Demonstration of single-phase wurtzite BAlN with over 20% boron content by metalorganic chemical vapor deposition

Abstract

Wurtzite BAlN alloys are emerging ultrawide bandgap III-nitride semiconductors promising for optical and electronic devices. Yet the boron compositions of the grown alloys have been limited. In this Letter, we report on the demonstration of a thick single-phase wurtzite BAlN film with a boron composition over 20%. The growth was conducted at 1010 C and 150 Torr with continuous flows of group-III precursors and ammonia with a growth rate of 2.2 lm/h by metalorganic chemical vapor deposition. The boron composition was studied by x-ray diffraction (XRD), secondary neutral mass spectrometry (SNMS), and Rutherford backscattering spectrometry (RBS). The XRD 2h scan exhibited the clear wurtzite BAlN peak 1.82 larger than the AlN peak, indicating the boron composition of 30.9% based on the lattice constants of wurtzite AlN and BN. The SNMS and RBS experiments, independent of strain and defects, revealed that the boron content was 22%. The microstructures of the wurtzite BAlN film were further studied by transmission electron microscopy, showing an initial 5 nm thick layer free of crystal twinning followed by widespread crystal twinning with lattice rotations of 60 clockwise and anticlockwise. The optical transmission experiment manifested that the bandgap of the smaller-lattice BAlN film was 5.1 eV, smaller than that of larger-lattice AlN. This trend was the opposite of the conventional InGaAlN but consistent with theoretical predictions. This study would greatly facilitate the research of material, physics, and devices incorporating the wurtzite BAlN alloys.

Nanoscale compositional analysis of wurtzite BAlN thin film using atom probe tomography

“…15 Recently, single phase wurtzite BAlN with >20% B has been reported. 17 The B content was measured using x-ray diffraction (XRD), secondary neutral mass spectrometry (SNMS), and Rutherford backscattering spectrometry (RBS). While the XRD result suggested a high B content of $30.9%, the B% measured by SNMS and RBS was only $22%.…”

“…While the XRD result suggested a high B content of $30.9%, the B% measured by SNMS and RBS was only $22%. 17 The accuracy of the measured composition is usually compromised in XRD due to the lack of knowledge about the exact BAlN lattice constants at B > 20%. 15 Also, the composition measurement in XRD can be affected by strain and defects in the films.…”

“…10 Also, the BAlN peaks being much weaker than AlN peaks pose a critical challenge in reciprocal space mapping (RSM) in XRD. 15,17 On the other hand, the higher sensitivity of RBS to larger atoms than that for smaller atoms like B could present significant uncertainty in the measured composition. 10 XRD combined with secondary ion mass spectroscopy (SIMS) also provided a significant discrepancy in the B composition, which was attributed to the fact that most of the B formed possible B-related clusters instead of BAlN alloys.…”

“…Impurities such as C, H, and O can be incorporated in BAlN from the trimethylaluminum (TMA), triethylboron (TEB), and ammonia (NH 3 ) precursors and H 2 carrier gas used during growth. 15,17 It is crucial to study the effects of these impurities on the local stoichiometry of the BAlN films. Due to these limitations, the B distribution at the microstructure level remained elusive.…”

“…The details of the growth are recently reported elsewhere. 17 The needle-shaped APT specimens were prepared using an FEI Nova 200 dual-beam focused ion beam (FIB)/scanning electron microscope (SEM) system. The standard lift-out and annular milling techniques were adapted for preparing the sharp APT tips.…”