Abstract
The realization of high-speed and high-power gallium nitride (GaN)-based devices using high-quality GaN/Aluminum nitride (AlN) materials has become a hot topic. Raman spectroscopy has proven to be very useful in analyzing the characteristics of wide band gap materials, which reveals the information interaction of sample and phonon dynamics. Four GaN samples grown on different types of buffer layers were fabricated and the influence of graphene and sputtered AlN on GaN epitaxial layers were analyzed through the E2 (high) and A1 (LO) phonon. The relationship between the frequency shift of E2 (high) phonons and the biaxial stress indicated that the GaN grown on the graphene/sputtered AlN buffer layer was stress-free. Furthermore, the phonon lifetimes of A1 (LO) mode in GaN grown on graphene/sputtered AlN buffer layer suggested that carrier migration of GaN received minimal interference. Finally, the Raman spectra of graphene with the sputtered AlN interlayer has more disorder and the monolayer graphene was also more conducive to nucleation of GaN films. These results will have significant impact on the heteroepitaxy of high-quality thin GaN films embedded with a graphene/sputtered AlN buffer, and will facilitate the preparation of high-speed GaN-based optoelectronic devices.
Highlights
As a group-III nitrides semiconductor, gallium nitride (GaN) materials with superior properties such as wide electronic energy band, wurtzite structural symmetry, strong atomic bonds, high thermal conductivity and so on, have shown major potential in the manufacturing field of optoelectronic devices [1,2]
Through analyzing the E2 and A1 (LO) phonons in GaN epitaxial layer grown by metal-organic chemical vapor deposition (MOCVD) with four different types of buffer layers, the peak shift of the E2 phonon peak was found to be the lightest shift, which suggested that the stress that the GaN films grown on the graphene/sputtered aluminum nitride (AlN) buffer layer suffered was lowest
Through Raman analysis of GaN and graphene, it is concluded that the GaN obtained on the graphene/sputtered AlN buffer layer was subject to stress-free conditions, and the single-layer graphene obtained by the wet-transfer was more conducive to nucleation in the growing process
Summary
As a group-III nitrides semiconductor, gallium nitride (GaN) materials with superior properties such as wide electronic energy band, wurtzite structural symmetry, strong atomic bonds, high thermal conductivity and so on, have shown major potential in the manufacturing field of optoelectronic devices [1,2]. GaN has demonstrated broad development prospects in the application of high-brightness blue/green light emitting diodes (LEDs), blue laser diodes (LDs), photoelectric detectors and deep ultraviolet optoelectronic devices [3–5]. It is known that the the stress in the GaN epilayer caused by the lattice constants and thermal expansion coefficient mismatch between the substrate and GaN films is still an extremely critical issue in the current study [6–8]. The existence of stress will induce defects, which are considered as the primary factor restraining further development of high efficiency III-nitride.
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