Various embodiments provide thin-walled structures and methodologies for their formation. In one embodiment, the thin-walled structure can be formed by disposing a semiconductor material in a patterned aperture using a selective growth mask that includes a plurality of patterned apertures, followed by a continuous growth of the semiconductor material using a pulsed growth mode. The patterned aperture can include at least one lateral dimension that is small enough to allow a threading defect termination at sidewall(s) of the formed thin-walled structure. In addition, high-quality III-N substrate structures and core-shell MQW active structures can be formed from the thin-walled structures for use in devices like light emitting diodes (LEDs), lasers, or high electron mobility transistors (HEMTs).