Research On Heteroepitaxy Of Low Dislocation GaN On Silicon Substrate With Micro-nano Structures

Ⅲ-Ⅴ compound semiconductor materials represented by gallium nitride(GaN)can be widely used in light-emitting diodes,lasers,high frequency and high-power devices due to their excellent physical properties such as direct band gap and wide band gap.Silicon(Si),which serves as the foundation of the semiconductor industry,is the favored substrate due to its low cost and ideal manufacturing process.The silicon-based Ⅲ-Ⅴ integration that combines the advantages of Ⅲ-Ⅴ and Si has significant scientific and economic effects.Direct epitaxial growth of GaN single crystals on silicon substrates is the most effective method for achieving cost-effective and compatible silicon-based integration.GaN materials obtained by heteroepitaxy on silicon substrates,however,have an extremely high dislocation density due to the significant lattice mismatch and thermal mismatch between GaN and Si,which severely limits the use of silicon-based GaN integration.Therefore,obtaining high-quality heteroepitaxy of gallium nitride on silicon substrates is a serious barrier to overcoming high-performance Ⅲ-Ⅴ siliconbased integrated applications.In this paper,a series of solutions based on micro-nano structures were proposed to realize silicon-based heteroepitaxial GaN materials of high quality and low dislocation density.This study employed a number of silicon-based heteroepitaxy growth techniques based on micro-nano structures,including compliant substrates and selective area epitaxy.The following are the primary research findings and innovations:1.A nano-deep hole-based epitaxial growth scheme for low dislocation GaN on patterned Si substrate was proposed.This structure had a higher aspect ratio of nanoholes(up to 15)than any other comparable structure ever published in the literature.On this silicon substrate,GaN was grown utilizing MOCVD technology.GaN nanowire epitaxy with extremely low through dislocation density was achieved by fully filtering out dislocations using the nano-aperture and high aspect ratio characteristics of the micronano structure pattern.The underlying physical mechanism of dislocation filtering in the nano-deep hole structure was further explored based on the observation of the dislocation characteristics in TEM images and the mirror force model.2.Based on the nano-deep hole structure silicon substrate proposed in this paper,a scheme for epitaxial growth of GaN nanowalls based on a high aspect ratio nano-long slot structure silicon substrate was proposed for comparison.The effect of nano-long groove substrate filtering through dislocations in GaN epitaxial is investigated by analyzing and comparing the morphological characteristics of SEM and TEM characterization of epitaxial GaN in nano-long groove and nano-deep hole silicon substrates,as well as the theoretical calculation of GaN epitaxial critical thickness.In contrast to the nano-deep hole epitaxial method on silicon substrate,a scheme that was more appropriate for the epitaxial growth of GaN on large-area low-dislocation silicon substrate was thus obtained.3.A scheme for epitaxial GaN based on a two-layer serpentine channel structure was realized on a silicon substrate.The filtering phenomenon of the the through dislocation under the bending of the two growth surfaces of the serpentine channel was observed by the TEM characterization of the silicon-based epitaxial sample with the structure.The physical mechanism of GaN heteroepitaxial filtering dislocation on the silicon-based serpentine groove substrate was explained in combination with theoretical analysis.This approach to growing a high-quality GaN epitaxial layer on silicon based on a serpentine channel substrate has a wide range of adaptability,is simple to integrate with the current CMOS process,and has low requirements for nucleation and growth conditions.It can be extended to large-area heterogeneous epitaxy of other material systems,effectively improving epitaxial crystal material quality.4.A scheme for epitaxial Ⅲ-Ⅴ semiconductor materials on suspended nano-flexible substrates was proposed.Only 16 nm thick,this structure is thinner than the minimum thickness of comparable structures described in the literature.Low dislocation epitaxy of GaN on suspended structure was realized by the low cost,easy fabrication and no transfer process.The physical principle of high-quality epitaxy of suspended nanoflexible substrates through stress release was investigated through HRTEM characterization combined with simulation analysis,and the theoretical explanation of the conventional flexible substrate epitaxy model was supplemented and optimized.In conclusion,this paper investigated the effective reduction of high mismatch in silicon-based GaN epitaxial dislocation through a variety of micro-nano structure design,which was systematically realized in nano-holes,nano-trenches,serpentine channels,and plane compliant substrates,with the size from small to large.Low dislocation Sibased GaN heteroepitaxial growth was achieved by these methods.