 100% modal confinement. The ability to make a double-metal based waveguide ridge laser is very useful. Fabrication process largely determines the final quality of the device while the characterization result evaluates the performance of the ridge laser, which provides a good reference for QCL. In this dissertation, the theoretical analysis using the effective mass and envelop function approximation is reviewed in addition to the introduction of main active region designs and ridge structure with waveguide designs. A ridge QCL laser based on the three-well resonant-phonon and double-metal waveguide design was fabricated in the cleanroom facility. The detailed steps of the ridge laser fabrication process and significant factors with relevant failure modes are presented and discussed here, which can be used to instruct the fabrication of the ridge structure laser and other types of QCLs. To evaluate the lasing performance of the fabricated ridge laser, the light-currentvoltage curves at different temperatures from 9-145 K and the emission spectra with different pumping currents at 9 K were measured and are presented in the dissertation. The results demonstrate that this double-metal waveguide ridge QCL exhibits good lasing performance, which realizes a low threshold current density in the low-temperature environment and a high maximum operation temperature up to 145 K. The peak output power achieves nearly 1mW. The emission spectra under different pumping currents indicate an obvious blue shift of the emission peak with increasing current. This phenomenon results from the Stark effect.