Study On Application And Optimization On AlGaN Based Deep Ultraviolet LED

The solid-state deep ultraviolet(DUV)lighting sources,radiation with a wavelength shorter than 290 nm,are finding a variety of applications including air and water purification,UV curing,medical instrumentation,high-density optical storage,and non-line-of-sight communication.Due to direct and tunable band gaps between 3.4 and 6.2 eV,AlGaN alloys are very promising materials in the realization of DUV light emitting diodes(LEDs).There are a number of problems on the control of the material's conductivity.one of the difficulties lies in very low Mg-doped efficiency in Al-rich AlGaN alloys.High acceptor ionization percentage would create a significant improvement on the device's external quantum efficiency(EQE).Next,The cairriers distribute uniformly resulted from the optimization to the active region's structure,which improves the radiative recombination rate of DUV LEDs as well as light emission intensity.Another problem for AlGaN-based DUV LEDs is only a small light escaping angle.Significant part of light is trapped by total internal reflection resulting in very low light extraction efficiency.An effective method to avoid the trouble is fabricating high reflectivity distributed Bragg reflector(DBR)in DUV LEDs.Besides,the high quality DBR is most likely approach to achieve strong coupling between excitons and photons.In this work,we investigate numerically the effects of p-type electron blocking layer,optimized active region,and fabricated DBR on characteristics of AlGaN-based DUV LEDs.At last,a non-line-of-sight communication system has been developed based on DUV LEDs light source.The main conclusions are listed as follows:1.We present a DUV LED with 6-periods MQWs PIN(p-type/intrinsic undoped/n-type)structure.Investigate numerically performances of DUV LEDs by silvaco software.The forward voltage at 20mA for DUV LEDs are as low as 5.5 V.Interpret theoretically the influences of electron blocking layer's thickness and Al-content on turn-on voltage and light intensity.2.Reported the effects of incorporating Ga-face polarization-doped AlGaN p-type layer and the performance of DUV LEDs with intentionally increased the Al composition of LQB by using the silvaco simulation program.The characteristics of the DUV LEDs(?=270 nm)with polarization-doped AlGaN p-type layer have been studied and compared to DUV LEDs with Mg-doped AlGaN p-type layer(known as a conventional structure).The DUV LEDs fabricated using polarization-doped AlGaN p-type layer exhibited improved performance as evidenced by higher electroluminescence(EL)intensities,enhanced radiative recombination rate,and more steep rectification characteristics.Other than increasing the Al content of EBL,the Al content of last quantum barrier(LQB)has been increased to same with the maximum Al content of polarization-doped layers(PDLs),which causes to bent upwards in the conductive band of LQB,can effectively enhanced electron blocking and almost absolutely eliminated the accumulation of the leaked electrons.3.We have firstly reported that AlGaN-based solar-blind ultraviolet(UV)distributed Bragg reflectors(DBRs)were developed empolying a tri-layer AlGaN/AlInN/AlInGaN periodical structure grown on an Al0.5Ga0.5N template by metal-organic chemical vapor deposition.A state-of-the-art DBR structure was achieved thanks to the use of AlGaN template and the intentional design of the AlInGaN strain transition layer.The fabricated DBR exhibits a peak reflectivity of 86%at the center wavelength of 274 nm and a stopband with 16 nm full-width at half maximum.The simulation results of reflection spectra show that the use of a suitable AlInN layer replacing partially the AlGaN quarter-wave stack can reduce efficiently residual absorption in the stopband of the solar-blind UV DBRs and hence improves the DBR's reflectivity.4.We have study the drive scheme of modulating LED with ampere level current and millions hertz velocity.This scheme could be extend to drive LED array that may improve power from light source by composing of a series of LEDs and detect UV light power on micro watt scale that may realize ultra-long-distance communication.At last,we have design a non-line-of-sight communication system based on deep ultraviolet light source and photoelectric multiplier tube and realize a reliable serial communication at an baud rate of 115.2 kbps.