Design And Optimization Of AlGaN Tunneling Junction

AlGaN semiconductors as the third generation wide band gap semiconductor,with superior properties including a wide direct band gap,strong atomic bond,high thermal conductivity,good chemical stability and strong resistance to radiation and so on,offer broad prospects in optoelectronics,high-temperature and high-power devices and high frequency microwave device applications.Rely on direct wide band gap,,the band gap can be tuned in the range of 3.4 to 6.2 eV by adjusting the alloy composition in the favor of the band tailoring,which render AlGaN as an ideal material for light emitting diode(LED),laser diode and detector device in the ultraviolet(UV).Especially as the ultraviolet solid-state light source,compared to the conventional mercury lamp,AlGaN based optoelctronic devices has advantages in efficiency,start-up time,service life,monochromatic and stability in addition to light weight and small volume,energy saving and environmental protection.Although there are many advantages of AlGaN,the Mg acceptor activation energy in AlGaN is considerably large and the p type doping greatly limits the hole injection,which become the bottleneck of the efficient application of AlGaN.In order to improve hole injection,the tunneling junction is designed and employed in the deep UV LED structure,the dependence of the carrier injection on the Al composition,doping concentration and thickness is studied by APSYS software.Furthermore,an undoped InGaN is inserted between the p type and the n type layer,and the tunneling hole injection is improved by changing the thickness of the undoped InGaN.Estimated by WKB method,the tunneling probability of the optimized structure reaches the order of 10-7.It is observed in I-V curves that the mechanism of tunneling injection to UVLED devices exhibit more excellent electrical conductivity.Single emission peak appear in electroluminescence simulated at room temperature,with intensity higher than the traditional UVLED structure,internal quantum efficiency,light power and radiative recombination rate simulation further validates the increase of hole concentration in the active region.The radiation recombination rate is greatly improved,which further improve the optical power of the device.The graded A1 content tunneling junction is designed to adjust the band bending by the band offset between the graded components combined with the spontaneous and piezoelectric polarization of the AlGaN.The enhancement of carrier diffusion and drift mode is helpful to enhance the probability of tunneling in the tunneling junction.Simulation results show that the optimized Al content in the p+-AlGaN is linearly graded from 0.45 to 0.70,while the A1 component in n+-AlGaN is linearly graded from 0.70 to 0.45.The tunneling probability is estimated up to the order of 10-5.The I-V curve exhibits a nearly linear relationship above the turn-on voltage,which indicates that the deep UV LED with the graded Al content tunneling junction represents better electrical injection characteristics.Room temperature electroluminescence intensity is higher than that of deep UV LED without the graded Al content structure.The simulated internal quantum efficiency,light power and radiative recombination rate further demonstrate the increases of injected hole concentration into the active region with the graded A1 content tunneling junction.The resulting radiative recombination rate within the quantum well is improved,which provide a fertile base for further improvement of photoelectrical device in the deep UV with the high performance.