Schilirò Emanuela, Giannazzo Filippo, Di Franco Salvatore, Greco Giuseppe, Fiorenza Patrick, Roccaforte Fabrizio, Prystawko Paweł, Kruszewski Piotr, Leszczynski Mike, Cora Ildiko, Pécz Béla, Fogarassy Zsolt, Lo Nigro Raffaella
CNR-IMM, Strada VIII, 5, 95121 Catania, Italy.
Top-GaN Ltd., Sokolowska 29/37, 01-142 Warsaw, Poland.
Nanomaterials (Basel). 2021 Dec 7;11(12):3316. doi: 10.3390/nano11123316.
This paper reports an investigation of the structural, chemical and electrical properties of ultra-thin (5 nm) aluminum nitride (AlN) films grown by plasma enhanced atomic layer deposition (PE-ALD) on gallium nitride (GaN). A uniform and conformal coverage of the GaN substrate was demonstrated by morphological analyses of as-deposited AlN films. Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) analyses showed a sharp epitaxial interface with GaN for the first AlN atomic layers, while a deviation from the perfect wurtzite stacking and oxygen contamination were detected in the upper part of the film. This epitaxial interface resulted in the formation of a two-dimensional electron gas (2DEG) with a sheet charge density n ≈ 1.45 × 10 cm, revealed by Hg-probe capacitance-voltage (C-V) analyses. Nanoscale resolution current mapping and current-voltage (I-V) measurements by conductive atomic force microscopy (C-AFM) showed a highly homogeneous current transport through the 5 nm AlN barrier, while a uniform flat-band voltage (V ≈ 0.3 V) for the AlN/GaN heterostructure was demonstrated by scanning capacitance microscopy (SCM). Electron transport through the AlN film was shown to follow the Fowler-Nordheim (FN) tunneling mechanism with an average barrier height of <Φ> = 2.08 eV, in good agreement with the expected AlN/GaN conduction band offset.
本文报道了通过等离子体增强原子层沉积（PE-ALD）在氮化镓（GaN）上生长的超薄（5纳米）氮化铝（AlN）薄膜的结构、化学和电学性质的研究。通过对沉积态AlN薄膜的形态分析，证明了GaN衬底上有均匀且保形的覆盖。透射电子显微镜（TEM）和能量色散谱（EDS）分析表明，对于最初的AlN原子层，与GaN形成了清晰的外延界面，而在薄膜上部检测到偏离完美纤锌矿堆积和氧污染。这种外延界面导致形成了二维电子气（2DEG），其面电荷密度n≈1.45×10 cm，这是通过汞探针电容-电压（C-V）分析揭示的。通过导电原子力显微镜（C-AFM）进行的纳米级分辨率电流映射和电流-电压（I-V）测量表明，电流通过5纳米AlN势垒的传输高度均匀，而通过扫描电容显微镜（SCM）证明了AlN/GaN异质结构具有均匀的平带电压（V≈0.3 V）。电子通过AlN薄膜的传输遵循福勒-诺德海姆（FN）隧穿机制，平均势垒高度<Φ>=2.08 eV，与预期的AlN/GaN导带偏移高度一致。
