Direct observation of dopant distribution in GaAs compound semiconductors using phase-shifting electron holography and Lorentz microscopy

Sasaki, Hirokazu; Otomo, Shinya; Minato, Ryuichiro; Yamamoto, Kazuo; Hirayama, Tsukasa

doi:10.1093/jmicro/dfu008

Cited by 26 publications

(19 citation statements)

References 24 publications

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“…Fig. 3c shows the dopant concentration profiles of Zn and Si in p -type and n -type regions, respectively, obtained by secondary ion mass spectrometry (SIMS)16. In the p -type region, the DPC image intensity dip corresponds well to the boundary between the 10 18 and 10 19 atoms/cm3 doped regions (~200 nm off from the p-n junction).…”

Section: Resultsmentioning

confidence: 99%

“…This is expected, since smaller concentration steps will produce a smaller local electric field variation which leads to smaller electron beam deflections and thus requires still higher sensitivity to detect. In addition, it has been shown that the inactive layers become thicker in lower dopant concentration regions in the same GaAs semiconductor specimen16, which would also reduce the projected local electric field variation. This could be due to the large surface depletion layer formed during the FIB sample milling.…”

Section: Resultsmentioning

confidence: 99%

“…Fig. 4a also shows holography data for a very similar sample16. These data are noisier, because holography reconstructs the potential which must be differentiated to give the electric field profile.…”

Section: Discussionmentioning

confidence: 98%

“…Determining the electric field strength, the quantity of technological interest, is hampered because the measured total crystal thickness is not necessarily the active thickness: there may be inactive layers on the surfaces16. However, we can run the logic the other way, solving Poisson’s equations self-consistently based on the assumed dopant concentrations given in Fig.…”

Section: Discussionmentioning

confidence: 99%

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Imaging of built-in electric field at a p-n junction by scanning transmission electron microscopy

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Sasaki

et al. 2015

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Precise measurement and characterization of electrostatic potential structures and the concomitant electric fields at nanodimensions are essential to understand and control the properties of modern materials and devices. However, directly observing and measuring such local electric field information is still a major challenge in microscopy. Here, differential phase contrast imaging in scanning transmission electron microscopy with segmented type detector is used to image a p-n junction in a GaAs compound semiconductor. Differential phase contrast imaging is able to both clearly visualize and quantify the projected, built-in electric field in the p-n junction. The technique is further shown capable of sensitively detecting the electric field variations due to dopant concentration steps within both p-type and n-type regions. Through live differential phase contrast imaging, this technique can potentially be used to image the electromagnetic field structure of new materials and devices even under working conditions.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

Imaging of built-in electric field at a p-n junction by scanning transmission electron microscopy

Shibata

Findlay

Sasaki

et al. 2015

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Self Cite

125

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“…The sample was prepared by FIB, where the thickness of the sample was controlled to be about 200 nm. Detail information about this sample can be found elsewhere [5]. The same sample was characterized by DPC STEM in the previous study [6], where the inner electric field was clearly observed and analysed in a quantitative manner.…”

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Differential Phase Contrast Imaging with Reduced Dynamical Diffraction Effect

et al. 2017

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Phase contrast imaging in STEM has become a very exciting field after the rapid developments in segmented/pixel type detectors, and some powerful imaging techniques have been studied including Differential Phase Contrast (DPC) [1,2] and ptychography [3]. Particularly, DPC is a promising method for characterizing local internal electric and/or magnetic fields of functional materials (ex. magnet, semiconductor device) However, one of the most critical problems on the DPC imaging is artifact from diffraction contrast (ex. bend contours or equal thickness fringe): the acquired images of internal electric and/or magnetic field are severely disturbed by the waving background contrasts due to diffraction contrast. This is particularly critical when we perform DPC STEM for a sample along low index crystal axis at low magnification (that is, large field of view), where many diffracted beams are strongly excited and an intensity distribution of CBED patterns becomes highly complex, due to intensity exchanges between diffracted and direct beams, resulting in confusing image contrasts.To overcome such problems, we adopted the idea of Precession Electron Diffraction (PED) [4] into DPC STEM imaging to avoid these diffraction contrasts. The PED is known as a method for suppressing dynamical scattering effects in electron diffraction. Thus, we tried to apply the PED technique to DPC imaging ("precession DPC") to reduce diffraction contrast.A p-n junction in GaAs semiconductor was selected as a model sample. The sample was prepared by FIB, where the thickness of the sample was controlled to be about 200 nm. Detail information about this sample can be found elsewhere [5]. The same sample was characterized by DPC STEM in the previous study [6], where the inner electric field was clearly observed and analysed in a quantitative manner.The STEM observation results reported in this paper was performed using an aberration corrected microscope (JEOL, JEM-ARM200F) equipped with an 8-segmented STEM detector (JEOL, SAAF Octa). The optical condition for DPC STEM was set to be high sensitivity mode (STEM low-mag, incident angle ~ 150 μrad, effective camera length ~ 4000 cm). The DPC signals were calculated from the second layer of SAAF Octa detector (signals from channel 5~8).In the experiment, the GaAs [110] zone axis was aligned along the optic axis, and DPC images were acquired with and without precession control. In the former case, the optical system was fixed, and the relative angles between the incident beam and the specimen were manually controlled by X/Y tilt of the specimen holder. The range of precession angle was ± 0.5 degree for X and Y directions around the [110] axis, where the tilting step was set to be about 0.1 degree. A set of raw images was acquired for each step, so that we got 11×11 = 121 data sets from the same sample region. These sequential images were aligned by cross correlation processes, stacked and averaged into single data set, and then used for calculating the "precession DPC" image. For reference, a DPC imag...

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Analysis of GaAs compound semiconductors and the semiconductor laser diode using electron holography, Lorentz microscopy, electron diffraction microscopy and differential phase contrast STEM

Sasaki

Otomo

Minato

et al. 2016

European Microscopy Congress 2016: Proceedings

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In order to develop and manufacture semiconductor devices which are key components of the optical telecommunication products, such as the semiconductor laser diode, it is essential to confirm whether it is manufactured as designed. Electric potential distributions of the semiconductor devices are designed in nanoscale, so two dimensional methods to evaluate the electrical potential in the semiconductors with a high spatial resolution are necessary for product management. The observation of the gallium arsenide (GaAs) model specimen was carried out by using the electron holography and Lorentz microscopy [1]. Lorentz images and intensity profiles are shown in FIG 1 (a)‐(f). The p‐n junctions are clearly seen in both the 0.6 mm under‐focused and over‐focused images, but hardly any interfaces of different dopant concentration can be observed in the images. FIG 2 shows the electron holographic reconstructed phase image. The p‐ and n‐type regions are clearly seen as areas of dark and bright contrast, and some differences in the changing dopant concentrations can also be seen. A phase image of semiconductor laser diode by the electron holography is shown in FIG 3 [2]. In FIG 3(a), the interface region is approximately 5 μm. And the spacing between interface fringes is approximately 30 nm. Next, in order to observe the pn junction near the active layer in a high spatial resolution, the photograph was taken by changing the interference fringes conditions. The expanded phase image of a part of FIG 3(a), surrounded by a dotted line, is shown in FIG 3(b). Since the interference region is approximately 1.5 μm, and the interference fringe spacing is 5 nm, the spatial resolution is approximately 15 nm. As can be recognized from the phase image, we can understand that more detailed structure can be observed in the higher spatial resolution in comparison with the phase image in FIG 3(a). Here, the designed location of the pn junction was positioned at the dotted line, but it was found from the electron holography observation results that the pn junction did not exist in the original position. This semiconductor laser diode could not have the expected output characteristics. The structural defect of the pn junction, found out in this observation, is considered to be the cause. For other semiconductor electric voltage evaluation methods by TEM, electron diffraction microscopy [3] which is one method of phase reconstruction method, differential phase contrast [4] (DPC) which is one method of STEM are also effective and possible to be utilized complementarily with the electron holography. We will discuss about these methods applied for semiconductor in this presentation.

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Direct observation of dopant distribution in GaAs compound semiconductors using phase-shifting electron holography and Lorentz microscopy

Cited by 26 publications

References 24 publications

Imaging of built-in electric field at a p-n junction by scanning transmission electron microscopy

Imaging of built-in electric field at a p-n junction by scanning transmission electron microscopy

Differential Phase Contrast Imaging with Reduced Dynamical Diffraction Effect

Analysis of GaAs compound semiconductors and the semiconductor laser diode using electron holography, Lorentz microscopy, electron diffraction microscopy and differential phase contrast STEM

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