異質介面電子結構用於半導體場效電晶體的 ALD Y2O3/GaAs介面研究

Abstract

在這項研究中，我們使用同步輻射光電子能譜研究了沉積在GaAs(001)-4 × 6表面上的ALD Y2O3的電子結構。對於沉積在GaAs上的ALD Y2O3，我們清晰地觀察到介面演變的每一步。 在第一個主題中，我們研究了tris(ethylcyclopentadienyl)yttrium [Y(CpEt)3]和H2O反應過程的機制。在僅有Y(CpEt)3的第一個半循環中，Y(CpEt)3前驅物駐留在有缺陷的As原子上，並經歷電荷轉移到As原子上。在隨後的H2O半循環中，H2O 去除了Y(CpEt)3-As鍵結的分子，隨後氧原子與下面的Ga原子鍵結。Ga-O-Y鍵的形成穩定了Y2O3薄膜和GaAs界面。由此產生的Y2O3中的Y-O配對開啟了下一個 ALD 系列的成長。 在第二個主題中，我們研究了週期性沉積在p-GaAs(001)-4 × 6上的ALD Y2O3 原子層的能帶偏移和表面偶極位能。價帶和導帶偏移以及界面偶極位能分別約為 1.75 eV、2.4 eV 和 0.46 eV。偶極的正方向指向外部，這表明Y(+)離子位於最上層，O(-)離子與GaAs的表面原子鍵結。 在第三個主題中，我們比較了在新生長的GaAs(001)-4 × 6表面上沉積的納米厚ALD Y2O3在超高真空(UHV) 600 °C退火前後的電子結構。我們使用原位X射線光電子能譜（XPS）和原位同步輻射光電子能譜（SRPES）技術，並讓樣品在生長和傳送過程中都在超高真空（UHV）下保持原始狀態，以研究這些樣品。在Y2O3薄膜中，通過超高真空（UHV）退火完全去除了表面的Y-OH鍵結和ALD過程中生成的純As原子。此外，在XPS的解析限度內未觀察到任何O的缺陷，表明O-Y鍵的完整性。超高真空（UHV）退火降低了Y2O3薄膜中的陷阱密度，使金屬氧化物半導體電容器（MOSCAP）的電容-電壓（CV）曲線測量中頻率分散降低。同時，豐富的 Ga-O-Y鍵有效地對GaAs表面進行了鈍化，並強烈穩定了Y2O3/GaAs介面，從而降低了介面陷阱密度（Dit）值，同時保持了高溫穩定性。

In this research, we used synchrotron radiation photoelectron spectroscopy to study the electronic structure of ALD Y2O3 on GaAs(001)-4 × 6. Clear observation of the interfacial evolution step by step was found for ALD Y2O3 deposited on GaAs. In the first topic, we studied the mechanism of the tris(ethylcyclopentadienyl)yttrium [Y(CpEt)3] and H2O process. In the first half cycle with only Y(CpEt)3, the Y(CpEt)3 precursors reside on the faulted As atoms and undergo a charge transfer to the As atoms. After the subsequent half cycle of H2O, H2O removes the Y(CpEt)3-As bonded atoms, and then the oxygen atoms bond with the underlying Ga atoms. The formation of Ga-O-Y bonds stabilizes the Y2O3 film and the GaAs interface. The resulting Y-O pairs of Y2O3 open the next ALD series. In the second topic, we investigated the band offset and surface dipole potential of periodically deposited ALD Y2O3 atomic layers on p-GaAs(001)-4 × 6. The valence band and conduction band offsets, as well as the interface dipole potential, are approximately 1.75, 2.4, and 0.46 eV, respectively. The positive direction of the dipole points outward, indicating that Y(+) ions are located in the topmost layer, and O(-) ions bond with the surface atoms of GaAs. In the third topic, we compared the electronic structure of nanometer-thick ALD Y2O3 grown on freshly grown GaAs(001)-4 × 6, both before and after ultra-high vacuum (UHV) annealing at 600 °C. In-situ X-ray photoelectron spectroscopy (XPS) and in-situ synchrotron radiation photoelectron spectroscopy (SRPES) with optimal surface sensitivity were employed to study the samples, and their pristine conditions were maintained under UHV between growth and characterization. In the Y2O3 film, surface Y-OH bonding and pure As atoms generated during the ALD process were completely removed through UHV annealing. Additionally, no detection of O defects was observed within the resolution limit of XPS, indicating the integrity of O-Y bonds. UHV annealing reduced traps in the Y2O3 film, resulting in less frequency dispersion in the measured capacitance-voltage (CV) curves of metal-oxide-semiconductor capacitors (MOSCAP). Simultaneously, the enrichment of Ga-O-Y bonds effectively passivated the GaAs surface and strongly stabilized the Y2O3/GaAs interface, leading to a lower interface trap density (Dit) value, while maintaining high-temperature stability.