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Multistep staircase avalanche photodiodes with extremely low noise and deterministic amplification


In 1982, Capasso and co-workers proposed the solid-state analogue of the photomultiplier tube, termed the staircase avalanche photodiode. Through a combination of compositional grading and small applied bias, the conduction band profile is arranged into a series of steps that function similar to the dynodes of a photomultiplier tube, with twofold gain arising at each step via impact ionization. A single-step staircase was previously reported but did not demonstrate gain scaling through cascading multiple steps or report noise properties. Here we demonstrate gain scaling of up to three steps; measurements show the expected 2N scaling with the number of staircase steps, N. Furthermore, measured noise increased more slowly with gain than for photomultiplier tubes, probably due to the lower stochasticity of impact ionization across well-designed heterojunctions as compared with the secondary electron emission from metals. Excellent agreement was found between the experiments and Monte Carlo simulations for both gain and noise.

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Fig. 1: A structural comparison of a low-noise PMT and multistep staircase APD.
Fig. 2: Staircase APD design used to produce localized, single-carrier 2N gain.
Fig. 3: Demonstration of deterministic 2N gain scaling.
Fig. 4: Calculated staircase APD impact ionization probability and excess noise factors.
Fig. 5: Measured and modelled staircase APD noise benefit at 300 K.
Fig. 6: Estimated SNR comparison between staircase and conventional APDs in the shot-noise limit.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author on reasonable request. Source data are provided with this paper.

Code availability

Simulation software used to produce electrostatic models are available at the following GitHub repository:


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This work was supported by the Army Research Office and DARPA (contract no. W911NF-17-1-0065) and DARPA (contract no. W909MY-12-D-0008). We acknowledge use of Texas Nanofabrication Facilities supported by the NSF NNCI Award 1542159.

Author information




S.D.M. and S.R.B. carried out simulations, crystal growth and materials characterization. A.H.J. and J.C.C. were responsible for device fabrication and experimental characterization. Analysis was performed by S.D.M. and A.H.J. S.D.M. and A.H.J. wrote the paper with assistance from J.C.C. and S.R.B. S.D.M., A.H.J., J.C.C. and SRB all contributed to the structure design.

Corresponding authors

Correspondence to Stephen D. March or Seth R. Bank.

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The authors declare no competing interests.

Additional information

Peer review information Nature Photonics thanks M. Saif Islam and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figs. 1–8 and Discussion.

Source data

Source Data Fig. 2

Impact ionization, band diagrams, gain distributions, source data.

Source Data Fig. 3

Measured and simulated staircase gain.

Source Data Fig. 4

Fit-to-measured staircase gain and excess noise.

Source Data Fig. 5

Staircase excess noise compared to conventional APDs and PMTs.

Source Data Fig. 6

Estimated SNR performance comparing staircase APD to conventional APDs.

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March, S.D., Jones, A.H., Campbell, J.C. et al. Multistep staircase avalanche photodiodes with extremely low noise and deterministic amplification. Nat. Photonics 15, 468–474 (2021).

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