Semiconductor device and method of fabricating the same

A method of fabricating a semiconductor device, comprising:

• providing a substrate, the substrate being formed with a locating notch in an edge thereof, wherein a line connecting a center of the substrate and the locating notch defines a reference direction, wherein across a surface of the substrate, regions oriented in first and second crystallographic directions belonging to different families of crystallographic directions are periodically distributed around the center, and wherein the reference direction is parallel to the first crystallographic direction or the second crystallographic direction;
• forming a patterned mask layer on the surface of the substrate, the patterned mask layer defining a pattern distributed in parallel to the first crystallographic direction;
• and
• forming a plurality of trenches by performing a wet etching process on the surface of the substrate using the patterned mask layer as a mask, the plurality of trenches each having a cross-sectional width decreasing from the surface of the substrate to the inside of the substrate, when viewed normal to a cross-section perpendicular to the substrate, and the plurality of trenches forming a finely roughened surface structure for extending an optical path length in an optoelectronic device,
• wherein the patterned mask layer comprises a first set of elongate pattern elements and a second set of elongate pattern elements, and wherein the second set of elongate pattern elements is arranged on both sides of the first set of elongate pattern elements, or the first set of elongate pattern elements is arranged on both sides of the second set of elongate pattern elements,
• wherein the wet etching process employs at least one of a tetramethyl ammonium hydroxide (TMAH) solution, an ammonia solution, a potassium hydroxide (KOH) solution and a sodium hydroxide (NaOH) solution, and
• wherein the plurality of trenches are at least one of inverted quadrilateral pyramid-shaped trenches and inverted truncated quadrilateral pyramid-shaped trenches.