(Invited) Properties of Cubic GaN Films Deposited on c-BN/Diamond Templates
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2025-07-11 |
| Journal | ECS Meeting Abstracts |
| Authors | Jaime A. Freitas, James C. Culbertson |
Abstract
Section titled āAbstractāCubic GaN (c-GaN) has attracted increasing interest because has several intrinsic advantages over its wurtzite-GaN polymorph. Namely, no polarization in the <100> growth direction, smaller bandgap, lighter electron and heavy hole effective masses, larger optical gain, shorter radiative recombination lifetime, smaller p-doping activation energy (Mg acceptor), higher hole mobility, and larger conduction band offset. Consequently, c-GaN could enable the next-generation of high efficiency visible light-emitting diodes, normally-off AlGaN/GaN high speed power transistors, and resonant tunnel diodes. However, the synthesis of c-GaN has been a great challenge due to its metastability. To date, c- GaN films have been deposited on cubic substrates such as GaAs, c-SiC, Si, and more recently on patterned Si(100) wafers [1-5]. This work demonstrates that c-GaN can be deposited on diamond substrates, which could considerably improve thermal management, enabling its potential application for high-speed and high-power devices. c-GaN epitaxial film was grown directly on a boron nitride nucleation layer, previously deposited on <100> type IIA CVD-diamond, by plasma-assisted molecular-beam epitaxy with no additional surface preparation and under conditions (e.g. substrate temperature, nitrogen and gallium fluxes) that result in wurtzite-GaN when grown on hexagonal substrates [6]. The thickness of the GaN top layer is estimated to be ~120 nm. XRD measurements verified that <100> zincblende is the dominant crystalline phase, with a small contribution from the wurtzite phase at some sample regions. However, no wurtzite-GaN inclusion were observed in the film region dominated by crystal with cubic symmetry, as highlighted in the AFM imaging. Polarized Raman scattering measurements of these regions confirmed the XRD findings. Low temperature (6K) photoluminescence spectra show a dominant line near 3.12 eV and a weaker line near 3.21 eV. The former is assigned to a recombination process involving electrons bound to shallow donors with holes bound to shallow acceptors (DAP recombination). The latter, which becomes dominant at temperatures above 50K, is assigned to recombination processes involving the annihilation of excitons bound to shallow impurities. Room temperature transmission measurements yielded a direct near bandgap of 3.21 eV, which is close to previously reported values. These results verified that c-GaN can be deposited on high thermal conductivity diamond substrates [7]. If the time allows higher lateral resolution measurements will be presented. Our results provide a starting point of a new approach for realizing the potential of c-GaN devices for high-power applications, considering that large area diamond substrates are becoming commercially available. J.N. Kuznia, et al, Appl. Phys. Lett. 65 (1994) 2407 D.J. As, et al., Appl. Phys. Lett. 70 (1997) 1311 J. Wu, et al., Jpn. J. Appl. Phys. 37 (1998) 1440 M. Feneberg, et al., Phys. Rev. B 85 (2012) 155207 R. Liu, et al., ACS Photonics, 5 (2018) 9551 D.F. Storm, et al., Phys. Status Solid RRL 2022 , 220003 J.A. Freitas, et al., accepted for publication in JAP This work supported by the Office of Naval Research