Design, Growth And Fabrication Of Near Infrared Scmicomductor Laser Based On GaAs

Experienced several decades of development, the performance of GaAs-basednear-infrared semiconductor lasers has become more sophisticated and exuberant.Numerous novel structures are proposed to improve near infrared semiconductorlasers, however limitted by the design of high-performance laser epitaxial structureand material growth. In this paper, the high-power near-infrared edge-emitting laser(EEL) and795nm vertical cavity surface emitting laser (VCSEL) required byrubidium atomic clock are developed by handling the relation of the material growthand device loss, waveguide structure and power, quantum-well gain andcavity mode.The main limits to the max power of edge-emitting laser are the electro-opticalconversion efficiency and catastrophic optical damage (COD). The main work isfocused on structure optimization because most important characteristics: internalloss, optical gain, quantum efficiency, the transverse-mode size are all determined bythe epitaxial layer. Firstly, for the basic808nm laser structure, optimized dopingprofiles are proposed to reduce the inernal loss as low as2cm-1. Then, large opticalcavity with increased waveguide is used to expand the transverse mode size resultingin decrease of divergence angle from43°to32°. Lastly, the asymmetric waveguideis developed to discriminate high-order modes remaining the low-order mode lasingwith low divergence angle. Asymmetric waveguide also reduces the carrier leakage from p-typed waveguide and cladding layers. Improved815nm devices reach opticalslope efficiency of0.59W/A (uncoated) and1.1W/A (coated). The max output underquasi-continuous current can reach7W from unpackaged devices.794.7nm VCSELs applied to miniaturized rubidium atomic clock demand lowpower-dissipation, high operating temperature, and narrow spectral linewidth.Optical gain of InAlGaAs strained quantum well and cavity mode at room and highterperature are calculated by Pics3D (Photonic Integrated Circuit Simulator in3D). Aself-consistent VCSEL model based on quasi3D finite element analysis is employedto investigate the temperature distribution and output of the proposed structure.Output of1mW with3-dB bandwidth of6GHz is obtained from a3μm apertureVCSEL under2.4mA current at temperature higher than340K. The opimized795nm VCSEL epitaxial structure is grown by Axitron200/4MOVPE system.High-quality InAlGaAs strained multiple quantum-wells with photoluminescencespectral half width of13nm is obtained. Cavity modes of2inch wafer distribute inthe range of792.5nm to788nm demonstrating high uniformity of the thicness.795nm VCSELs with aperture of75μm to95μm are fabricated by wet-etching andselective oxidation process. More than15mW is obtained at room temperature.lasing spectrum794.7nm (corresponding rubidium atomic clock transition centrelevel) is reached at52oC under100mA. The maximum operating temperatureexceeds80°C.