Abstract
Through nanoscratch experiments with a spherical diamond indenter, a contrastive study of the nanotribological properties of Ga- and N-faced gallium nitride (GaN) samples was carried out. Nanoindentation results revealed that the elastic modulus of the Ga-faced GaN sample was slightly higher than that of N-faced GaN sample. Particularly, Ga- and N-faced GaN samples exhibited rather different nanotribological properties, and the Ga-faced sample showed a stronger wear resistance. The study indicated that the critical normal load required to cause material removal of N-faced GaN sample was almost two times that of Ga-faced GaN sample. Both Ga- and N-faces exhibited a rather low frictional coefficient at the elastic and elastoplastic stages of material, e.g., ~0.06 for Ga-face and ~0.075 for N-face when scratching under the progressive normal load. Combined with transmission electron microscopy and X-ray photoelectron spectroscopy, we speculated that, except for the intrinsic atomic arrangements attributed to the non-reverse crystallographic symmetry of c-plane wurtzite GaN, the difference of nanotribological properties between Ga- and N-faces may also be related to the preferential formation of a native oxide layer and a slight lattice damage layer on the N-faced GaN surface. This study can enrich the understanding of the nanotribological properties of Ga- and N-polar-faced bulk monocrystalline GaN materials fabricated by the conventional technique.
Highlights
By virtue of its wide forbidden band, direct energy gap, high temperature, and pressure resistance, etc., gallium nitride (GaN) has been widely used in blue/green/ultraviolet light emitting diodes (LEDs) [1,2], high electron mobility transistors [3,4], high power and frequency electronic devices [5,6], and so on
We found that when the normal load was further increased to ~4200 μN, obvious material removal eventually occurred on the Ga-face GaN surface and the groove depth sharply increased to ~40 nm
With the increase of normal load, the nanoscratch-induced deformation of GaN went through the three stages of pure elastic, elastoplastic, and material removal, on both the Ga-faced and N-faced GaN surfaces
Summary
By virtue of its wide forbidden band, direct energy gap, high temperature, and pressure resistance, etc., gallium nitride (GaN) has been widely used in blue/green/ultraviolet light emitting diodes (LEDs) [1,2], high electron mobility transistors [3,4], high power and frequency electronic devices [5,6], and so on. During the processes of preparation, packaging, and transportation of GaN-based devices, e.g., LEDs, a dislocation or defect can be produced under the slight stress and creep effect (usually caused by the normal load and frictional force at micro/nanoscale) [7,8], which would lead to the reduction of photoelectric conversion efficiency of LEDs [9]. Even avoid, the negative influences of friction and wear on the luminous performance of LEDs, the understanding of the nanotribological properties of GaN material is quite essential. Therein, the nanotribological properties (e.g., wear at nanoscale) of GaN material is a key factor influencing the material removal efficiency and lattice damage behavior. The study of nanotribological properties could help to understand the atomic-level CMP mechanism [11,12]
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