Kinetic stabilization of a pristine Fe film on(4×2)−GaAs(100)

Abstract

We grow Fe film on (4 × 2)-GaAs(100) at low temperature, (∼ 130 K) and study their chemical structure by photoelectron spectroscopy using synchrotron radiation. We observe the effective suppression of As segregation and remarkable reduction of alloy formation near the interface between Fe and substrate. Hence, this should be a way to grow virtually pristine Fe film on GaAs(100).Further, the Fe film is found stable against As segregation even after warmed up to room temperature. There only forms very thin, ∼ 8Å thick interface alloy. It is speculated that the interface alloy forms via surface diffusion mediated by interface defects formed during the low temperature growth of the Fe film. Further out-diffusion of both Ga and As are suppressed because it should then proceed via inefficient bulk diffusion.1 Fe film on GaAs(100) has been extensively studied as a representative system for ferromagnetic metal-semiconductor heterostructure.[1] Due to the small lattice mismatch (∼ 1.3%) between the double of the lattice constant of Fe and that of GaAs, epitaxial growth of Fe film on GaAs(100) is achieved. However, alloy formation near the interface and serious outdiffusion of both Ga and As from the bulk have been notorious problems.[2, 3, 4] There have been various attempts to solve those problems such as S-passivation of GaAs surface[5] and insertion of Er layer between Fe and GaAs [6]. For both cases, the interfacial reaction is reduced to some extent, but the segregated As is still observed. Chye et al. [7] grow Fe film on GaAs (100) at 120 K and also insert Al interlayer. They find improved squareness in magnetic hysteresis and reduced interface states in photo-luminescence spectra. However, no direct investigation on atomic and chemical structure of the Fe film is made.In the present work, we grow Fe film on GaAs(100) around 130 K, and examine the possibility of kinetic stabilization of the Fe film by photoelectron spectroscopy. Here, we report direct evidence for the effective suppression of the outdiffusion of both Ga and As and the minimal formation of the interface alloy during the growth of the Fe film. When the film is warmed up to room temperature, there forms very thin alloy limited near to the interface. Further outdiffusion of both Ga and As is, however, still suppressed.All the experiments are performed at 2B1 beam line of Pohang light source in Korea. It is equipped with an electron energy analyzer and low energy electron diffraction (LEED) optics. The base pressure of the chamber is below 5 × 10 −10 Torr. For the substrate, we use Si-doped, n-type GaAs(100). Repeated sputtering and annealing produce clean and wellordered GaAs substrate; sputtering is made by Ar ion beam of 0.5 K eV, with its incidence angle 45 o from surface normal to minimize surface damage. Annealing is made at 840 K for 30 minutes. As-prepared surface shows well-defined 4 × 2 LEED pattern.We use an e-beam evaporator to deposit Fe film whose thickness is determined by a quartz microbalance that is calibrated by in situ surfac...

Structural investigation of the three-layer system MgO/Fe/GaAs(001) by means of photoelectron spectroscopy and diffraction

“…22,23 As a result, the previously proposed structure (from STM images) of the GaAs (4 × 2) reconstruction 24,25 is impressively confirmed by XPD. Up until now it was unclear whether the Fe film undergoes a structural change if MgO is prepared on top of Fe.…”

Kinetic stabilization of Fe film on GaAs(100): An in situ X-ray reflectivity study

“…This suggests that no significant chemical reactions of the Fe and the Ga(As) have occured. This result is consistent with the observation of the recent photoelectron spectroscopy that finds effective suppression of the outdiffusion of both Ga and As, and negligible interface alloying in an Fe film grown on GaAs(1 0 0) at 130 K [11].…”

“…This might be attributed to the small amount of Ga or As atoms that have out-diffused through the interface. Actually, recent photoelectron spectroscopy of the Fe film grown on GaAs(1 0 0) at 130 K observes the appearance of As peak, although very small, when the film is annealed above room temperature, and attributes it to the outdiffused As atoms far below the surface [11]. We conclude that the pristine Fe film is mostly conserved or kinetically stabilized at room temperature, although small amount of As atoms might have diffused through the interface.…”

“…However, structural and chemical analysis confirming the assumed growth behavior of Fe/ GaAs(1 0 0) at the low temperature has not been done. Only recently, photoelectron spectroscopy has been performed on Fe films grown on GaAs(1 0 0) at 130 K, and suggested that the alloy formation and outdiffusion of both Ga and As be effectively suppressed [11]. The atomic structure of the interface has also been studied by Z-contrast electron microscopy [12].…”

Interface Magnetism in Ferromagnetic Metal–compound Semiconductor Hybrid Structures

“…In MBE growth it was, until fairly recently, common for ferromagnetic contacts to semiconductors to be grown at slightly elevated temperatures, usually in the range 50-300 • C. However, lowtemperature MBE growth of Fe on GaAs(001) has more recently been used in an attempt to enhance the interface cleanliness by Lee et al 88 . They found that by reducing the GaAs substrate temperature to around 130 K they could suppress both outdiffusion of As and Ga from the substrate, and interfacial intermixing, during Fe film growth.…”