Initial stages of MnAs/GaAs(0 0 1) epitaxy studied by RHEED azimuthal scans

We study the nucleation phase of molecular beam epitaxy of (hexagonal) MnAs on (cubic) GaAs (0 0 1) using reflection high-energy electron diffraction (RHEED) azimuthal scans. The nucleation proceeds from a non-reconstructed initial stage through randomly oriented small nuclei and two orientation stages to the final single-phase epitaxial orientation. The fascinatingly complex nucleation process contains elements of both Volmer-Weber and Stranski-Krastanov growth. The measurement demonstrates the potential of high-resolution RHEED techniques to assess details of the surface structure during epitaxy.     

SiC衬底上异质外延GaN薄膜结构缺陷对黄光辐射的影响

利用光致发光技术对在SiC衬底上采用MOCVD异质外延未故意掺杂的GaN进行发光特性的研究,发现在室温下有很强的黄光输出,同时,采用扫描电子显微术和X光衍射对样品的表面形貌和结构进行了研究,结果发现,随着缺陷密度的减少,黄光输出强度也有所降低,因此,黄光输出强度与缺陷有很大的关系.     

Analysis of an Energy Localization Approximation applied to three-dimensional Kinetic Monte Carlo simulations of heteroepitaxial growth

Heteroepitaxial growth involves depositing one material onto another with a different lattice spacing. This misfit leads to long-range elastic stresses that affect the behavior of the film. Previously, an Energy Localization Approximation was applied to Kinetic Monte Carlo simulations of two-dimensional growth in which the elastic field is updated using a sequence of nested domains. We extend the analysis of this earlier work to a three-dimensional setting and show that while it scales with the increase in dimensionality, a more intuitive Energy Truncation Approximation does not.     

GaAs/InP异质外延材料的光致发光研究

首次对MOCVD-LPE混合外延生长的GaAs/InP材料进行了光致发光测量及分析。结果显示出混合生长的GaAs发光强度明显高于MOCVD一次外延生长的GaAs的发光强度,并确认在16K温度下GaAs和InP有跃迁激子产生。观测到GaAs/InP样品近带边光致发光谱的半峰宽为8.4meV,显示了这种材料的高质量。     

Metalorganic vapor phase epitaxy of III–V-on-silicon: Experiment and theory

The integration of III–V semiconductors with Si has been pursued for more than 25 years since it is strongly desired in various high-efficiency applications ranging from microelectronics to energy conversion. In the last decade, there have been tremendous advances in Si preparation in hydrogen-based metalorganic vapor phase epitaxy (MOVPE) environment, III–V nucleation and subsequent heteroepitaxial layer growth. Simultaneously, MOVPE itself took off in its triumphal course in solid state lighting production demonstrating its power as industrially relevant growth technique. Here, we review the recent progress in MOVPE growth of III–V-on-silicon heterostructures, preparation of the involved interfaces and fabrication of devices structures. We focus on a broad range of in situ, in system and ex situ characterization techniques. We highlight important contributions of density functional theory and kinetic growth simulations to a deeper understanding of growth phenomena and support of the experimental analysis. Besides new device concepts for planar heterostructures and the specific challenges of (001) interfaces, we also cover nano-dimensioned III–V structures, which are preferentially prepared on (111) surfaces and which emerged as veritable candidates for future optoelectronic devices.     

SiC衬底上异质外延GaN薄膜XPS谱和PL谱研究

利用X射线光电子能谱,对在SiC衬底上采用MOCVD异质外延的未故意掺杂的GaN进行N、Ga组份测试,同时用光致发光技术对样品进行发光特性的研究.结果表明,随着GaN薄膜中Ga百分含量逐渐减小,室温下黄光输出峰值强度却逐渐增加.因此,在Ga含量相对低的GaN薄膜中容易形成Ga空位(即Ga空位浓度较高),而此时,黄光辐射强度单调递增证明,黄光辐射与VGa密切相关.     

One-dimensional Ge nanostructures on Si(001) and Si(1 1 10): Dominant role of surface energy

Ge/Si(001) is a prototypical system for investigating three-dimensional island self-assembly owed to the Stranski–Krastanow growth mode. More than twenty years of research have produced an impressive amount of results, together with various theoretical interpretations. It is commonly believed that lattice-mismatch strain relief is the major driving force leading to the formation of these islands. However, a set of recent results on Si(001) and vicinals point out that, under suitable conditions, this is not the case. Indeed, we here review experimental and theoretical results dealing with nanostructures mainly determined by surface-energy minimization. Results are intriguing, as they reveal the existence of magic sizes, show the presence of very peculiar morphologies, such as micron-long wires, and distinguish among attempts to facet the wetting-layer and true SK islands.     

Effects of substrate shape, curvature and roughness on thin heteroepitaxial films of Pt on Au(1 1 1)

The growth of thin (1–10 nm) films of Pt on Au(1 1 1) was studied in order to understand and clarify differences in growth mode observed in ultra-high vacuum (UHV) studies and in electrochemical deposition studies. It was found that on flat Au(1 1 1), Pt grows in a layer-by-layer growth mode, but if the gold substrate is exposed to an acidic environment prior to Pt deposition, then the substrate becomes nanoscopically rough (islanded) and Pt growth follows a pseudo-Stranski–Krastanov (SK) growth mode in which an initially thin wetting layer becomes rougher with increasing film thickness. An analysis of curvature effects on epitaxial growth mode shows that thermodynamic curvature effects involving surface stress are negligible for the Pt/Au(1 1 1) system. Rather, the apparent SK growth is linked to kinetic effects associated with inhomogeneous in-plane elastic relaxation of Pt films on rough surfaces that drive Pt atoms from pits to the tops of islands in the early stages of growth. Implications for the control of epitaxial film roughness are discussed.     

“Temperature oscillation” as a real-time monitoring of the growth of 3C-SiC on Si substrate

Pyrometric interferometry has been observed during gas-source molecular beam epitaxy (GSMBE) of 3C-SiC on Si substrate using monomethyl silane. The period of the “temperature oscillation” is shown to correspond to λ/2n, with the λ and n being the wavelength used in the monochromatic optical pyrometry and the refractive index of the grown film, respectively. As is the case for other heteroepitaxies, pyrometric interferometry may provide a feasible real-time monitoring method for the growth of 3C-SiC film on Si substrates.     

Evolution of morphology and composition in three-dimensional fully faceted strained alloy crystals

Alloy structures such as core-shell particles, heteroepitaxial multilayers and nanowires have received a lot of attention in recent years due to their applications in logic, energy storage and optoelectronics. In typical growth conditions, the surfaces of these structures are usually faceted i.e. they adopt low-energy singular crystalline orientations. For alloy systems, the growth law for a fully faceted structure requires the specification of the normal velocity of each facet, the incorporation rate of each alloy component on the surface, and the exchange of surface atoms with the bulk. The latter process requires consideration of both surface segregation and possibly bulk material transport. By using only fundamental concepts of thermodynamics, we derive the governing equations for the growth of strained and fully faceted two-component crystals in regimes where surface material transport may be governed by surface-attachment limited kinetics or surface diffusion limited kinetics. In both cases we derive a very compact form for the surface mass fluxes from chemical potentials that account for the constraint stemming from the fact that while the growth rate of each alloy component can vary along the surface (as governed by the individual chemical potentials), their sum should remain constant along the facet and should be equal to the growth velocity of the facet. Within our approach, the dynamics of surface segregation and other important features of faceted crystal growth that lead to compositional patterning such as a kinetic barrier for exchange of alloy components between different facets emerge in a very natural fashion.