Fabrication and Optoelectronic Properties of AlN/ZnO Nanorods Heterostructure

Author:An Ni Amany Abdellah Abdelrahim Ali

Supervisor:wang jin zhong


Degree Year:2018





ZnO is an Ⅱ-Ⅵ oxide semiconductor,which has wide direct bandgap of 3.37eV at room temperature,and the binding energy of exciton as high as 60meV.Especially,ZnO with 1-dimensional(1D)nanostructures including nanorods and nanowires are promising in UV optoelectronic devices,because of their higher surface-to-volume ratios and the quantum confinement effects in low dimension materials.Unfortunately,due to a large number of nonradiative center defects at interface and electrons trapping by the surface states,the photocurrent of ZnO UV photodetectors(UV PDs)is still low.In the dissertation,ZnO nanorods(NRs)were grown by hydrothermal method and ZnO/AlN heterostructures were fabricated,in which AlN layers were used as buffer layer and capping layer on the ZnO NRs.Furthermore,the effects of AlN on ZnO optoelectronic properties were studied.The main research contents are as the following.The AlN films were deposited via radiofrequency(RF)magnetron sputtering,using AlN target.The effects of sputtering conditions on the crystal quality and surface morphology of AlN films were studied.The results indicated that the optimized sputtering parameters with AlN target for AlN films deposition are 300 W,1.0 Pa,40:20,300℃corresponding to RF power,working pressure,Ar:N2 ratio and substrate temperature,respectively.Additionally,the effect of post annealing on AlN films were also studied.The optimized post annealing is 600℃.ZnO NRs were grown by hydrothermal method.Furthermore,ZnO NRs/p-Si heterojunctions were fabricated with and without AlN buffer layers between ZnO and Si substrates.Then the effects of AlN layers on ZnO/p-Si heterojunction optoelectronic properties were studied in detail.The results indicated that,after introduced AlN layers,the PL peak intensity of ZnO NRs/p-Si increase 4 times compared with that without AlN layers under the same excitation conditions.That attributed to an improvement in ZnO NRs crystallinity and quantum confinement effects by AlN potential barrier layers.ZnO NRs/p-Si heterojunctions with AlN capping layers were fabricated with sputtering techniques and their optoelectronic properties were studied.After covered with AlN films,the PL peak intensity of ZnO NRs/p-Si increase 3 times compared with that without AlN cover layers under the same excitation conditions.That attributed to the surface passivation effects,suppressed the non-radiative recombination besides the quantum confinement effects.UV PDs based on ZnO NRs/p-Si heterojunctions were fabricated with and without AlN capping layer.Under voltage bias of 5.0 V,the response wavelength of the photodetectors is about 365nm.After AlN capping layers introduced,the photodetector responsivity is improved about 7 times.The rise time and decay time is shortened from135 to 27 ms and 350 to 71 ms,respectively.