Highly Efficient AlGaN-based Deep Ultraviolet LED Through Band Engineering And Optical Field Modulation

Deep ultraviolet light-emitting diode(DUV LED)based on AlGaN material is recognized as one of the most promising new-generation ultraviolet light sources due to their environmental protection,stability,small size,etc.It has broad application potential in environmental disinfection,ultraviolet curing,military communications,and other fields.By adjusting the ratio of GaN and AlN in the AlGaN alloy,the emission wavelength of AlGaN material can be tuned from 210 nm to 365 nm,which meets the application requirements of different ultraviolet bands in various situations.However,at present,the efficiency of AlGaN-based DUV LED is limited,which is mainly caused by its poor internal quantum efficiency(IQE)and light extraction efficiency(LEE),and the performance decline is more obvious at shorter emission wavelengths.This limits the further improvement of DUV LED performance.To achieve more efficient DUV LEDs,we have designed and optimized the energy band and modulated the light field AlGaN-based DUV LED.The main works carried out are as follows:(1)A novel DUV LED structure without electron blocking layer(EBL)is demonstrated.By removing the EBL,which has high Al-content,it is beneficial to prepare higher epitaxial quality.In addition,the energy band structure can effectively inhibit the leakage of electrons and the efficiency droop under large current injection,because the special quantum barrier(QB)after the energy band design can better prevent the electrons overflow to the p-type region for non-radiative recombination.Meanwhile,the removal of EBL can effectively upgrade the hole injection.Compared with conventional DUV LED,this novel DUV LED structure without EBL achieves 48.5%LOP improvement at 120 mA injection current,according to the simulation result.(2)The performance improvement mechanism of N-polar DUV LED was explored,and the structural parameters of the active region,including QB,quantum well(QW)thickness,and the influence of EBL thickness and Al composition on the performance of N-polar DUV LED were studied.Different from conventional Ga-polar DUV LEDs,N-polar DUV LEDs have better electron confinement ability,so they are not sensitive to the thickness variation of QBs.However,as the quantum well becomes thicker,the LOP increases and gradually becomes saturated.In addition,although the electron blocking ability of N-polar DUV LEDs is better,too low EBL thickness and Al composition will reduce the device performance.(3)A micro-ring DUV LED was designed and fabricated.By preparing the mesa into concentric rings,the surface volume ratio of the device is greatly improved,and the larger side wall can effectively reflect the light emitted by the LED to the substrate and extract it,reducing the UV absorption of the GaN ohmic contact layer,therefore improves the LEE.The smaller mesa area also makes the micro-ring structure DUV LED have a higher communication bandwidth.Compared with the common LED structure,the LOP and communication bandwidth of the micro-ring LED structure are increased by 13.4%and 10.6%,respectively,at an injection current of 150 mA.