Thesis Examination Committee
Prof Ning WANG, PHYS/HKUST (Chairperson)
Prof Kei May LAU, ECE/HKUST (Thesis Supervisor)
Prof Aaron Ho Pui HO, Department of Biomedical Engineering, The Chinese University of Hong Kong (External Examiner)
Prof Andrew Wing On POON, ECE/HKUST
Prof Man WONG, ECE/HKUST
Prof Jiannong WANG, PHYS/HKUST
Quantum dot (QD) lasers operating in datacom and telecom wavelengths (1.3 and 1.55 μm) have been significant building blocks in inter/intra-chip optical interconnections as well as long-haul communications. Although significant advances have been achieved in improving the performance of the QD lasers, most of them have only been realized on the native GaAs or InP substrates. It has been a long-standing desire to monolithically integrate these high-performance lasers on silicon, which enables wafer-scale photonic integrated circuits on the basis of CMOS manufacturing platform for silicon photonics.
In this thesis, we aim to produce efficient III-V quantum dot lasers epitaxially grown on Si substrates, emitting at the 1.55 μm band. To realize this goal, challenges have to be settled, which mainly lie in achieving good QDs with strong optical emission together with a uniform QD distribution, as well as obtaining a smooth InP buffer grown on Si substrates with minimized defects generation. By utilizing the double-cap procedure, we were able to stack the InAs/InAlGaAs QDs to enhance the optical properties; additionally, these self-assembled QDs were inserted into the InP buffer to serve as dislocation filters.
Based on these efforts, low-temperature continuous-wave (CW) operation of QD microdisk lasers (MDLs) grown on (001) Si was realized. To miniaturize the footprints of the microlasers, subwavelength QD MDLs were produced, showing low thresholds, superior characteristic temperatures and above room temperature operation, under pulsed optical pumping.
Furthermore, we moved on to grow and fabricate the more practical electrically injected Fabry-Perot lasers. By carefully tuning the growth parameters of QDs and leveraging the V-grooved Si to lower dislocation densities in the QD laser structure, the first 1.55 μm band room temperature electrical QD laser directly grown on Si was demonstrated, with a threshold density as low as 1.8 kA/cm2, and a high operation temperature up to 80°C.