Chuang Chun-Wei, Hong Franklin Chau-Nan
Department of Chemical Engineering, National Cheng Kung University, 1 University Road, Tainan70101, Taiwan.
ACS Omega. 2022 Oct 21;7(43):38289-38298. doi: 10.1021/acsomega.2c02204. eCollection 2022 Nov 1.
The heteroepitaxial growth of vertically aligned gallium nitride (GaN) single-crystalline microrod arrays on silicon substrates was achieved with high reproducibility by using the plasma-enhanced chemical vapor deposition (PECVD) method in the furnace. By reducing the plasma power from 70 to 15 W, the crystal morphology of GaN varied from thin films to microrod arrays with the decreased V/III gas ratio. The growth of GaN crystals occurred in the vertical direction of the substrate and in the lateral direction of the growth axis via the self-catalytic vapor-liquid-solid mechanism (VLS mechanism) and the vapor-solid mechanism (VS mechanism), respectively, contributing to the formation of inverted hexagonal GaN cone microrods. Furthermore, the morphology of inverted hexagonal GaN cone microrods shows extremely small contact areas between the microrods and the substrate, suggesting the potential to solve the problems of stress accumulation and poor crystalline qualities of heteroepitaxy. With the raised growth temperature of GaN from 930 to 980 °C, the material quality was improved and the high crystalline qualities were obtained, owing to the successful surface migration of gallium atoms. However, the density of GaN microrods became lower with the increased growth temperature because the spatial temperature gradient was reduced and the evaporation of gallium was enhanced, leading to fewer gallium atoms precipitating and remaining on the substrate. The growth direction of vertically aligned GaN single-crystalline microrod arrays with the (002) crystal plane is along the [0001] orientation ( axis) and normal to the substrate surface, which may bring about many device applications in future studies.
通过在炉中使用等离子体增强化学气相沉积（PECVD）方法，在硅衬底上实现了垂直排列的氮化镓（GaN）单晶微棒阵列的异质外延生长，且具有高重现性。通过将等离子体功率从70 W降低到15 W，随着V/III气体比的降低，GaN的晶体形态从薄膜变为微棒阵列。GaN晶体的生长分别通过自催化气-液-固机制（VLS机制）和气-固机制（VS机制）在衬底的垂直方向和生长轴的横向方向上发生，有助于形成倒六角形GaN锥形微棒。此外，倒六角形GaN锥形微棒的形态表明微棒与衬底之间的接触面积极小，这表明有可能解决异质外延中的应力积累和晶体质量差的问题。随着GaN生长温度从930℃升高到980℃，由于镓原子成功地进行了表面迁移，材料质量得到改善并获得了高晶体质量。然而，随着生长温度的升高，GaN微棒的密度降低，因为空间温度梯度减小且镓的蒸发增强，导致在衬底上沉淀并保留的镓原子减少。具有（002）晶面的垂直排列的GaN单晶微棒阵列的生长方向沿着[0001]取向（轴）且垂直于衬底表面，这可能在未来的研究中带来许多器件应用。
