Work function investigations of Al-doped ZnO for band-alignment in electronic and optoelectronic applications
Work function investigations of Al-doped ZnO for band-alignment in electronic and optoelectronic applications
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DOI：
10.1016/j.apsusc.2019.04.079
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发表时间：
2019-08-01
影响因子：
6.7
通讯作者：
Lee, Sunghwan
中科院分区：
文献类型：
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作者：
Drewelow, Grant;Reed, Austin;Lee, Sunghwan
具有调节透明导电氧化物（TCO）的功函数和带隙的能力受到广泛追捧，因为它允许在电子和光电应用中改善能带对准，从而增强整体器件性能。在众多TCO中，Al掺杂的氧化锌（AZO）由于其低电阻率、在可见光范围内的高光学透明度以及室温制造能力而在电极应用中受到相当大的关注。在这项研究中，我们报告的影响后制造空气退火的功函数和带取向的AZO沉积在室温下通过直流磁控溅射。AZO膜在从25摄氏度（沉积态）到600摄氏度变化的温度下空气退火。通过X射线光电子能谱（XPS）和紫外-可见光谱（UV-Vis）研究了AZO薄膜的费米能级、功函数值、表面化学和光学带隙。观察到在退火温度从25摄氏度（沉积态）增加到600摄氏度的过程中，功函数从类似于5.53 eV增加到类似于6.05 eV，这被确定为是通过促进氧空位的消光而降低载流子浓度的结果。通过XPS分析，增加消光的氧空位被证实，由于一个显着的转变，从缺氧状态到氧充足的状态，在高分辨率的O 1 s峰，其中的活化能被认为是33.3毫电子伏。在增加退火温度的过程中，光学带隙看到从类似于3.55 eV的位移到类似于3.37 eV，遵循Burstein-Moss现象，由于载流子浓度的降低，进一步验证了氧空位消光的增加。报道的结果证实，AZO薄膜的功函数调谐可以通过简单的制造后空气退火来实现。
Possessing the ability to tune the work function and band gap of transparent conducting oxides (TCOs) is widely sought after, as it allows for improved band alignment in electronic and optoelectronic applications, enhancing overall device performance. Out of the many TCOs, Al-doped zinc oxide (AZO) has received considerable interest for electrode application due to its low electrical resistivity, high optical transparency in the visible regime, and room-temperature fabrication capability. In this study, we report on the effects of post fabrication air-annealing on the work function and band alignment of AZO deposited at room temperature by DC-magnetron sputtering. AZO films were air-annealed at temperatures varying from 25 degrees C (as-deposited) to 600 degrees C. The Fermi energy levels, work function values, surface chemistry, and optical band gaps of the AZO films were investigated via Xray photoelectron spectroscopy (XPS) and UV-Vis spectroscopy. An increase of the work function from similar to 5.53 eV to similar to 6.05 eV is observed to take place over an increase of annealing temperatures from 25 degrees C (as-deposited) to 600 degrees C, determined to be the result of a decrease in carrier concentration through the promoted extinction of oxygen vacancies. Via XPS analysis, the increased extinction of oxygen vacancies was confirmed due to a notable shift from an oxygen-deficient state to an oxygen-sufficient state in the high resolution O 1s peaks, for which the activation energy was found to be 33.3 meV. Over the course of increasing annealing temperatures, the optical band gap saw a shift from similar to 3.55 eV to similar to 3.37 eV, following the Burstein-Moss phenomenon due to a decrease in carrier concentration, further verifying an increase in oxygen vacancy extinction. The reported results confirm that work function tuning of AZO films can be achieved through simple post-fabrication air-annealing.