The morphology of etch pits on a sapphire surface

Tridimensional morphology and kinetics of etch pit on the {0001} plane of sapphire crystal

“…The hexagonal etch pit shows a cross section with three groups of parallel edges along directions [1 1 2 0], [2 1 1 0] and [1 2 1 0], the lengths of two edges in every group are different, but the lengths of the long edges as well as the lengths of the short edges are equal. These observations are consistent with the results obtained by Liu et al [3].…”

“…At atomic scale, the edges of an etch pit on the etching surface were regarded to be composed by the oxygen atoms in directions [1 1 2 0], [2 1 1 0] and [1 2 1 0] [3]. In our opinion, the C-{0 0 0 1} plane of sapphire crystal could be classified into two kinds of planes, namely oxygen atomic plane and aluminium atomic plane since sapphire crystal (Fig.…”

“…Up to now, triangular [1,3,8,11], hexagonal [1,3,8] and quadrilateral [1] etch pits have been observed on C-plane {0 0 0 1} of sapphire. On A-plane {1 1 2 0}, only rhombic pyramidal etch pits were observed [3,10]. On the plane {1 0 1 1}, the etch pits are triangular or rhombic, and hexagonal on plane {1 1 0 0} [8].…”

“…However, crystalline defects like dislocation, stack fault would intensely worsen the properties of sapphire. Thus, the characterisation of crystalline defects has become increasingly important [3], leading to the renaissance of wet etch method.…”

“…They pointed out that only a few etchants can be used to develop pits at dislocation sits under high temperature for the high resistance of sapphire to chemical attack [3]. Those etchants are phosphoric acid (H 3 PO 4 ) [9], potassium bisulphate (KHSO 4 ) [10], borax (Na 2 B 4 O 7 ) [3,11], potassium hydroxide (KOH) [11] and 15%HClþ 15%HNO 3 þH 2 O [1].…”