Band-Gap Deformation Potential and Elasticity Limit of Semiconductor Free-Standing Nanorods Characterized <i>in Situ</i> by Scanning Electron Microscope–Cathodoluminescence Nanospectroscopy

Modern field-effect transistors or laser diodes take advantages of band-edge structures engineered by large uniaxial strain ε_<i>zz</i>, available up to an elasticity limit at a rate of band-gap deformation potential <i>a</i>_<i>zz</i> (= d<i>E</i>_g/dε_<i>zz</i>). However, contrary to <i>a</i>_P values under hydrostatic pressure, there is no quantitative consensus on <i>a</i>_<i>zz</i> values under uniaxial tensile, compressive, and bending stress. This makes band-edge engineering inefficient. Here we propose SEM–cathodoluminescence nanospectroscopy under <i>in situ</i> nanomanipulation (Nanoprobe-CL). An apex of a <i>c</i>-axis-oriented free-standing ZnO nanorod (NR) is deflected by point-loading of bending stress, where local uniaxial strain (ε_<i>cc</i> = <i>r</i>/<i>R</i>) and its gradient across a NR (d<i>ε</i>_<i>cc</i>/d<i>r</i> = <i>R</i>^–1) are controlled by a NR local curvature (<i>R</i>^–1). The NR elasticity limit is evaluated sequentially (ε_<i>cc</i> = 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 <i>E</i>_g is evaluated from near-band-edge CL emission energy. Uniaxial <i>a</i>_<i>cc</i> (= d<i>E</i>_g/dε_<i>cc</i>) is evaluated at regulated surface depth, and the impact of <i>R</i>^–1 on observed <i>a</i>_<i>cc</i> is investigated. The <i>a</i>_<i>cc</i> converges with −1.7 eV to the <i>R</i>^–1 = 0 limit, whereas it quenches with increasing <i>R</i>^–1, which is attributed to free-exciton drift under transversal band-gap gradient. Surface-sensitive CL measurements suggest that a discrepancy from bulk <i>a</i>_<i>cc</i> = −4 eV may originate from strain relaxation at the side surface under uniaxial stress. The nanoprobe-CL technique reveals an <i>E</i>_g(ε_<i>ij</i>) response to specific strain tensor ε_<i>ij</i> (<i>i</i>, <i>j</i> = <i>x</i>, <i>y</i>, <i>z</i>) and strain-gradient effects on a minority carrier population, enabling simulations and strain-dependent measurements of nanodevices with various structures