Impact ionization, which supports carrier multiplication, is promising for applications in single photon detection1 and sharp threshold swing field effect devices2. However, initiating the impact ionization of avalanche breakdown requires a high applied electric field in a long active region, which hampers carrier multiplication with a high gain, low bias and superior noise performance3,4. Here we report the observation of ballistic avalanche phenomena in sub-mean free path (MFP) scaled vertical InSe/black phosphorus (BP)5,6,7,8,9 heterostructures10. We use these heterojunctions to fabricate avalanche photodetectors (APDs) with a sensitive mid-infrared light detection (4 μm wavelength) and impact ionization transistors with a steep subthreshold swing (<0.25 mV dec–1). The devices show a low avalanche threshold (<1 V), low noise figure and distinctive density spectral shape. Our transport measurements suggest that the breakdown originates from a ballistic avalanche phenomenon, where the sub-MFP BP channel support the lattice impact ionization by electrons and holes and the abrupt current amplification without scattering from the obstacles in a deterministic nature. Our results provide new strategies for the development of advanced photodetectors1,11,12 via efficient carrier manipulation at the nanoscale.

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This project was primarily supported by the National Key Basic Research Program of China (grant nos 2018YFA0307200, 2015CB921600, 2013CBA01603 and 2018YFA0209100), the National Natural Science Foundation of China (grant nos 61775092, 61625402, 61574076, 11374142, 11574136, 11534010, 91750109 and 61725505), the Key Research Program of Frontier Sciences CAS (grant no. QYZDY-SSW-SLH021), the State Key Laboratory of Precision Measurement Technology and Instruments Fund for open topics, the Fundamental Research Funds for the Central Universities and the Collaborative Innovation Centre of Advanced Microstructures.

Author information


  1. National Laboratory of Solid State Microstructures, School of Physics, School of Electronic Science and Engineering, Collaborative Innovation Centre of Advanced Microstructures, Nanjing University, Nanjing, China

    • Anyuan Gao
    • , Yaojia Wang
    • , Junwen Zeng
    • , Geliang Yu
    • , Tianjun Cao
    • , Feng Miao
    • , Yi Shi
    •  & Xiaomu Wang
  2. International Centre for Quantum Materials, School of Physics, Peking University, Beijing, China

    • Jiawei Lai
    •  & Dong Sun
  3. Materials Department, University of California, Santa Barbara, CA, USA

    • Zhen Zhu
  4. Hefei National Laboratory for Physical Science at Microscale and Department of Physics, University of Science and Technology of China, Hefei, China

    • Naizhou Wang
    •  & Xianhui Chen
  5. Key Laboratory of Strongly Coupled Quantum Matter Physics, University of Science and Technology of China, Hefei, China

    • Naizhou Wang
    •  & Xianhui Chen
  6. College of Information Science and Electronic Engineering, ZJU-UIUC Institute, Zhejiang University, Haining, China

    • Wenchao Chen
  7. State Key Laboratory of Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai, China

    • Weida Hu
  8. Collaborative Innovation Centre of Quantum Matter, Beijing, China

    • Dong Sun


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X.W., F.M. and A.G. conceived and designed the experiments. A.G. fabricated the devices. A.G., Y.W., J.Z., G.Y. and T.C. conducted the transport measurements. A.G., J.L., W.H. and D.S. conducted the photoresponse measurements. Z.Z. and W.C. performed the DFT calculations. N.W. and X.C. helped to grow the BP crystals. A.G., X.W. and F.M. analysed the data and wrote the manuscript. X.W., F.M. and Y.S. supervised the research. All the authors discussed the obtained results.

Competing interests

The authors declare no competing interests.

Corresponding authors

Correspondence to Feng Miao or Yi Shi or Xiaomu Wang.

Supplementary information

  1. Supplementary information

    Observation of ballistic avalanche phenomena in nanoscale vertical InSe/BP heterostructures

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