Investigation On Optical Properties And Application Of Deep-ultraviolet AlGaN Low-dimensional Materials

At present,the lack of precise laser source in deep-ultraviolet regime seriously limits developments in deep-ultraviolet instruments and advanced technology.Semiconductor deep-ultraviolet laser has the advantages of high frequency,small size,low energy consumption,environment freindship and long life,which could be widely applied in the fields of sterilization,purification,disease treatment,information technology,microprocessor-based machining and so on.The research on the optical properties and luminescence mechanism of AlGaN low-dimensional materials is meaningful for fabrication of photoelectronic device,structure optimization of active region and improvement of luminescence efficiency.In this work,optical properties and carrier recombination characteristics of AlGaN quantum wells and AlGaN quantum dots were studied.Meanwhile,AlGaN quantum dots structure was attempted to fabricate optically pumped deep ultraviolet VCSEL devices.Problems and improvements in the samples were discussed as well.The main research contents include:(1)Optical properties of AlGaN multiple quantum wells and AlGaN quantum dots were studied and compared by excitation-power-dependent PL and temperature-dependent PL measurements.In excitation-power-dependent PL,fitting of intensity showed the differences of carrier combination between the structures at low temperature.Small shifts of peak position and FWHM indicated the weak polarization field in AlGaN quantum wells.Blue-shift of peak position in AlGaN quantum dots was caused by Coulomb shielding effect under the low excitation power and band-filling effect under high excitation power,respectively.In addition,variations of intensity,peak position and FWHM with temperature were analyzed by fitting with Arrhenius formula and using dynamics model of carrier migration,respectively.After comparison of the experimental results for two different strucrtures,it was clear that AlGaN quantum wells are featured with weak polarization field while AlGaN quantum dots are featured with strong quantum confinement effect.(2)We have simulated the intesity profile of resonant modes in the cavity,designed the process,performed device fabrication,and measured the device performances for AlGaN based optically pumped deep-ultraviolet VCSEL structure.The active region was perfectively align to the antinode of optical field,which increased coupling efficiency between the active region and optical field.We fabricated the VCSEL structures following the deposition of bottom DBR,bonding by wax,laser lift-off and deposition of top DBR.Photoluminescence measurements showed that cavity modes were at 305,314,323 and 335 run.However,threshold was not observed due to the large optical loss in the cavity.