Fangliang Gao

Epitaxial growth of high quality AlN films on metallic aluminum substrates

AlN (0001) epitaxial films have been grown on Al (111) substrates with an in-plane epitaxial relationship of AlN[110]//Al[10] by pulsed laser deposition. The as-grown AlN films grown at 450 °C exhibited a very smooth and flat surface with a surface root-mean-square roughness less than 1.1 nm. There is no interfacial layer existing between AlN films and Al substrates, indicating an abrupt interface. The as-grown ~302 nm thick AlN films are almost fully relaxed only with an in-plane compressive strain of 0.16%. With the increase in growth temperature, the interfacial layer thickness increases, resulting in the degradation in the crystalline quality of the as-grown AlN films. These AlN films are of great interest for the commercial development of AlN-based devices.

Deposition of nonpolar m-plane InGaN/GaN multiple quantum wells on LiGaO2(100) substrates

High-quality nonpolar m-plane InGaN/GaN multiple quantum wells (MQWs) have been deposited on LiGaO2(100) substrates by the combination of pulsed laser deposition (PLD) and molecular beam epitaxy (MBE) technologies. This work opens up a new prospect for achieving high-efficiency nonpolar m-plane GaN-based devices.

Plasmon-enhanced ultraviolet photoluminescence from highly ordered ZnO nanorods/graphene hybrid structure decorated with Au nanospheres

Highly ordered and vertically aligned ZnO nanorods using an inverted self-assembled monolayer (SAM) template was fabricated via the hydrothermal process, and few-layer graphene was transferred on the surface of the ZnO nanorod arrays with 20 nm Au nanospheres coverage on the graphene surface. The band edge emission of the ZnO nanorods/graphene hybrid structures with Au nanospheres was increased by approximately three times and the defect-related emission was significantly reduced compared with the pristine ZnO nanorods arrays. The improved PL intensity can be attributed to the resonant coupling between the exciton emission of ZnO nanorods and plasmonic effects of graphene-Au structures. Our results will be promising for designing and fabricating ordered ZnO nanorod-based optical and optoelectronic devices.

Effect of Al evaporation temperature on the properties of Al films grown on sapphire substrates by molecular beam epitaxy

High-quality Al films with an in-plane epitaxial relationship of Al[1−10]//sapphire[1−100] have been epitaxially grown on sapphire substrates by molecular beam epitaxy. The as-grown and ∼200 nm thick Al films prepared at an Al evaporation temperature of 1100 °C were highly crystalline, with a full-width at half-maximum of 180 arcseconds, and had a very smooth surface, with a root mean square roughness of 0.6 nm. There was no interfacial layer between the Al and sapphire. Furthermore, the effect of the Al evaporation temperature on the properties of the as-grown ∼200 nm thick Al films has been studied in detail. This work of achieving high-quality Al films is of great importance for the fabrication of high-performance Al-based devices.

Effect of InGaAs interlayer on the properties of GaAs grown on Si (111) substrate by molecular beam epitaxy

High-quality GaAs films have been epitaxially grown on Si (111) substrates by inserting an InxGa1−xAs interlayer with proper In composition by molecular beam epitaxy (MBE). The effect of InxGa1−xAs (0 < x < 0.2) interlayers on the properties of GaAs films grown on Si (111) substrates by MBE has been studied in detailed. Due to the high compressive strain between InGaAs and Si, InGaAs undergoes partial strain relaxation. Unstrained InGaAs has a larger lattice constant than GaAs. Therefore, a thin InGaAs layer with proper In composition may adopt a close lattice constant with that of GaAs, which is beneficial to the growth of high-quality GaAs epilayer on top. It is found that the proper In composition in InxGa1−xAs interlayer of 10% is beneficial to obtaining high-quality GaAs films, which, on the one hand, greatly compensates the misfit stress between GaAs film and Si substrate, and on the other hand, suppresses the formation of multiple twin during the heteroepitaxial growth of GaAs film. However, when t...

Achieving high-quality In0.3Ga0.7As films on GaAs substrates by low-temperature molecular beam epitaxy

The effects of the thickness of the large-mismatched amorphous In0.6Ga0.4As buffer layer on In0.3Ga0.7As epi-films grown on a GaAs substrate have been systematically investigated. The In0.3Ga0.7As films with the In0.6Ga0.4As buffer layer of 0, 1, 2, and 4 nm thickness are grown by low-temperature molecular beam epitaxy (LT-MBE) and are characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It is found that the degree of relaxation and the crystallinity of the as-grown In0.3Ga0.7As films are strongly affected by the thickness of the amorphous In0.6Ga0.4As buffer layer. The thinner In0.6Ga0.4As buffer layer is not enough to efficiently release the misfit strain between the In0.3Ga0.7As epilayer and the GaAs substrate, while the thicker In0.6Ga0.4As buffer layer is unfavorable to trap the dislocations and prevent them from extending into the In0.3Ga0.7As epi-films. We have demonstrated that the amorphous In0.6Ga0.4As buffer layer with a thickness of 2 nm can advantageously prevent threading and misfit dislocations from propagating into the subsequent In0.3Ga0.7As epilayer and increase the degree of relaxation of the as-grown In0.3Ga0.7As, ultimately leading to a high-quality In0.3Ga0.7As film. Our novel buffer layer technology has triggered a simple but effective approach to grow high-crystallinity In0.3Ga0.7As epitaxial film and is favorable for fabrication of GaAs-based high-efficiency four-junction solar cells.

Strain relaxation of the In0.53Ga0.47As epi-layer grown on a Si substrate using molecular beam epitaxy

In0.53Ga0.47As films were grown on a Si (111) substrate with two different InxGa1−xAs buffer layers using molecular beam epitaxy (MBE). The effect of buffer layer on the as-grown In0.53Ga0.47As epi-layers was investigated using X-ray diffraction (XRD), reciprocal space mapping (RSM), Raman and transmission electron microscopy (TEM). XRD results showed that the crystalline quality of the as-grown In0.53Ga0.47As epi-layer grown on the Si substrate, using a low-temperature In0.4Ga0.6As buffer layer with in situ annealing, was better than that grown using In0.2Ga0.8As/In0.4Ga0.6As buffer layers. Moreover, the misfit strain between the In0.53Ga0.47As epi-layers and the Si substrate was nearly completely released by inserting a single In0.4Ga0.6As buffer layer grown at 390 °C with in situ annealing at 560 °C. Specifically, the relaxation value of the In0.53Ga0.47As epi-layer with the single In0.4Ga0.6As buffer layer was 97.16%. The lattice mismatch strain of the In0.53Ga0.47As epi-layer was well confined to the In0.4Ga0.6As buffer layer, without being extended to the subsequently grown In0.53Ga0.47As epi-layer compared with its counterpart using the In0.2Ga0.8As/In0.4Ga0.6As buffer layers. The low-temperature In0.4Ga0.6As buffer layer shows a way to realize fully relaxed In0.53Ga0.47As films with a high crystalline quality on the Si substrate.

The temperature dependence of atomic incorporation characteristics in growing GaInNAs films

We have systematically studied the temperature dependence of incorporation characteristics of nitrogen (N) and indium (In) in growing GaInNAs films. With the implementation of Monte-Carlo simulation, the low N adsorption energy (−0.10 eV) is demonstrated. To understand the atomic incorporation mechanism, temperature dependence of interactions between Group-III and V elements are subsequently discussed. We find that the In incorporation behaviors rather than that of N are more sensitive to the Tg, which can be experimentally verified by exploring the compositional modulation and structural changes of the GaInNAs films by means of high-resolution X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, and secondary ion mass spectroscopy.

Growth of InAs Quantum Dots on GaAs (511)A Substrates: The Competition between Thermal Dynamics and Kinetics.

The growth process of InAs quantum dots grown on GaAs (511)A substrates has been studied by atomic force microscopy. According to the atomic force microscopy studies for quantum dots grown with varying InAs coverage, a noncoherent nucleation of quantum dots is observed. Moreover, due to the long migration length of In atoms, the Ostwald ripening process is aggravated, resulting in the bad uniformity of InAs quantum dots on GaAs (511)A. In order to improve the uniformity of nucleation, the growth rate is increased. By studying the effects of increased growth rates on the growth of InAs quantum dots, it is found that the uniformity of InAs quantum dots is greatly improved as the growth rates increase to 0.14 ML s(-1) . However, as the growth rates increase further, the uniformity of InAs quantum dots becomes dual-mode, which can be attributed to the competition between Ostwald ripening and strain relaxation processes. The results in this work provide insights regarding the competition between thermal dynamical barriers and the growth kinetics in the growth of InAs quantum dots, and give guidance to improve the size uniformity of InAs quantum dots on (N11)A substrates.

Quantum Dots: Growth of InAs Quantum Dots on GaAs (511)A Substrates: The Competition between Thermal Dynamics and Kinetics (Small 31/2016).

On page 4277, G. Li and co-workers aim to promote III-V compound semiconductors and devices for a broad range of applications with various technologies. The growth process of InAs quantum dots on GaAs (511)A substrates is systematically studied. By carefully controlling the competition between growth thermal-dynamics and kinetics, InAs quantum dots with high size uniformity are prepared, which are highly desirable for the fabrication of high-efficiency solar cells.