Research On Semiconductor Light-emitting Diodes Based On Van Der Waals Heterojunction

High-intensity light-emitting diodes(LED)are the continuous pursuit of the scientist,ever since LEDs have turned out to be widely adapted electrically generated light-emitting sources in modern society.The applications and significance of LEDs range from a very basic general illumination to the advanced photonic integrated circuits.?-? compound semiconductor-based LEDs are well commercialized by realizing blue light LED and white light LED successfully.In recent years,the silicon(Si)based and Si compatible high electroluminescence(EL)LEDs have gained enormous attentions because of their vital role in the rapidly growing field of Si-based photonic integration platforms.The contemporary heterogeneous CMOS technologies hardly achieved the integration of ?-? compound semiconductor-based devices on Si,which is crucial for integrated photonic devices.In the present study,we have demonstrated high EL LEDs based on Si and ?-? compound semiconductors,by introducing graphene as an interfacial layer between n-type and p-type semiconductors.Graphene is the key component for illumination from the LED,by acting as a hot electron accumulating layer.Herein,we have designed n-type(Si or ?-?)/thick dielectric layer/graphene/p-type ?-?(p-GaN,p-AlGaN)vertical semiconductor heterostructure based hot electron LEDs via the van der Waals integration method,which involves the physical assembly of the device components and that allows flexibility in device design.At applied forward voltages,the accelerated high energy electrons or hot electrons at the interface of semiconductor/dielectric can cross the dielectric barrier and accumulate at the graphene.The graphene layer may amplify the numbers of electrons through multiplication exciton effect.These excess hot electrons at graphene can be efficiently transferred into the p-type semiconductor leads to the radiative recombination and results in enhanced EL.In a comparative study,graphene free LEDs have not shown noticeable EL,because the appropriate thickness of the dielectric layer results in marginal electron tunneling,and hot electron-impact ionization will be the predominant phenomenon for electron transfer through the dielectric layer.Further,the Coulomb scattering and defects related scattering of charge carriers at the p-type ?-? semiconductor results in electron-lattice interactions leads to nonradiative recombination.In graphene-based LEDs,superior electron mobility,strong electron to electron interaction,and high conductivity along the planes of graphene enable the effective collection of the incoming hot electrons through the dielectric layer,and these hot electrons at graphene efficiently transferred into the p-type semiconductor by subsiding the Coulomb scattering results in enhanced EL.To emphasize the vital role of graphene,we made a study on n-type doping of graphene and about its implications on the enhancement of EL from the LED.We also worked on the 3D-3D(Three dimensional)van der Waals integrated semiconductor heterostructured LEDs based on the combination of n-(ZnO/MoO_x)/p-GaN.Realizing U? emission from ZnO/GaN-based LEDs is uncommon but significant,herein by introducing n-MoO_x,a well-known hole transport layer and electron blocker between ZnO and GaN,we have demonstrated the pure U?-EL in both forward and reverse bias.MoO_x as an interfacial layer can restrict the electron movement from n-ZnO to the p-GaN and facilitates the holes availability at the ZnO site,leads to the radiative recombination at ZnO with pure U?-EL.