In-situ biasing and temperature influence on the electric fields across GaAs based p-n junction via 4D STEM

Session

Stream 1: EMAG - 4D-STEM

Authors

Dr. Anuj Pokle (1), Mr. Damien Heimes (1), Dr. Andreas Beyer (1), Prof. Kerstin Volz (1)

Affiliations

1. Philipps University Marburg

Keywords

In-situ biasing, cryo, p-n junction, electric field measurements, FIB, 4D STEM and COM

Abstract text

The ability to determine electric fields at the nanoscale quantitatively is critical for understanding semiconductor device properties. By employing transmission electron microscopy techniques like electron holography and differential phase-contrast imaging (DPC), fundamental aspects of the electron interaction with the electric potential field have been investigated ^1,2. By performing in situ biasing, the effect of external voltages on GaAs and Si p-n junctions have also been investigated with electron holography ^3,4. However, this approach requires a specialized setup where the primary beam is split into two, wherein the reference wave later interacts with the second wave passing via the specimen. 

Nevertheless, in recent times accessibility to direct electron detectors has enabled us to acquire four-dimensional datasets (diffraction patterns at each scan point), paving the way for new advanced developments. Here we combine in-situ biasing with a four-dimensional scanning transmission electron microscopy (4DSTEM) technique to study the influence on the depletion region in the GaAs-based p-n junction. In addition, the temperature influence on the electric fields is also investigated at liquid nitrogen temperature (~ -183 °C) to above room temperature (~50 °C). The biasing and temperature-dependent studies are conducted by incorporating an in situ biasing and a cryo holder, respectively. 

In this study, the momentum transfer induced by internal electric fields is measured by the diffraction pattern's center-of-mass (COM) shift ⁵. Identical imaging conditions are employed, which are used for obtaining high-resolution STEM images. Moreover, our sample preparation approach is based on the focused ion beam (FIB) method, which is nontrivial from the perspective of placing the lamella on the biasing MEMS chip. This enables us to determine the electrical properties for a known sample thickness observed from both biased and unbiased junctions followed by temperature application. Here we will show the biasing and temperature influence's critical characteristic on the depletion region width. 

References

1. Shibata, N. et al. Imaging of built-in electric field at a p-n junction by scanning transmission electron microscopy. Sci Rep 5, (2015).

2. McCartney, M. R., Dunin-Borkowski, R. E. & Smith, D. J. Quantitative measurement of nanoscale electrostatic potentials and charges using off-axis electron holography: Developments and opportunities. Ultramicroscopy 203, 105–118 (2019).

3. Twitchett, A. C., Dunin-Borkowski, R. E. & Midgley, P. A. Quantitative Electron Holography of Biased Semiconductor Devices. PHYSICAL REVIEW LETTERS 88, 4 (2002).

4. Anada, S. et al. Precise measurement of electric potential, field, and charge density profiles across a biased GaAs p-n tunnel junction by in situ phase-shifting electron holography. Journal of Applied Physics 122, 225702 (2017).

5. Beyer, A. et al. Quantitative Characterization of Nanometer-Scale Electric Fields via Momentum-Resolved STEM. Nano Lett. (2021) doi:10.1021/acs.nanolett.0c04544.