Reduction of Residual Impurities in Homoepitaxial m‐Plane GaN by Using N₂ Carrier Gas in Metalorganic Vapor Phase Epitaxy

Abstract

The reduction of unintentional impurities in m-plane 10 10Þð GaN homoepitaxial layers is demonstrated by using nitrogen (N 2 ), as opposed to hydrogen (H 2 ), as carrier gas in metalorganic vapor phase epitaxy (MOVPE). Secondary ion mass spectrometry (SIMS) analysis shows that the impurity levels of residual oxygen (O), carbon (C), and silicon (Si) are decreased by nearly one order of magnitude in N 2 -grown samples. Although the full width at half maximum (FWHM) values for the on-axis m-plane X-ray rocking curves of all specimens are quite similar (around 50 arcsec), plan-view scanning transmission electron microscopy (STEM) measurements reveal a clear reduction of dislocation densities in N 2 -grown films. Their origin is likely related to an initial surface roughening with H 2 carrier gas, which also causes surface faceting resulting in the formation of large four-sided pyramidal hillocks, while using N 2 results in smoother surfaces. Hence, MOVPE growth with N 2 carrier gas is an effective method to lower the impurity incorporation in mplane GaN materials in addition to reducing the formation of defects and improving the surface morphology, which can enable the development of high-performance GaN-based devices on non-polar surfaces.GaN is an attractive material for optoelectronics and high-power electronics applications, due to its direct wide band gap, high electron mobility, high electron saturation velocity, high stability and conductivity. GaN materials grown in non-polar orientations (a-or m-plane) are devoid of spontaneous polarization and piezoelectric fields which can enable novel highperformance electronic devices owing to the suppression of the quantum confined Stark effect. [1] As a result, extensive and ongoing research efforts have been devoted to the growth and characterization of nonpolar nitrides worldwide in order to better comprehend their material properties and challenges. Moreover, the advent of low defect lattice-matched bulk GaN substrates has provided a significant progress for high-quality GaN crystals, and improved performance of GaN-based devices. [2] Hitherto, promising results have been reported for light-emitting diodes, [3] laser diodes, [4] and normally off high-electron-mobility transistors [5] on nearly dislocation-free m-plane GaN (m-GaN) substrates. However, homoepitaxial m-GaN films grown on nominally on-axis bulk GaN by metalorganic vapor phase epitaxy (MOVPE) commonly exhibit wavy surface morphologies featuring pyramidal hillocks and are prone to high impurity intake. [6][7][8] While the surface morphology can be improved by using much expensive miscut GaN substrates, [6] the higher unintentional oxygen (O), carbon (C), and silicon (Si) impurities incorporation in m-plane GaN layers remains an issue which hinders further progress in device performance and reliability. Therefore, it is crucial to enhance the material properties of homoepitaxial m-plane GaN in the most cost-effective way via epitaxial growth engineering.Early works on the MOVPE growth of III-V materials es...

Core–shell GaN/AlGaN nanowires grown by selective area epitaxy

“…Barry et al have recently reported the presence of a heavily undulated surface in the planar homoepitaxial growth of m -plane GaN using a H 2 carrier gas, whereas, growth in a N 2 carrier gas promoted the formation of atomically flat surface resulting in m -plane GaN with reduced oxygen, carbon, and silicon impurities. 33 Earlier work on using pure N 2 as a carrier gas have also demonstrated significantly improved homogeneity, layer purity, and crystal quality in Al-containing ternary AlGaAs alloys, 34 and superior optical properties in a planar AlN epitaxial layer. 35 Similar to our growth of GaN nanowires in the presence of H 2 followed by AlGaN grown in a pure N 2 carrier gas, Yamaguchi et al reported a planar GaN grown in a H 2 carrier gas followed by a GaN/Al 0.17 Ga 0.83 N MQW grown in a N 2 carrier gas which had had superior crystalline and optical properties.…”