Visualization of different carrier concentrations in n-type-GaN semiconductors by phase-shifting electron holography with multiple electron biprisms
Visualization of different carrier concentrations in n-type-GaN semiconductors by phase-shifting electron holography with multiple electron biprisms
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通过多电子双棱镜相移电子全息术可视化 n 型 GaN 半导体中的不同载流子浓度
DOI：
10.1093/jmicro/dfz037
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发表时间：
2019
期刊：
影响因子：
1.8
通讯作者：
Hirayama Tsukasa
中科院分区：
文献类型：
--
作者：
Yamamoto Kazuo;Nakano Kiyotaka;Tanaka Atsushi;Honda Yoshio;Ando Yuto;Ogura Masaya;Matsumoto Miko;Anada Satoshi;Ishikawa Yukari;Amano Hiroshi;Hirayama Tsukasa
使用透射电子显微镜（TEM）进行的相移电子全息术（PS-EH）被应用于可视化具有不同浓度的被Si激活的载流子的层（掺杂剂水平为1019、1018、1017和1016原子cm-3）In型GaN半导体。为了精确测量GaN样品中的重构相位分布，使用三个电子双棱镜获得了一系列没有双棱镜灯丝产生的菲涅耳条纹的高对比度全息图，并使用低温聚焦离子束（cryo-FIB）制备了在宽视场中具有较小畸变的均匀TEM样品。350 nm厚的TEM样品中的所有层以1.8 nm的空间分辨率和0.02 rad的相位分辨率区分，并且还测量了层之间的界面处的相位分布中的台阶宽度（对应于耗尽宽度）的变化。在每个掺杂剂水平的活性和非活性层的厚度估计从观察到的相位分布和理论能带结构的模拟。随着掺杂剂浓度的降低，TEM样品的有源层厚度与总厚度之比显著降低;因此，需要更厚的TEM样品来观察更低的载流子浓度;例如，区分掺杂剂浓度为1016和1015原子cm-3的层。据估计，样品厚度必须大于700 nm，才有可能通过PS-EH和cryo-FIB的组合来检测亚层。
Phase-shifting electron holography (PS-EH) using a transmission electron microscope (TEM) was applied to visualize layers with different concentrations of carriers activated by Si (at dopant levels of 1019, 1018, 1017and 1016atoms cm−3) inn-type GaN semiconductors. To precisely measure the reconstructed phase profiles in the GaN sample, three electron biprisms were used to obtain a series of high-contrast holograms without Fresnel fringes generated by a biprism filament, and a cryo-focused-ion-beam (cryo-FIB) was used to prepare a uniform TEM sample with less distortion in the wide field of view. All layers in a 350-nm-thick TEM sample were distinguished with 1.8-nm spatial resolution and 0.02-rad phase-resolution, and variations of step width in the phase profile (corresponding to depletion width) at the interfaces between the layers were also measured. Thicknesses of the active and inactive layers at each dopant level were estimated from the observed phase profile and the simulation of theoretical band structure. Ratio of active-layer thickness to total thickness of the TEM sample significantly decreased as dopant concentration decreased; thus, a thicker TEM sample is necessary to visualize lower carrier concentrations; for example, to distinguish layers with dopant concentrations of 1016and 1015atoms cm−3. It was estimated that sample thickness must be more than 700 nm to make it be possible to detect sub-layers by the combination of PS-EH and cryo-FIB.