Microscopic study of the surfactant‐assisted Si, Ge epitaxial growth
The Sb‐assisted Si, Ge epitaxial growth processes have been studied using high resolution photoemission. It is found that the initially ordered Sb monolayer on the Si(100) and Ge(100) surfaces occupies the epitaxial sites and fully saturates the surface dangling bonds. This results in a reduction of the surface energy. During the growth process, the Sb atoms and the deposited Si, Ge atoms change their positions. Sb atoms segregate to the growth front to form a new ordered layer while leaving the uniform epitaxial Si, Ge layer behind.
Large electropositive cations as surfactants for the growth of polar epitaxial films
Since the discovery of the high mobility quasi-2dimensional electron gas (q-2DEG) at the n-type interface between LaAlO3 (LAO) and SrTiO3 (STO) [1], enormous experimental and theoretical efforts have been made to understand its origins and its relation to the polar, crystallographic orientation induced electric potential which diverges with film thickness [2–4]. Although the issue is still under debate, there is now a general consensus that compensation of this diverging electric potential (the polar catastrophe) is achieved through a combination of pure electronic reconstruction [3–5], interface defects [6, 7], lattice distortions [8, 9], and oxygen vacancies [7, 10–23]. The last mechanism is particularly noteworthy as recent studies [7, 23] argue that the formation of oxygen vacancies on the AlO2 surface provides a comprehensive explanation for the observed critical thickness of four LAO layers required for the q-2DEG to appear. The relative contributions of these mechanisms to removing the polar catastrophe is expected to depend critically on the specific details of the growth conditions. This explains why samples grown by different groups can show widely dissimilar properties [24]. The important role played by defects and vacancies [3] also explains why the growth of clean LAO/STO interfaces, necessary for device applications, has proven to be such a challenge. In this Letter we propose a solution for this challenge. We use DFT calculations to show that a coverage of 1/2 K per unit cell of the AlO2 surface acts like a surfactant that stabilizes the epitaxial growth of the polar LAO. Each K donates an electron to the LAO/STO interface, generating a q-2DEG while keeping the top surface of LAO insulating. This q-2DEG fully compensates for the polar catastrophe for any thickness of the LAO film, removing the reason for the appearance of defects, vacancies or distortions. Moreover, because of their large size, the K ions cannot enter substitutionally into LAO film. As a result, after the deposition of half a monolayer of K, the epitaxial LAO film will grow cleanly under this surfactant.
Photoreflectance characterization of vanadium-doped GaAs layers grown by metalorganic vapor phase epitaxy
Abstract We characterized the vanadium-doped (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy. The conductivity of the samples is checked by the Hall effect measurements, and it is n type with electrons concentration ranging from 2×10 13 to 2×10 17  cm −3 . We used the photoreflectance technique (PR) to study the effect of vanadium doping on the optical properties of GaAs. Our experimental results show that the built-in electric field F and the broadening parameter Γ 0 increase with V-doping concentration. Furthermore, the temperature dependence of the built-in electric field and the broadening parameter of GaAs:V samples have been investigated by PR. It has been observed that these parameters increase with increasing temperature. The decrease of the built-in electric field with decreasing temperature is due to the photovoltage effect.We characterized the vanadium-doped GaAs (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy.