Study On Epitaxial Growth Of 2μm Semiconductor Laser Materials And Device Fabrication

The mid-infrared spectral region is of enormous interest as the practical realisation of optoelectronic devices operating in the 2-10μm wavelength range offers potential applications in a wide variety of areas including; optical gas sensing and environmental monitoring, free-space optical communications, infrared countermeasures, clean energy generation, biomedical and thermal imaging. For example, the mid-infrared contains the fundamental fingerprint absorption bands of a number of pollutant and toxic gases and liquids; methane (3.3μm), CO2 (4.6μm), CO(4.2μm), NOx (6.5μm) and SOx (7.3μm) require accurate, in situ multi-component monitoring in a variety of different situations (e.g. oil-rigs, coal mines, landfill sites,car exhausts) and in concentrations, ranging from ppb to almost 100%.The mid-infrared is very attractive for the development of sensitive optical sensor instrumentation. Not all compositions of InGaAsSb/AlGaAsSb type heterostructure are easily grown,there is a large miscibility gap,and serious carrier absorbtion. That significant affects the performance and application of multiple quantum-wells (MQWs) InGaAsSb/AlGaAsSb laser diodes, In this dissertation, the present research works were focused on 2μm MQWs InGaAsSb/AlGaAsSb lasers.1) Firstly, lattice constants, relevant for Al,In components were calculated. Energy bandgaps of AlGaAsSb and InGaAsSb used Glisson,include the bowing effects in the ternary bandgaps were described. To estimate the index of refraction,Adachi's model was used.The subband transion of MQWs InGaAsSb/AlGaAsSb was investigated under the Effective-Mass models and Schrodinger equatuion, the relationship for the C1 and HH ground state energy verus waveguide thickness were derived, respectively.2) Secondly, high quality AlGaAsSb of high Al composition, heavily n-type doped, and InGaAsSb were grown by accurately controlling growth temperature andⅤ/Ⅲratio. High quality InGaAsSb/AlGaAsSb MQWs were grown, with AlSb buffer layers,and InGaSb (Columnar Quantum Dots (CQDs) were realized by MBE.3) Waveguide thickness optimizations of InGaAsSb/AlGaAsSb structures have been systematically studied. Specifically, in the case of 1μm waveguide thickness, laser operation has been achived with threshold current Ith of 225mA. Max output power is about 16mW;In the case of 2.4μm waveguide thickness, the threshold current Ith=:420mA, output power is about 20mW. When temperature range from10℃to 60℃, lasing wavelength red shifts ratio is 2.8nm/℃.With the waveguide thickness increasing, carrier absorption and series resistance increase, resulting slope efficiency reduction and the threshold current increase. but the beam quality is improved.Result for this studied,we think the range of waveguide thickness is importance.4) For the first time, InGaAsSb/AlGaAsSb multi quantum well(MQWs) lasers with an emission wavelength around 2.0μm, using the separate-confinement asymmetric waveguide, have been designed and fabricated, showing high quantum efficiency and high power conversion efficiency at continuous-wave operation mode. At room temperature, the threshold current of the device is as low as 279mA, slope efficiency is 0.49W/A, the internal loss coefficient and the internal quantum efficiency are about 1.0 cm-1 and 86.1%, respectively. The maximum power conversion efficiency (PCE) is 35% at 323mA drive current; relatively narrow far-field vertical and parallel divergent anglesθ⊥=30.2°andθ∥=7.1°were achieved, respectively.The above results indicate that the Sb containing semiconductor laser material design and growth method and device fabrication method put forwarded and adopted in this paper were very effective and conducive to the research and applications of mid-infrared semiconductor lasers.