Thickness dependent field emission study of LaB₆ coated Si nanowire arrays

A simple physical metal mask is efficiently employed to obtain an array of silicon (Si) nanowires (Si-NWs) on a Si substrate grown using the hot filament chemical vapor deposition route. Well adhered and uniform coating of different thicknesses (20 and 50 nm) of lanthanum hexaboride (LaB₆) on Si-NWs was obtained using electron beam evaporation technique. The thickness of LaB₆ coating was estimated from ellipsometry measurement. Structural, morphological, and chemical properties of the LaB₆ coated Si-NWs (LaB₆@Si-NWs) arrays were revealed using x-ray diffraction, field emission scanning electron microscope, transmission electron microscope, Raman spectroscopy, and x-ray photoelectron spectroscopy. Field electron emission characteristics of pristine Si-NW array and LaB₆ coated Si-NWs array emitters were studied in planar diode configuration at a base pressure of 1 × 10⁻⁸ mbar. The values of turn-on field (current density ∼1 μA/cm²) were observed as ∼2.2, 1.2, and 1.6 V/μm for pristine Si-NWs, LaB₆@Si-NWs_20, and LaB₆@Si-NWs_50 array emitters, respectively. Furthermore, maximum emission current densities of ∼1276.81, 2763.64, and 2231.81 μA/cm² have been extracted from the pristine Si-NWs, LaB₆@Si-NWS_20, and LaB₆@Si-NWS_50 array emitters at an applied field of 3.1, 2.7, and 2.7 V/μm, respectively. The LaB₆@Si-NWS_20 array emitter demonstrated superior FEE properties as compared to the pristine Si-NWs and LaB₆@Si-NWS_50 emitters. Furthermore, LaB₆@Si-NWS_20 emitter depicted very good emission current stability tested at a preset value of 1 μA over a duration of 3 h. The enhanced FEE performance exhibited by the LaB₆@Si-NWs_20 array emitter is attributed to reduction in effective work function and enhanced electron tunneling probability across the LaB₆–Si interface.