The Study Of Micro-nano Patterned Mask And Substrate Of Ⅲ-group Nitride Material

From the early 1990 s, the performance of nitride devices improve very quickly and the blue and green LEDs have been commercialized. FETs shown high performance in microwave, high power and high temperature. The preparation of high-quality IIIgroup nitride materials is always the base of application. However, Ga N cannot obtain by pulling method as the Si single crystal due to excessive demands to temperature, pressure. So, how to obtain high-quality and low defect density thin film materials is the key issues throughout the III-nitride materials and device research.In this paper, to improve the crystalline quality of the material and reduce the defect density, we analyze reducation mechanism of dislocation and explore a new method. Herein, we select the patterned micro- and nano- mask and substrate as a research direction. Patterned mask and substrate were researched in the last twenty years decades. However,the study of nanoscale mask and substrate is need more researching. Herein, we apply two methods: First, the self-organization of micro- and nano-dielectric sphere as patterned mask used to Ga N and Al Ga N overgrowth; the other method is sidewall growth Ga N on micro-nano patterned substrate by dry etching. On the one hand, we explored and optimized mask production and material growth in the main process. On the other hand, we analyzed characteristics of the materials and gives a theoretical explanation. The main results are as follows:1. First, we study hydrophilic of substrates and found that Si, sapphire, Si C substrate can obtain good hydrophilicity by spin-coating PS film and treating in oxygen plasma. Ga N substrate and PS films can obtain good hydrophilic only by treating in oxygen plasma. Moreover, by the use of spin coating method, we successfully fabricate the monolayer micro-nanospheres of different diameter masks.2. In addtion, we fabricate self-assemble monolayer silica microspheres mask with controllable area and density, and grow high quality Ga N films with low residual strain and improved optical properties, where the growth of Ga N is self-stopped beneath close-packed monolayer microspheres. It was found that the TDs are significantly reduced from from 1.3×109 cm-2 to 8.5×107 cm-2 due to blocking and bending of dislocations near the interface between Ga N and silica microspheres. The two-step growth and the self-stop growth result in additional reduction of TDs, and the larger diameter silica microspheres lead to bending of TDs much effectively. In addition, the inserted silica microspheres serve as mask and contribute dramatically to the reduction of residual strain from 1.05 GPa to 0.14 GPa in Ga N. After secondary mask the dislocation density of Ga N reduced from 1.3×109 cm-2 to 5 × 107cm-2.3. Moreover,we fabricate self-assemble monolayer silica microspheres mask with controllable area and density, and overgrow a-plane and semi-polar Ga N films. For the a-plane Ga N, this method significantly reduce dislocations and stacking faults in overgrowth layer. Dislocations only exist at the window region while Ga N in the lateral growth region is dislocation-free. For the semi-polar Ga N, the method significantly reduces dislocations in overgrowth layer, dislocations also only exist at the window region. And Ga N in the lateral growth region is dislocation-free, however, still produce a great amount of stacking faults. Moreover, optical properties of Ga N overgrowth layer are significantly improved due to the large reduction of dislocations. When 1000 nm silica microspheres was used as mask, PL emission intensity of overgrown Ga N is 19 times stronger than without mask. Meanwhile, the surface morphology is also improved. Finally, dislocation density of non-polar Ga N reduced from ~ 3×1010 cm-2 to ~ 5×107 cm-2. Dislocation density of semipolar plane Ga N reduced from ~ 1×1010 cm-2 to ~ 1×108 cm-2, the basal stacking fault density of semipolar plane Ga N is reduced from > 1×105cm-1 to ~ 5×104cm-1.4. And then, we fabricate self-assemble monolayer silica microspheres mask to obtain Ga N islands and study low and high Al composition Al Ga N overgrowth on these Ga N island by ultra-thin Al N/Ga N superlattices method. The results showed that ultra-thin Al N/Ga N superlattices method achieved high lateral growth rate and rapid coalescence. Several different planes shown different growth rate, such as {11ˉ22}> {1ˉ101}>(0001), respectively. Furthermore, Al Ga N on the inclined surface {11ˉ22} plane and {1ˉ101} plane grown little dislocation. But Al Ga N on top face(0001) plane release the mismatch stress in the middle of the top surface of Ga N islands and from dislocations. Finally, the method can obtain crack-free high Al composition Al Ga N film.5. Finally, we study sidewall growth of Ga N on Ga N nano-columns with Ti N mask. Ga N nano-columns ware fabricated by RIE etching. This is Ga N nano-columns array forming method without complex lithography process by the use of micro-nano-spheres as a mask. The the residual stress and dislocations of sidewall growth Ga N, especially edge dislocations, reduce significantly. Meanwhile, the luminescent characteristics of Ga N improved significantly. Finally, the dislocation density of Ga N estimated by TEM reduced from 2.2×109cm-2 to 6×108cm-2.In short, these two methods are dedicated to provide more mechanism of defects reduction, and to avoid the degradation of the material properties.