Preparation And Characterization Of LED Heterojunction Devices Based On Atomic Layer Deposited ZnO

Zinc oxide(ZnO)materials have great potential in the field of luminescence devices due to its large band gap(3.37 e V),high exciton binding energy(60 me V)and high background carrier concentration.In the past few decades,ZnO-based devices have attracted the interest of many research groups.There are a lot of reports on both ultraviolet and visible region LED based on ZnO.In a standard LED device,both n-type and p-type layers are necessary layers.Up to now,due to the intrinsic characteristics,most of the ZnO materials present n-type.Furthermore,the complexity and stability of p-type ZnO materials,it is difficult and inefficient to realize homogeneous junction LED devices based on ZnO.At present,the frequently-used p-type materials are gallium nitride(Ga N),silicon(Si)and so on.For the Ga N materials,the lattice constants,bandgap width and ZnO of Ga N materials match very well,and the crystal structure of Ga N materials is wurtzite structure,so Ga N is very suitable for p-type materials matching ZnO.For Si materials,because of the mature process,the p-type carrier concentration can reach an extreme high level,so it is very suitable as a hole injection material.In this paper,the band and electroluminescent properties of LED devices based on ZnO fabricated by ALD method are studied.The main research results are as follows:1.ZnO thin films were grown on p-Ga N substrates by atomic layer deposition(ALD)technique to form heterojunction light emitting diodes(LED).Zirconium dioxide(Zr O₂)thin films were grown by ALD technology as the insertion layer of ZnO/Ga N heterojunction to adjust the energy band and carrier recombination.By introducing Zr O₂thin layer,the growth orientation of ZnO thin films changed from<0002>to<101?0>.X-ray photoelectron spectroscopy(XPS)band alignment results show that,a new energy level was introduced to the heterojunction due to the Zr O₂ thin layer,resulting in the strengthen of the specific electroluminescence peak.The light emitted by the ZnO/Zr O₂/Ga N heterojunction under a certain reverse current(10 m A)is very close to white light,and its CIE coordinates are(0.305,0.357).2.The p-type silicon(p-Si)with low resistivity is used as the p-type layer instead of p-Ga N to form heterojunction LED with ALD-ZnO,and the Zr O₂ grown by ALD was also used as the intermediate insertion layer.The energy band localization was measured by XPS.The heterojunction LED can emit very weak yellow and white light under a certain positive bias.The ALD-grown nickel oxide(Ni O)films are introduced in to replace the interlayer(Zr O₂)as the intermediate electronic barrier layer,and heterostructured LED devices are formed.The results show that Zr O₂ provides a good barrier for the heterojunction in conduction band,but there is no hole barrier in valence band.The heterojunction light-emitting devices consisting of organic materials instead of p-type and ZnO materials emit blue light,the organic materials is PEDOT:PSS.3.Transparent and conductive Al-doped zinc oxide(AZO)was grown on p-Ga N substrates by polymer-assisted deposition(PAD)technology.Due to the unique characteristics of PAD process,good ohmic contact was formed between AZO and p-Ga N.Then,ALD technology was introduced to grow low resistivity AZO on the AZO grown by PAD technology to further reduce the contact series resistance,and its mechanism was studied.In this paper,we mainly use ALD technology to grow ZnO-based LED devices,and suitable insertion layers and p-type layer were chosen to form LED devices.At the same time,we use PAD method to form good ohmic contact on Ga N.