| UV light has significant value in the field of screen printing, polymer curing,environmental protection, white lighting, as well as military detection. AlGaN as a Ⅲ-nitridematerial which has a direct band gap and its bandwidth continuously variable from3.4eV to6.2eV, wavelength range covering200nm-365nm UV wave is an ideal material forpreparation ultraviolet DUV LED. Based on the outstanding performance in low and far fromequilibrium growth for molecular beam epitaxy and its better interdiffusion than Metalorganic chemical vapor deposition.In this work, high quality of AlN、AlGaN films andAl0.75Ga0.25N/Al0.45Ga0.55N MQWs were prepared by means of molecular beam epitaxy.The main results are as follows:1.The influence of increasing the growth temperature of AlN films, insert thelow-temperature AlN buffer layer increases the III/Ⅴ ratio during the growth of of AlNthin films by molecular beam epitaxy. The study found that the growth temperature is littleimpact on a screw dislocation, edge dislocation density decreases with increasing temperature.The buffer layer on the edge dislocation and screw dislocation density is a couplingrelationship, and to reduce the screw dislocation will increase the density of edge dislocations,the lower edge dislocation density will also increase the screw dislocation density. Of Al/Nbeam than for the surface morphology of AlN films. The growth of nitrogen-rich surface isvery uneven, in the case of Al-rich, the surplus of Al metal layer can effectively improve thesurface roughness of AlN in, but too much of the Al metal will lead to the surface of Al metalresidues, which is generally said Al-droplets.2.Al composition graded layer was inserted between the AlN film and theAl0.45Ga0.55N to reduce the stress generated due to lattice mismatch, reducing thedislocations generated in the heteroepitaxil interface. studied the impact of the Al compositiongraded layer to the AlGaN layer. The XRD AlGaN film (002) surface of the peak half-widthfor143arcsec show that the Al composition gradient layer for reducing dislocations in thecrystal to improve the quality of the AlGaN crystal to a certain extent. AFM testing a flatsurface, you can see the clear atomic steps, the RMS is only1μm×1μm range0.48nm,indicating the AlGaN film has a flat surface.3.Five cycles of the quantum well Were prepared by, which barrier thickness is5nmand Al composition was75%, the thickness of the wells, respectively3nm,2nm,1nm and Alcomposition were45%. Studed the influence of different well thickness for the internalquantum efficiency of the quantum well. Study found that the quantum well emissionwavelength at280nm, with the well width decreases, the wavelength blue shift, while thelight intensity becomes weaker. On the one hand, the quantum confined Stark effect caused on the carrier wave function in quantum wells offset which lead to the carrierrecombination rate decreases. On the other hand, the XRD results show that there has noobvious satellite peaks, that indicate the quantum well interface is not sharp, rough interfaceform an non-radiative recombination centers in quantum wells, resulting in weak quantumwell light-emitting intensity.Studies have shown that with higher growth temperature，the film will grow inthree-dimensional mode under the metal-rich environment in molecular beam epitaxyequipment, and the introduction of low-temperature AlN buffer layer can get the high crystalquality and surface roughness of AlN template. Al composition gradient layer can reduce thedislocation density in the AlGaN material. Further optimize the growth conditions of AlGaNquantum wells, and control the flatness of the interface, the high internal quantum efficiencyAlGaN quantum wells will be got. |
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