Study of ordinary facets revealed in (1 0 0) InP by etching in HCl

We studied the tilt, curvature and surface morphology of side facets of mesa ridges revealed in (1 0 0) InP by etching in 3HCl (37%):1H3PO4 (85%) through InGaAs mask. The ridges lay at variable angle ω ∈ [45.5°; 90°] to [0 1 1] within the sector between [0 0 1] and [0 1¯ 1]. For each ω, a unique ridge shape was exposed defined at each of its long sides by a single positively sloped facet.Ridges with ω = 45.5° were confined to facets tilted at α ∼ 45°, related to {1 1 0} planes. The facets were straight and very smooth with a root-mean-square roughness σ as low as 0.9 nm. The other ridges had more moderately sloped facets: as ω increased, their tilt gradually decreased to α ∼ 35° at ω = 90°. While the facets with ω < 50° were very smooth and straight, the ones with 50° ≤ ω ≤ 90° were rougher, striated and increasingly curved.The roughness of the facet surfaces was associated with the striations and was explained as follows: during the etching in 3HCl:1H3PO4, relative fluctuations along edges of the InGaAs mask (line-edge roughness—LER) were transferred as striations onto the ridge facets. The transfer was markedly suppressed for the facets with 45.5° ≤ ω < 50° because the LER was quickly undercut as fast etching micro- and nano-sized facets were exposed at such orientations. By contrast, slowly etching or etch-stop micro- and nano-sized facets were revealed under the fluctuations for the ridges at 50° ≤ ω ≤ 90°. The undercutting of the LER was consequently suppressed, and the ridge facets were formed striated and rougher.