High quality N-polar GaN films grown with varied V/III ratios by metal–organic vapor phase epitaxy. Issue 70 (27th November 2020)

• Record Type: Journal Article
• Authors: Li, Chengguo; Zhang, Kang; Qiaoyu Zeng, ; Yin, Xuebing; Ge, Xiaoming; Wang, Junjun; Wang, Qiao; He, Chenguang; Zhao, Wei; Chen, Zhitao
• Is Part Of: RSC advances. Volume 10:Issue 70(2020)
• Page Start: 43187
• Page End: 43192
• Publication Date: 2020-11-27
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d0ra07856e
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : N-polar GaN films (C, D, E, F) grown with varied V/III ratio show improved crystallinity and reduced impurity concentrations. Abstract : 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 c -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 18 cm −3 to 3.7 × 10 17 cm −3 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.