MOVPE grown periodic AlN/BAlN heterostructure with high boron content

In this work we investigate the epitaxial growth of boron containing (Al,Ga)N layers and superlattices for applications in the active region of UV‐LEDs. For AlBN layers containing 5% of boron as quantified by secondary ion mass spectrometry, columnar growth has been observed. Transmission electron microscopy (TEM) studies revealed B‐lean, crystalline columns, separated by highly boron containing amorphous intermediate regions. However, in the first few nanometers of AlBN growth, no evidence of columnar growth can be found. Indeed, first layers of AlBGaN/AlN superlattice stacks do not show any sign of columnar growth. However, for increasing thickness, 3D‐like growth develops through formation of pyramidal structures. TEM‐based selective area electron diffraction analysis does not show evidence of lattice tilting, proving that the observed inclined facets are not a result of lattice twinning. Thin AlBGaN layers with different thickness containing 1% boron show similar photoluminescence (PL) spectra with slightly reduced intensity as compared to similar B‐free AlGaN layers. Although small grainy structures develop and increase in density for AlBGaN layers with a thickness of 10 nm and more, the PL intensity increases steadily with layer thickness, showing that these grains do not drastically deteriorate their luminescence properties.

Section: Resultssupporting

confidence: 90%

Investigation of Boron Containing AlN and AlGaN Layers Grown by MOVPE

Rettig

Scholz

Steiger

et al. 2018

“…Trimethylaluminum (TMA), triethylboron (TEB), and NH 3 were utilized as precursors. In the vapor phase, B/III ratios were kept at 12 and 17% for BAlN‐I and BAlN‐II, respectively, which are considerably lower than that (40%) of the previous reports . With reduced parasitic reaction between metalorganics and NH 3 and efficient incorporation, the boron contents should be higher than 10%.…”

Section: Methodsmentioning

confidence: 79%

“…Phase separation, short diffusion length of boron atoms, and strong parasitic reaction in the gas phase were attributed to the small boron contents. Recently, Li et al reported on the growth of BAlN by a T‐shape horizontal metalorganic chemical vapor deposition (MOCVD) reactor with a much higher boron content of 12% . However, the single‐phase wurtzite structure was only observed in the first 10 nm or thinner region of the BAlN film.…”

Section: Introductionmentioning

confidence: 99%

100‐nm thick single‐phase wurtzite BAlN films with boron contents over 10%

Wang

Liu

et al. 2017

Growing thicker BAlN films while maintaining single‐phase wurtzite structure and boron content over 10% has been challenging. In this study, we report on the growth of 100 nm‐thick single‐phase wurtzite BAlN films with boron contents up to 14.4% by MOCVD. Flow‐modulated epitaxy was employed to increase diffusion length of group‐III atoms and reduce parasitic reactions between the metalorganics and NH3. A large growth efficiency of ∼2000 μm mol−1 was achieved as a result. Small B/III ratios up to 17% in conjunction with high temperatures up to 1010 °C were utilized to prevent formation of the cubic phase and maintain wurtzite structure.

“…Though those studies show the potentials of B x Al 1− x N alloys, many issues have yet to be solved. For example, due to the phase separation, short diffusion length of B, and strong parasitic reaction in the gas phase, the B composition in the B x Al 1− x N alloys remains low . Recently, a high B incorporation of 14.4% in a single‐phase WZ BAlN was achieved with a thin layer of 100 nm .…”

Section: Introductionmentioning

confidence: 99%

Structural and electronic properties of wurtzite B_xAl_1–xN from first‐principles calculations

Zhang

2017

The structural and electronic properties of wurtzite BxAl1−xN (0 ≤ x ≤ 1) are studied using density functional theory. The change of lattice parameters with increased B composition shows small bowing parameters and thus slightly nonlinearity. The bandgap exhibits strong dependence on the B composition, where transition from direct to indirect bandgap occurs at a relatively low B composition (x ∼ 0.12) is observed, above which the bandgap of BxAl1−xN maintained indirect, thus desirable for low‐absorption optical structures. The Γv‐Ac and Γv‐Kc indirect bandgaps are dominant at lower and higher B compositions, respectively. Density of states (DOS) of the valence band is susceptible to the B incorporation. Strong hybridization of Al, B, and N in p‐states leads to high DOS near the valence band maximum. The hybridization of Al and B in s‐states at lower B compositions and p‐states of B at higher B compositions give rise to high DOS near lower end of the upper valence band. Charge density analysis reveals the B‐N chemical bond is more covalent than the Al‐N bond. This will lead to more covalent crystal with increasing B composition. Dramatic change of the heavy hole effective mass is found due to significant curvature increase of the band by minor B incorporation.