Carrier Concentration Determination In ZnO-related Semiconductors Based On Raman Scattering

With large band gap energy and high exciton binding energy,ZnO has attracted great atten-tion in light-emitting area in the past few decades.Intensive research has been reported regarding the fabrication,doping,device structure and nanostructure for ZnO.However,besides crystal growth and device fabrication,accurate characterization of the properties for materials is also fun-damental for possible applications in real life.For semiconductor materials like ZnO,electrical properties,especially carrier concentration,predominantly define the performance of the device,which makes it important in material characterization.With the rapid evolution in ZnO-based devices,complicated structure like multilayered and nano structure emerge.However,for tradi-tional methods in determining the electrical properties like Hall measurement,their application in these state-of-art structures is greatly limited.Thus,it is in great need for a versatile,quick and non-destructive characterization method for electrical properties in semiconductors.Raman spectroscopy is one of them.Based on detecting the coupling between plasmon and longitudinal optical phonons in polar semiconductors,Raman method can quickly and non-destructively extract the carrier concentration in semiconductors.Our work focuses on the ap-plication of Raman spectroscopy in carrier concentration determination in ZnO thin films and ZnO-based LED devices,which have great potential in achieving ultraviolet luminescence.The main contents of this thesis are as follows.1.First,the application of Raman spectroscopy in carrier concentration determination in ZnO thin films is discussed.ZnO samples with various carrier concentration were examined with excitation energy below and above the band gap.The results shows that only the above-band-gap excitation can probe the coupling effect in ZnO thin films without the interference from the underlying substrate.The behavior of 1LO mode under resonant conditions is then discussed and its relationship with both coupling effect and crystal defects is demonstrated.Consequently,a extraction method based on the 2LO modes instead of the 1LO ones is proposed to avoid the influence from crystal defects and is successfully applied in extracting the carrier concentration in ZnO samples.The 2LO-based method shows good consistency with Hall results when carrier concentration exceeds 1019 cm-3.2.Second,the aforementioned 2LO-based method is applied in ZnO-based LED devices.An electron concentration of n=1.21 × 1019 cm-3 is extracted from the top n-current spread-ing layer in the p-GaN/(ZnO/ZnMgO)MQWs/n-ZnO structure.The extracted result is eval-uated based on the comparison on EL performance and simulation results with a reference device,which proves the validity of the 2LO-based method in LED devices.