Study of N-polar GaN growth with a high resistivity by metal-organic chemical vapor deposition

• Undoped N-polar GaN with a sheet resistivity of 1.7 × 104 ohm/sq is nearly stress-free.
• The full width at half maximum of N-polar GaN (0002) ω-rocking curve is ∼40 arc sec.
• Resistivity shares the same changing trend with edge dislocation density.

We report the growth of undoped N-polar GaN with a high resistivity on c-plane Al2O3 substrates by metal-organic chemical vapor deposition. The polarity of N-polar GaN has been examined and verified using a wet etching method. It is found that the density of threading dislocations has a great influence on the resistivity of N-polar GaN. By optimizing the V/III ratio, N-polar GaN with a relatively high sheet resistivity of 1.7 × 104 ohm/sq has been obtained. More importantly, the N-polar GaN films in our case are high-crystalline, with a rather low full width at half maximum (FWHM, 30–40 arc sec) of the (0002) ω  -rocking curve. Simultaneously, the sheet resistivities of N-polar GaN films share the same changing trend with the FWHM of (101¯2)ω-rocking curve, reaching a maximum value at a V/III ratio of 1000. Through Raman spectroscopy analysis, the N-polar GaN with a sheet resistivity of 1.7 × 104 Ohm/sq is nearly stress-free. Besides, the optical properties of GaN films have been investigated by photoluminescence measurements to further access the crystallinity of N-polar GaN.