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Deep Elastic Strain Engineering of Free-Standing GaN Microbridge

Sufeng Fan1,2,3,*, Heyi Wang1,*, Chang-Ti Chou4,*, Juzheng Chen1,5, Ying Han2, Jingzhuo Zhou1, Xiaocui Li2,6, Jyh-Pin Chou7,†, Ju Li8,‡ et al.

Yang Lu1,9,§

  • *These authors contributed equally to this work.
  • †Contact author: jpchou@ntu.edu.tw
  • ‡Contact author: liju@mit.edu
  • §Contact author: ylu1@hku.hk
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Phys. Rev. X 16, 011014 – Published 23 January, 2026

DOI: https://doi.org/10.1103/x76f-2vj8

Abstract

Gallium nitride (GaN) as a direct band gap semiconductor played a central role in the historical development of efficient blue light-emitting diode and laser diode, in which its intrinsic wide band gap shrinks through the addition of indium (In), thus tuning the color of the light by changing the chemistry. This alloying approach, however, does not allow for dynamic and reversible modulation of the band gap and emission color. Here we show that ultralarge tensile elastic strain can be introduced in microfabricated single crystal GaN microbridges and offer an unprecedented opportunity to modulate its band structure and optoelectronic properties continuously through deep elastic strain engineering. The elastic strain-induced energy band gap modulation was characterized and quantified by in situ cathodoluminescence (CL) as well as via strained GaN devices inside a scanning electron microscope. The CL emission of deeply strained (>5%) GaN microbridges has shown substantial band gap reduction from ∼3.4 to 2.96 eV (∼365 to 420 nm in wavelength), making its optical emission shift from invisible or UV to the blue visible regime. Experimental results agree well with ab initio calculation of the change in band gap with increased strain. This dynamic, reversible, and well-controllable strain engineering would facilitate novel device applications in power electronics and optoelectronics.

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Popular Summary

One critical step toward the historical breakthrough in developing an efficient blue light-emitting diode (LED) was achieved by shrinking the band gap through the addition of indium into the gallium nitride (GaN) active layer. However, such chemical alloying changes the material’s optoelectronic properties permanently, preventing dynamic and reversible tuning possibilities. We demonstrate a mechanical alternative to chemical doping. By tensile elastic straining of microfabricated GaN, we can continuously and reversibly shift pristine GaN band gap emission from the intrinsic ultraviolet (∼3.4 eV) to a visible blue light regime (down to 2.96 eV). This emission of about 420 nm is comparable to chemically alloyed blue LEDs. We further design and demonstrate strain-fixed GaN with effective band gap modulation as proof of concept for potential “strained GaN” device applications. In light of the current importance of GaN in the wide-band-gap semiconductor industry, deep elastic strain engineering could push power electronics, radio frequency communications, and optoelectronics technologies into interesting directions.

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Phys. Rev. X 16, 011014– Published 23 January, 2026
  • Received 30 August 2025
  • Accepted 2 January 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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