Faraday-cage-assisted etching of suspended gallium nitride nanostructures - data

1. (a) Schematic of the cross section of the etch chamber containing the Faraday cage, with the GaN samples at its center, (b) schematic showing how ions directed at steep angles θ cause the characteristic undercut profile, (c) the plot of the predicted etch angles ϕ and θ, (d) a photograph of the triangular Faraday cage with a UK ten-pence coin for scale (diameter 24.5 mm), and (e) a scanning electron micrograph of a cleaved edge of a GaN waveguide sample etched in the cage to a depth 2d = 1.56 μm.

2. (a) Stripe etched without the cage, showing an etch angle of −15○, typical of ICP etched GaN, (b) an etch with the sample in a 45○ cage and with the same 1:1 Cl2:Ar gas mix, leading to a −22○ etch, and (c) an etch in a 45○ cage with a 5:1 Cl2:Ar mix to give a θ = 0○ etch profile.

3. (a) Free-standing singly clamped triangular cantilever 1 μm in width and 35 μm in length, suspended 2 μm above a planar layer, etched inside a Faraday cage with an equilateral triangular cross section and (b) a suspended doubly-clamped cantilever of 2 μm width.

4. Calculations of waveguides with an equilateral triangular cross-section: (a) the effective index of the waveguide modes (blue: TE and red: TM) as a function of the waveguide size (inset: the schematic of the calculation) and [(b) and (c)] the mode profiles for (b) the fundamental transverse electric mode and (c) the transverse magnetic mode. Addition profiles provide further information on the electric field.

Numerical values for construction of Figure 4(a) are provided.

Research results based upon these data are published at https://doi.org/10.1063/5.0007947