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Perez C, Ellis SR, Alcorn FM, Smoll EJ, Fuller EJ, Leonard F, Chandler D, Talin AA, Bisht RS, Ramanathan S, Goodson KE, Kumar S. Picosecond carrier dynamics in InAs and GaAs revealed by ultrafast electron microscopy. SCIENCE ADVANCES 2024; 10:eadn8980. [PMID: 38748793 PMCID: PMC11095486 DOI: 10.1126/sciadv.adn8980] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/05/2024] [Accepted: 04/10/2024] [Indexed: 05/19/2024]
Abstract
Understanding the limits of spatiotemporal carrier dynamics, especially in III-V semiconductors, is key to designing ultrafast and ultrasmall optoelectronic components. However, identifying such limits and the properties controlling them has been elusive. Here, using scanning ultrafast electron microscopy, in bulk n-GaAs and p-InAs, we simultaneously measure picosecond carrier dynamics along with three related quantities: subsurface band bending, above-surface vacuum potentials, and surface trap densities. We make two unexpected observations. First, we uncover a negative-time contrast in secondary electrons resulting from an interplay among these quantities. Second, despite dopant concentrations and surface state densities differing by many orders of magnitude between the two materials, their carrier dynamics, measured by photoexcited band bending and filling of surface states, occur at a seemingly common timescale of about 100 ps. This observation may indicate fundamental kinetic limits tied to a multitude of material and surface properties of optoelectronic III-V semiconductors and highlights the need for techniques that simultaneously measure electro-optical kinetic properties.
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Affiliation(s)
- Christopher Perez
- Sandia National Laboratories, Livermore, CA, USA
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - Scott R. Ellis
- Sandia National Laboratories, Livermore, CA, USA
- Intel Corporation, San Jose, CA, USA
| | | | | | | | | | | | | | - Ravindra Singh Bisht
- Department of Electrical and Computer Engineering, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
| | - Shriram Ramanathan
- Department of Electrical and Computer Engineering, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
| | - Kenneth E. Goodson
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - Suhas Kumar
- Sandia National Laboratories, Livermore, CA, USA
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Tian Y, Yang D, Ma Y, Li Z, Li J, Deng Z, Tian H, Yang H, Sun S, Li J. Spatiotemporal Visualization of Photogenerated Carriers on an Avalanche Photodiode Surface Using Ultrafast Scanning Electron Microscopy. NANOMATERIALS (BASEL, SWITZERLAND) 2024; 14:310. [PMID: 38334581 PMCID: PMC10857202 DOI: 10.3390/nano14030310] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Revised: 01/25/2024] [Accepted: 01/30/2024] [Indexed: 02/10/2024]
Abstract
The spatiotemporal evolution of photogenerated charge carriers on surfaces and at interfaces of photoactive materials is an important issue for understanding fundamental physical processes in optoelectronic devices and advanced materials. Conventional optical probe-based microscopes that provide indirect information about the dynamic behavior of photogenerated carriers are inherently limited by their poor spatial resolution and large penetration depth. Herein, we develop an ultrafast scanning electron microscope (USEM) with a planar emitter. The photoelectrons per pulse in this USEM can be two orders of magnitude higher than that of a tip emitter, allowing the capture of high-resolution spatiotemporal images. We used the contrast change of the USEM to examine the dynamic nature of surface carriers in an InGaAs/InP avalanche photodiode (APD) after femtosecond laser excitation. It was observed that the photogenerated carriers showed notable longitudinal drift, lateral diffusion, and carrier recombination associated with the presence of photovoltaic potential at the surface. This work demonstrates an in situ multiphysics USEM platform with the capability to stroboscopically record carrier dynamics in space and time.
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Affiliation(s)
- Yuan Tian
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Dong Yang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yu Ma
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Zhongwen Li
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
| | - Jun Li
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
| | - Zhen Deng
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
| | - Huanfang Tian
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
| | - Huaixin Yang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Shuaishuai Sun
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
- Songshan Lake Materials Laboratory, Dongguan 523808, China
| | - Jianqi Li
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
- Songshan Lake Materials Laboratory, Dongguan 523808, China
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Garming MWH, Kruit P, Hoogenboom JP. Imaging resonant micro-cantilever movement with ultrafast scanning electron microscopy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2022; 93:093702. [PMID: 36182522 DOI: 10.1063/5.0089086] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Accepted: 08/11/2022] [Indexed: 06/16/2023]
Abstract
Here, we demonstrate ultrafast scanning electron microscopy (SEM) for making ultrafast movies of mechanical oscillators at resonance with nanoscale spatiotemporal resolution. Locking the laser excitation pulse sequence to the electron probe pulses allows for video framerates over 50 MHz, well above the detector bandwidth, while maintaining the electron beam resolution and depth of focus. The pulsed laser excitation is tuned to the oscillator resonance with a pulse frequency modulation scheme. We use an atomic force microscope cantilever as a model resonator, for which we show ultrafast real-space imaging of the first and even the 2 MHz second harmonic oscillation as well as verification of power and frequency response via the ultrafast movies series. We detect oscillation amplitudes as small as 20 nm and as large as 9 μm. Our implementation of ultrafast SEM for visualizing nanoscale oscillatory dynamics adds temporal resolution to the domain of SEM, providing new avenues for the characterization and development of devices based on micro- and nanoscale resonant motion.
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Affiliation(s)
- Mathijs W H Garming
- Department of Imaging Physics, Delft University of Technology, Delft, The Netherlands
| | - Pieter Kruit
- Department of Imaging Physics, Delft University of Technology, Delft, The Netherlands
| | - Jacob P Hoogenboom
- Department of Imaging Physics, Delft University of Technology, Delft, The Netherlands
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Morishita H, Ohshima T, Otsuga K, Kuwahara M, Agemura T, Ose Y. Brightness evaluation of pulsed electron gun using negative electron affinity photocathode developed for time-resolved measurement using scanning electron microscope. Ultramicroscopy 2021; 230:113386. [PMID: 34534748 DOI: 10.1016/j.ultramic.2021.113386] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Revised: 08/14/2021] [Accepted: 08/23/2021] [Indexed: 10/20/2022]
Abstract
Temporal changes in carrier relaxations, magnetic switching, and biological structures are known to be in the order of ns. These phenomena can be typically measured by means of an optical-pump & electron-probe method using an electron microscope combined with a pulsed electron source. A photoemission-type pulsed electron gun makes it possible to obtain a short-pulsed electron beam required for high temporal resolution. On the other hand, spatial resolution is restricted by the brightness of the pulsed electron gun used in electron microscopes when a low brightness electron source is used and an irradiation current larger than a certain value is required. Thus, we constructed a prototype pulsed electron gun using a negative electron affinity (NEA) photocathode for time-resolved measurement using a scanning electron microscope (SEM) with high spatiotemporal resolution. In this study, a high-speed detector containing an avalanche photodiode (APD) was used to directly measure waveforms of the pulsed electron beam excited by a rectangular-shape pulsed light with a variable pulse duration in the range of several ns to several μs. The measured waveforms were the same rectangular shape as incident pulsed excitation light. The maximum peak brightness of the pulsed electron beam was 4.2×107 A/m2/sr/V with a pulse duration of 3 ns. This value was larger than that of the continuous electron beam (1.6 × 107 A/m2/sr/V). Furthermore, an SEM image with image sharpness of 6.2 nm was obtained using an SEM equipped with a prototype pulsed electron gun at an acceleration voltage of 3 kV.
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Affiliation(s)
- Hideo Morishita
- Research & Development Group, Hitachi, Ltd., 1-280, Higashi-koigakubo Kokubunji-shi, Tokyo 185-8601, Japan; Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya-shi, Aichi 464-8603, Japan.
| | - Takashi Ohshima
- Research & Development Group, Hitachi, Ltd., 1-280, Higashi-koigakubo Kokubunji-shi, Tokyo 185-8601, Japan
| | - Kazuo Otsuga
- Research & Development Group, Hitachi, Ltd., 1-280, Higashi-koigakubo Kokubunji-shi, Tokyo 185-8601, Japan
| | - Makoto Kuwahara
- Institute of Materials and Systems for Sustainability, Nagoya University, Furo-cho, Chikusa-ku, Nagoya-shi, Aichi 464-8603, Japan
| | - Toshihide Agemura
- Hitachi High-Tech Corporation, 882, Ichige, Hitachinaka-shi, Ibaraki 312-8504, Japan
| | - Yoichi Ose
- Hitachi High-Tech Corporation, 882, Ichige, Hitachinaka-shi, Ibaraki 312-8504, Japan
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Zaghloul M, Pietralunga SM, Irde G, Sala V, Cerullo G, Chen H, Isella G, Lanzani G, Zani M, Tagliaferri A. Dynamical imaging of local photovoltage at semiconductor surface by photo-assisted ultrafast scanning electron microscopy. EPJ WEB OF CONFERENCES 2021. [DOI: 10.1051/epjconf/202125511001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Photo-assisted Ultrafast Scanning Electron Microscopy (USEM) maps the dynamics of surface photovoltages and local electric fields in semiconducting samples. Photovoltages and their gradients close to surface affect the emission yield and the detection efficiency of secondary electrons (SE), leading to photoexcited SE 2D patterns. In this work, we present a method to characterize the evolution of the patterns up to ultrafast regime. These results reveal the role of surface states in affecting the external field dynamics at picoseconds. Moreover, we show that tiny changes in surface preparation express deeply different photoexcited voltage signals. We investigate the relation between the surface chemistry of Si and photo-induced SE contrast.
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