Li Chengguo, Zhang Kang, Yin Xuebing, Ge Xiaoming, Wang Junjun, Wang Qiao, He Chenguang, Zhao Wei, Chen Zhitao
Institute of Semiconductors, Guangdong Academy of Sciences Changxing Road 363 Guangzhou Guangdong 510651 China
RSC Adv. 2020 Nov 27;10(70):43187-43192. doi: 10.1039/d0ra07856e. eCollection 2020 Nov 23.
We studied the growths and characterizations of N-polar GaN films grown with constant and varied V/III ratios in high-temperature (HT) GaN growth on offcut -plane sapphire substrates by metal-organic vapor phase epitaxy. It is found that growth with a constantly low V/III ratio resulted in a high crystallinity but a rough surface and a high oxygen concentration, whereas growth with a high V/III ratio led to a smooth surface but a high carbon concentration and a degraded crystallinity. The overall quality of the N-polar GaN epilayer cannot be effectively improved simply by tuning the V/III ratio. The growth with varied V/III ratios was conducted by lowering the V/III ratio in the initial HT-GaN growth and keeping the V/III ratio constantly high in the subsequent growth. Such a change of V/III ratio resulted in a 3D-to-2D like growth mode transition during the early stage of HT-GaN growth which helped reduce threading dislocations and suppress impurity incorporation. By optimizing the nucleation temperature and the thickness of the initial low-V/III-ratio layer, the minimum full-widths at half-maximum of (002̄)/(102̄) rocking curves obtained were 288/350 arcsec and the oxygen concentration was reduced significantly from 1.6 × 10 cm to 3.7 × 10 cm while keeping a hillock-free smooth surface morphology. The overall quality of the N-polar GaN films was considerably improved. We believe that this simple, yet effective growth technique has great application prospects for high-performance N-polar GaN-based electron devices.
我们通过金属有机气相外延法，研究了在高温（HT）下在非切割平面蓝宝石衬底上生长的具有恒定和变化的V/III比的N极性GaN薄膜的生长和特性。结果发现，以恒定的低V/III比进行生长会导致高结晶度，但表面粗糙且氧浓度高，而以高V/III比进行生长则会导致表面光滑，但碳浓度高且结晶度下降。仅通过调整V/III比并不能有效地提高N极性GaN外延层的整体质量。通过在初始HT-GaN生长中降低V/III比并在随后的生长中保持V/III比恒定来进行具有变化的V/III比的生长。这种V/III比的变化导致在HT-GaN生长的早期阶段发生从三维到二维的生长模式转变，这有助于减少位错并抑制杂质掺入。通过优化成核温度和初始低V/III比层的厚度，获得的（002̄）/（102̄）摇摆曲线的半高宽最小值分别为288/350弧秒，并且氧浓度从1.6×10¹⁹cm⁻³显著降低到3.7×10¹⁸cm⁻³，同时保持无小丘的光滑表面形态。N极性GaN薄膜的整体质量得到了显著提高。我们相信，这种简单而有效的生长技术对于高性能N极性GaN基电子器件具有巨大的应用前景。
