Fabrication And Luminescent Properties Of ?-Nitride Materials With Nanostructure Arrays

Using semi polar(11(?)2)plane AlGaN material as the active region material of the deep ultraviolet light emitting diode(UV-LED)can effectively inhibit the quantum confinement Stokes effect that existed in the traditional C-plane AlGaN material.The AlGaN nanorod structure can greatly improve the light extraction efficiency(LEE)of the UV-LED.So the semipolar(11(?)2)plane AlGaN nanorod is of great scientific significance and research value for the fabrication of UV-LED with high external quantum efficiency.In this paper,the semi polar(11(?)2)plane AlGaN based MQWs nanostructures with an emission wavelength of 271.5 nm have been successfully fabricated by using metal-organic chemical vapor deposition and nanospheres etching technology.Compared with the planar structure,the PL luminous intensity of the nanostructures has been increased by two times.The main research contents and achievements of this paper are as follows:(1)The Lloyd's mirror two beams interference system is designed and constructed.The grating structure with a period of 284 nm and a duty cycle of 0.73 is successfully fabricated.On this basis,a new type of two-axis Lloyd's mirror interferometer is proposed.By establishing a theoretical model,the corresponding relationship between all parameters in the experimental system and the corresponding periodic array is revealed,including the use of polarization modulation to achieve different nanostructure shapes.In addition,the uniformity of the periodic array is studied,and it is found that it mainly depends on the size of the extended laser beam.In order to use the model better,a user-friendly software is developed,and all the functional modules are integrated.(2)A process of preparing quasi ordered nano array structure with self-assembled polystyrene spheres was developed.The hexagonal array structure with a period of 350 nm was prepared on a two inch substrate by this method.Nanorod structure with adjustable diameter(150-280 nm)was available by optimizing the etching process parameters,which provided support for the subsequent preparation of semi-polar AlGaN nanostructures.(3)Semi-polar(11(?)2)AlGaN MQWs with surface roughness as low as 1.7 nm were grown.Furthermore,the semi-polar(11(?)2)plane AlGaN MQWs nanostructure with the emission wavelength of 271.5 nm was fabricated by nanosphere etching technology.The photoluminescence intensity of the nanostructure is twice higher than that of the plane structure.Through the analysis of room temperature photoluminescence spectrum,we can see that there is no free exciton related first-order longitude-phonon-assisted emission that associated with defects in the nanorod structure.It can be concluded that one of the reasons for the enhancement of the luminescence is that the non-radiation recombination induced by defects is reduced.Meanwhile,the plane structure and nanorod structure have similar peak position shift with the change of excitation power.The peak position shift is very small,which shows that both the nanorod structure and the plane structure effectively inhibit QCSE.On the other hand,the light extraction efficiency of nanostructure and planar structure are analyzed by theoretical simulation.The other reason for the enhancement of the luminous intensity of nanostructures is that they achieve significant light extraction enhancement in both TE and TM modes compared with planar structures.