Researchers in Moldova have fabricated nanometre-thin membranes of gallium nitride for the first time and investigated their nanostructure using electron microscopy.
Uses of GaN
GaN is a large-bandgap semiconductor material which is biocompatible, piezoelectric and resistant to ionizing radiation. It is widely used in electronics applications such as high-temperature, high-power electronics, optoelectronics for light-emitting diodes, lasers and spintronics devices.
Etching GaN
Researchers have now developed a technique that involves etching away high-quality crystalline material from bulk GaN epilayers to leave behind only the dislocation networks and a thin film to which the dislocations remain attached. A modified version of the surface charge lithography (SCL) technique has been recently developed for pre-treating a semiconductor surface using a low-energy ion beam to induce trapped negative charges that then effectively shield the material against subsequent photoelectrochemical (PEC) etching. For example, low-fluence Ar ions with energies as low as 0.4 keV can be applied to the GaN surface to do just this. The material remains transparent to ultraviolet light, however, so it can still be deeply etched.
GaN nano-roof
Because threading dislocations survive PEC etching due to their negative charge, etching in potassium hydroxide can create an ultra thin film membrane of GaN that resembles a "nano-roof" to which the dislocations are attached.
Nanoball
Researchers say that each dislocation has a "root" shaped like a nanoball that has pronounced features such as clustering along definite lines and loops forming mosaic structures.
Emission
The researchers also found that the dislocation networks emit mainly yellow light, while the GaN nano-roof emits both UV and yellow. The prevailing yellow part is probably related to point defects trapping the negative charge that shields the material against PEC etching.
Applications of GaN membranes
Making nanometre-thin GaN membranes transparent to both electrons and UV-light have good electrical conductivity. This fabricating technique of thin gallium nitride membranes could help better to explore two-dimensional GaN-based structures predicted to be ferromagnetic with defect-induced half-metallic configurations, particularly important for spintronics applications.