Structural, microstructural, and electrical properties of gold films and Schottky contacts on remote plasma-cleaned, n-type ZnO{0001} surfaces -: art. no. 103517
Structural, microstructural, and electrical properties of gold films and Schottky contacts on remote plasma-cleaned, n-type ZnO{0001} surfaces -: art. no. 103517
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DOI：
10.1063/1.1898436
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发表时间：
2005-05-15
影响因子：
3.2
通讯作者：
Smith, DJ
中科院分区：
文献类型：
--
作者：
Coppa, BJ;Fulton, CC;Smith, DJ
对沉积在非原位清洁的n型ZnO（0001）[（000（1）over bar）]表面上的Au接触的电流-电压测量显示，在4.6（3.75）V反向偏压下，反向偏压漏电流密度近似于0.01（近似于0.1）A/cm（2），并且在急剧永久击穿（软击穿）之前理想因子> 2（两个表面）。这种行为主要是由于氢氧化物的（1.6-2.0）+/- 0.1 [（0.7-2.6）+/- 0.1]单层（ML）的存在，其形成电子积累层并增加表面电导率。使用20 vol % O-2/80 vol % He混合物对（0001）[（000（1）over bar）]表面进行原位远程等离子体清洁，优化温度、时间和压力为550 +/- 20 ℃在525 +/-20 ° C）、60（30）min和0.050 Torr的条件下，将氢氧化物层的厚度减小至类似于0.4 +/-0.1 ML，并完全消除了所有可检测的烃污染。随后在等离子体环境中的两个表面的冷却导致氧的化学吸附和从0.2 eV的向下带弯曲的样品在真空中冷却到0.3 eV的向上带弯曲的指示形成的耗尽层较低的表面电导率的变化。在任一环境中冷却产生化学计量的ZnO{0001}表面，其具有有序的晶体学以及在（000（1）棒上）表面上的台阶和平台微观结构;（0001）表面没有显著特征。顺序沉积的，未图案化的Au膜，并推测整流金接触，最初生长在两个表面上冷却的等离子体环境中通过形成的岛屿，随后合并，所示的计算从X-射线光电子能谱数据和确认的透射电子显微镜。根据最佳接触的电流-电压数据计算，发现（0001）[（000（1）条上）]表面上的势垒高度为0.71 +/- 0.05（0.60 +/- 0.05）eV，饱和电流密度为（4 +/- 0.5）X 10（-6）A/cm（2）（2.0 +/- 0.5 X 10（-4）A/cm（2）），较低值n=1.17 +/- 0.05（1.03 +/- 0.05），漏电流密度显著降低，接近1.0 X 10（-4）A/cm（2）（类似于91 × 10（-9）A/cm（2）），在8.5（7.0）V反向偏压之前，急剧，永久击穿（软击穿）。所有测得的势垒高度均低于预测的肖特基-莫特值1.0 eV，表明界面结构和相关的界面态影响肖特基势垒。然而，在连续原位沉积Au之前和之后，Zn 2 p（1.9 +/- 0.1 eV）和O 1 s（1.5 +/- 0.1 eV）的芯能级的半峰全宽的恒定性表明突然的未反应的Au/ZnO（0001）界面。透射电子显微镜证实了外延界面的非线性。将（0001）表面上的接触退火到80 5和150 5 ℃导致理想因子降低到1.12 +/- 0.05和1.09 +/- 0.05，饱和电流密度增加到9.05和4.34 μ A/cm（2），势垒高度分别为0.82 +/- 0.5和0.79 +/- 0.5 eV，漏电流密度分别为2 × 10（-3）A/cm（2）（6V）和20 × 10（-3）A/cm（2）（7V）。(c)2005年美国物理学会。
Current-voltage measurements of Au contacts deposited on ex situ cleaned, n-type ZnO(0001) [(000 (1) over bar)] surfaces showed reverse bias leakage current densities of similar to 0.01 (similar to 0.1) A/cm(2) at 4.6 (3.75) V reverse bias and ideality factors > 2 (both surfaces) before sharp, permanent breakdown (soft breakdown). This behavior was due primarily to the presence of (1.6-2.0)+/- 0.1 [(0.7-2.6)+/- 0.1] monolayers (ML) of hydroxide, which forms an electron accumulation layer and increases the surface conductivity. In situ remote plasma cleaning of the (0001) [(000 (1) over bar)] surfaces using a 20 vol % O-2/80 vol % He mixture for the optimized temperatures, times, and pressure of 550 +/- 20 degrees C (525 +/- 20 degrees C), 60 (30) min, and 0.050 Torr reduced the thickness of the hydroxide layer to similar to 0.4 +/- 0.1 ML and completely eliminated all detectable hydrocarbon contamination. Subsequent cooling of both surfaces in the plasma ambient resulted in the chemisorption of oxygen and a change from 0.2 eV of downward band bending for samples cooled in vacuum to 0.3 eV of upward band bending indicative of the formation of a depletion layer of lower surface conductivity. Cooling in either ambient produced stoichiometric ZnO{0001} surfaces having an ordered crystallography as well as a step-and-terrace microstructure on the (000 (1) over bar) surface; the (0001) surface was without distinctive features. Sequentially deposited, unpatterned Au films, and presumably the rectifying gold contacts, initially grew on both surfaces cooled in the plasma ambient via the formation of islands that subsequently coalesced, as indicated by calculations from x-ray photoelectron spectroscopy data and confirmed by transmission electron microscopy. Calculations from the current-voltage data of the best contacts revealed barrier heights on the (0001) [(000 (1) over bar)] surfaces of 0.71 +/- 0.05 (0.60 +/- 0.05) eV, a saturation current density of (4 +/- 0.5) X 10(-6) A/cm(2) (2.0 +/- 0.5 X 10(-4) A/cm(2)), a lower value of n=1.17 +/- 0.05 (1.03 +/- 0.05), a significantly lower leakage current density of similar to 1.0 X 10(-4) A/cm(2) (similar to 91 X 10(-9) A/cm(2)) at 8.5 (7.0) V reverse bias prior to sharp, permanent breakdown (soft breakdown). All measured barrier heights were lower than the predicted Schottky-Mott value of 1.0 eV, indicating that the interface structure and the associated interface states affect the Schottky barrier. However, the constancy in the full width at half maximum of the core levels for Zn 2p (1.9 +/- 0.1 eV) and O 1s (1.5 +/- 0.1 eV), before and after sequential in situ Au depositions, indicated an abrupt, unreacted Au/ZnO(0001) interface. Transmission electron microscopy confirmed the abruptness of an epitaxial interface. Annealing the contacts on the (0001) surface to 80 5 and 150 5 degrees C resulted in decreases in the ideality factors to 1.12 +/- 0.05 and 1.09 +/- 0.05 and increases in saturation current density to 9.05 and 4.34 mu A/cm(2), the barrier height to 0.82 +/- 0.5 and 0.79 +/- 0.5 eV, and in the leakage current densities to similar to 2 X 10(-3) A/cm(2) at6V and similar to 20 X 10(-3) A/cm(2) at 7 V, respectively. (c) 2005 American Institute of Physics.