The Design And Growth For Deep UV AlGaN Quantum Structure

With wide applications of nitride semiconductors in new energy,power electronics and optoelectronic devices,the demand for nitride based quantum structure materials and devices is also increasing.In recent years,AlGaN semiconductors have become the research hotspot of compound semiconductors because of its direct wide band gap,high electron mobility and high breakdown field strength.AlGaN low-dimensional quantum structure has gradually entered the field of vision.Although a series of research progress has been made,how to accurately control the well barrier thickness and obtain the growth of two-dimensional quantum structure with steep heterogeneous interface and no component mutual diffusion is still an urgent problem to be solved,especially the theoretical exploration of the growth mechanism of high-quality two-dimensional quantum structure is still in the blank.In order to further improve the optical properties of AlGaN quantum structure and provide an ideal material base for optoelectronic devices in deep UV,we have made periodic and orderly nanorod structure by means of micromachining on the basis of the high-quality two-dimensional quantum structure preparation,and further clarified the luminescent properties of one-dimensional nanorod and the emergence of two-dimensional quantum structure In addition,we try to explore the structure and characteristics of optical microcavity formed by quantum structure.The work of this paper is mainly divided into the following aspects:1.Epitaxial growth and characterization of ultra-short period superlattices.The chemical potential field of GaN and AlN growth under different conditions will have a great influence on the formation enthalpy of surface adsorption in each growth stage.The simulation results show that when the environment is in the N-rich atmosphere,it is suitable to adsorb N atoms on the GaN surface of the GA terminal or the AIN surface of the al terminal.The reabsorption of Al atoms on the surface of N adsorption layer requires an Al rich growth environment,while the adsorption of Ga atoms does not depend on the environment.Under the guidance of theoretical simulation,ultra-short period superlattices with well barrier controllable were obtained by separation and growth mechanism.High resolution XRD and TEM observations show that the samples have a sharp and resolvable interface which is thin to the level of a single molecular layer.At room temperature,it was found that the main peak of cathodoluminescence was single narrow,and the energy was consistent with the prediction trend of theoretical simulation.2.Construction and characterization of(AlN)8/(GaN)2 ultra-short period superlattice nanorods.Using self-assembled polystyrene template,nanorod arrays with different periods and diameters were prepared.The Raman results show that the internal strain state of the nanorod changes significantly compared with the plane structure,and the cathodoluminescence peak also shifts blue.The luminescent intensity of the structures with diameters of 550 nm and 400 nm is higher,5.5 and 4.7 times higher than that of the plane structure,respectively.The combination of stress release,interface effect caused by side wall damage and composition fluctuation results in the difference of wavelength blue shift between different diameter nanorod.FDTD simulation shows that the optical extraction efficiency of the nanorod is higher than that of the plane structure,which is consistent with the observed optical emission trend.3.The design of photonic crystal microcavity for deep UV AlGaN materials.Using the plane wave expansion method and FDTD simulation,we can scan the change trend of the photonic crystal band of the hexagonal lattice nanocolumn with the duty ratio.It is found that the wavelength range of the photonic band gap of the nanocolumn structure with the same duty ratio as that in Chapter 5 does not conform to the spontaneous emission compliance band,so the influence of the photonic band gap on the optical characteristics of the nanocolumn array is further excluded.Then,the performance of the microcavity composed of tetragonal lattice and hexagonal lattice nanopore array is simulated synthetically,and the specific "defect" mode is introduced.It is found that when the duty cycle of the hexagonal lattice nanopore microcavity reaches 0.4,the limiting effect of the microcavity on the deep UV photons is obvious,and the cavity quality factor Q is as high as 3417.