III-nitride semiconductor films are usually achieved by epitaxial growth on single-crystalline substrates (sapphire, silicon (Si), and silicon carbide). It is important to grow these films on non-epitaxial substrates of interest such as polycrystalline substrates for exploring novel applications in electronics and optoelectronics. However, single-crystalline III-nitride films with uniform orientation on non-epitaxial substrates have not yet been realized, due to the lack of crystallographic orientation of the substrates. Here, this work proposes a strategy of polarization-driven-orientation selective growth (OSG) and demonstrate that single-crystalline gallium nitride (GaN) can in principle be achieved on any substrates. Taking polycrystalline diamond and amorphoussilicon dioxide/Si substrates as typical examples, the OSG is demonstrated by utilizing a composed buffer layer consisting of graphene and polycrystalline physical vapor deposited (PVD) aluminium nitride (AlN). The polarization of the PVD AlN can effectively tune the strength of interfacial orbital coupling between AlN nuclei and graphene at different rotation angles, as confirmed by atom-scale first-principles calculations, and align the AlN nuclei to form a uniform orientation. This consequently leads to continuous single-crystalline GaN films. The ability to grow single-crystalline III-nitrides onto any desired substrates would create unprecedented opportunities for developing novel electronic and optoelectronic devices.
Vertical GaN-on-Si devices are promising for the next-generation high-voltage power electronics with low cost and high efficiency. However, their applications are impeded by the limited thickness of crack-free GaN layers and high threading dislocation density (TDD) in the layer. Buffer layers are crucial for stress control while they usually behave with poor surface morphology, which causes early stress relaxation in GaN and limited thickness. Hereby, a terrace engineering approach for the buffer layers is proposed. Through tuning the supersaturation ratio, the terrace width can be manipulated and an atomically smooth AlGaN buffer layer can be realized, which effectively reduces the compressive stress relaxation and provides a firm foundation for thick GaN growth. As a result, a 7.5 μm thick GaN drift layer with TDD as low as 8.6 × 10 7 cm −2 is achieved on Si substrates. The room temperature electron mobility of the GaN drift layer can be raised up to 1210 cm 2 V −1 s −1 . The fabricated PiN diode shows a high breakdown voltage of 1058 V as well as a high on/off ratio of 10 12 . This work thus truly demonstrates the potential of high-performance and low-cost GaN-based electronic as well as optoelectronic devices on Si platforms.
We present how the interaction between Al dopants and threading dislocations affects dislocation inclinations and then plays an important role in controlling residual strain in GaN-on-Si epitaxial films. When the Al concentration in the GaN epitaxial film is increased to 0.85%, the dislocations extend almost in the growth direction, contributing to a strain-free epitaxial film. We suggest that the Al atoms could substitute for Ga vacancies at the dislocation cores on the growth surface and then inhibit the dislocation inclinations. The suppressed dislocation inclinations lead to a reduced relaxation of compressive strain. The results pave a new way to control dislocation movements and strain in GaN epitaxial films on Si substrates.
In this paper, high-quality β-Ga2O3 films were grown on silicon substrates by plasma-enhanced atomic layer deposition (PEALD). Effects of annealing temperature on β-Ga2O3 thin films were studied. Atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray reflection (XRR), and ultraviolet (UV) emission spectroscopy were used to systematically characterize Ga2O3 thin films. AFM test results showed that as annealing temperature increased from 500 to 900 °C, the roughness of film increased from 0.542 to 1.58 nm. XPS test results showed that the concentration of oxygen vacancies in annealed films was significantly reduced. After annealing, the energy band of the film increased from 4.73 to 5.01 eV, and the valence band maximum (VBM) increased from 2.58 to 2.67 eV, indicating that the annealing treatment under a nitrogen atmosphere can improve the quality of films. Results demonstrate that high-quality Ga2O3 films can be obtained by the annealing process after atomic layer deposition (ALD). The proposed method can realize an ideal stoichiometric ratio of the Ga2O3 thin film as well as precise control of its optical, electrical, and microstructural properties. This work lays the foundation for future application of Ga2O3 materials in photoelectric detection, power devices, transparent electronics, and other fields.
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