Band-gap deformation potential and elasticity limit of semiconductor free-standing nanorods characterized in situ by scanning electron microscope-cathodoluminescence nanospectroscopy

Kentaro Watanabe, Takahiro Nagata, Yutaka Wakayama, Takashi Sekiguchi, Róbert Erdélyi, János Volk

Research output: Contribution to journalArticlepeer-review

18 Citations (Scopus)

Abstract

Modern field-effect transistors or laser diodes take advantages of band-edge structures engineered by large uniaxial strain εzz, available up to an elasticity limit at a rate of band-gap deformation potential azz (= dEg/dεzz). However, contrary to aP values under hydrostatic pressure, there is no quantitative consensus on azz values under uniaxial tensile, compressive, and bending stress. This makes band-edge engineering inefficient. Here we propose SEM-cathodoluminescence nanospectroscopy under in situ nanomanipulation (Nanoprobe-CL). An apex of a c-Axis-oriented free-standing ZnO nanorod (NR) is deflected by point-loading of bending stress, where local uniaxial strain (εcc = r/R) and its gradient across a NR (dεcc/dr = R-1) are controlled by a NR local curvature (R-1). The NR elasticity limit is evaluated sequentially (εcc = 0.04) from SEM observation of a NR bending deformation cycle. An electron beam is focused on several spots crossing a bent NR, and at each spot the local Eg is evaluated from near-band-edge CL emission energy. Uniaxial acc (= dEg/dεcc) is evaluated at regulated surface depth, and the impact of R-1 on observed acc is investigated. The acc converges with -1.7 eV to the R-1 = 0 limit, whereas it quenches with increasing R-1, which is attributed to free-exciton drift under transversal band-gap gradient. Surface-sensitive CL measurements suggest that a discrepancy from bulk acc = -4 eV may originate from strain relaxation at the side surface under uniaxial stress. The nanoprobe-CL technique reveals an Egij) response to specific strain tensor εij (i, j = x, y, z) and strain-gradient effects on a minority carrier population, enabling simulations and strain-dependent measurements of nanodevices with various structures.

Original languageEnglish
Pages (from-to)2989-3001
Number of pages13
JournalACS Nano
Volume9
Issue number3
DOIs
Publication statusPublished - 2015 Mar 24
Externally publishedYes

Keywords

  • ZnO
  • cathodoluminescence
  • deformation potential
  • free-standing nanowire
  • in-situ scanning electron microscopy
  • plastic deformation
  • surface elasticity

ASJC Scopus subject areas

  • Materials Science(all)
  • Engineering(all)
  • Physics and Astronomy(all)

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