Novel indium phosphide based broadband bipolar cascade lasers and broadband gain materials: Designs, MOCVD growth studies, and fabrications

Broadband multi-wavelength lasers and broadband gain materials have widespread applications in communications, spectroscopy, metrology, optical data processing and storage. In general, Non-identical Multi-Quantum Well (MQW) designs and complicated and bulky external cavities are used to achieve simultaneous multi-wavelength lasing. The existing designs are all based on vertical current injection (VCI) structure, which causes severe non-flat gain profiles and inferior quantum efficiencies due to the non-uniform carrier distribution among the tapered wells. These characteristics greatly restricted the devices' performance and applications.; This work focused on innovative device structures and designs to achieve multi-wavelength lasers and broadband gain materials. Two different designs were studied to resolve the foregoing problems. One is to use bipolar cascade laser (BCL) structure to achieve a compact InP based dual-wavelength laser. Simultaneous dual wavelength (1350nm and 1450nm) output at room temperature using pulsed excitation is achieved by epitaxially connecting two different active regions with a low area specific resistance (∼10 -4Ocm2) InAlAs/InP hetero tunnel junction (TJ). This is the first InP based multi-wavelength BCL to the best of my knowledge. By cascading more active regions, ultra-broadband gain materials may be achieved. In another design, lateral current injection (LCI) concept is adopted to circumvent the MQW carrier density distribution non-uniformity issues associated with VCI lasers to achieve a flat broadband gain. A novel LCI broadband gain device was proposed and developed also for the first time. The design considerations were studied and a simple fabrication process was used to get a flat gain covering 1300nm∼1550nm spectrum.; MOCVD was used for all epitaxial growths in this work. Several MOCVD growth techniques, which are seldom studied or only sporadically reported in the literature, were studied to achieve the unique device designs, improve performance and simplify the develop process. MOCVD carbon doping in In 0.52Al0.48As, In0.52Al0.2Ga0.28 As and In0.53Ga0.47As was studied. C-doped In 0.52Al0.48As with very high hole concentration (∼6x10 19cm-3) has been achieved and applied in a high performance In0.52Al0.48As/InP hetero TJ for multi-wavelength BCL application. The mechanism and methodology of MOCVD post-growth Zn diffusion in InP were investigated. Buried hetero-structure laser MOCVD regrowth process was also studied, and applied in bipolar cascade laser fabrication.