Mn segregation in Ge/Mn5Ge3 heterostructures: The role of surface carbon adsorption

Abstract

Mn5Ge3 compound, with its room-temperature ferromagnetism and possibility to epitaxially grow on Ge, acts as a potential spin injector into group-IV semiconductors. However, the realization of Ge/Mn5Ge3 multilayers is highly hampered by Mn segregation toward the Ge growing surface. Here, we show that adsorption of some monolayers of carbon on top of the Mn5Ge3 surface prior to Ge deposition allows to greatly reduce Mn segregation. In addition, a fraction of deposited carbon can diffuse down to the underneath Mn5Ge3 layers, resulting in an enhancement of the Curie temperature up to ∼360 K. The obtained results will be discussed in terms of the formation of a diffusion barrier by filling interstitial sites of Mn5Ge3 by carbon.

An unusual phenomenon of surface reaction observed during Ge overgrowth on Mn5Ge3/Ge(111) heterostructures

“…We also note that the Ge deposition rate was precisely measured from RHEED intensity oscillations (error <3%) and at 450 • C. RHEED oscillations of Ge growth on a Ge substrate (Ge homoepitaxy) confirm an almost perfect layer-by-layer growth mode. Contrary to the designed structure and also to TEM images obtained after Ge overgrowth at temperatures below 250 • C (see, for example, figure 1(c) in [24] for Ge overgrowth at 250 • C), the present image reveals that the sample surface is terminated by a Mn 5 Ge 3 layer and no trace of Ge overlayers is detectable. Indeed, the observation in this TEM image of well-defined atomic rows, all being perpendicularly aligned to the interface, can be unambiguously attributed the hexagonal (0001) plane of Mn 5 Ge 3 , which is parallel to the (111) plane of Ge [11].…”

“…Based on the above results it becomes clear that any attempt to produce Ge/Mn 5 Ge 3 /Ge stacked layers should avoid high-temperature Ge deposition to prevent a Ge:Mn reaction forming surface Mn 5 Ge 3 layers. Recently, we have shown that adsorption of some MLs of carbon on the top of Mn 5 Ge 3 followed by Ge deposition at 250 • C, can greatly reduce Mn segregation [24]. The Ge overlayers were shown to be epitaxial with the (111) plane being parallel with the hexagonal (0001) plane of Mn 5 Ge 3 .…”

“…Understanding and controlling the Ge regrowth on Mn 5 Ge 3 constitutes a vital issue for the realization of Ge/Mn 5 Ge 3 /Ge multilayers, which are the basis for numerous applications such as spin valves or the giant magnetoresistance effect. In recent reports, we have shown that for a growth temperature of 250 • C, the Mn segregation is a central problem that needs to be handled in order to get high-quality Mn 5 Ge 3 /Ge stacked layers [23,24]. Here, we report on an unusual phenomenon that occurs during deposition of Ge on the top of a Mn 5 Ge 3 surface at high substrate temperatures, i.e., within the range of 450-550 • C. We show that deposited Ge instantly reacts with Mn to form a Mn 5 Ge 3 surface layer, which continuously floats up the growing surface, leaving behind new Ge layers that serve as a support to maintain the floating Mn 5 Ge 3 layers by epitaxy.…”

Mediation effect of sub‐monolayer carbon on interfacial mixing in Ge growth on Si(100)

“…It is generally accepted that Si and Ge atoms interdiffuse via both vacancy-and interstitial-related mechanisms [5]. It has been reported that filling the vacancy sites near the interface region is effective to prevent the interdiffusion [6][7][8]. Here, carbon (C) atoms with small atomic radius (about half of Ge) is very suitable to fill vacancies, so in this study, mediation effect of C on interfacial mixing in Ge growth were studied using C-covered Si surface (Ge/C/Si) and C over thin Ge buffer layer (Ge/C/Ge/Si) systems.…”

Magnetic critical behavior of Mn5Ge3 ribbons

“…Mn 5 Ge 3 , crystallized in Mn 5 Si 3 ‐type structure, is an interesting multifunctional material, with a great potential application in spintronics 1–4. Its Curie temperature is in the vicinity of room temperature 5, 6, meanwhile, a large entropy change (9.3 J kg −1 K −1 at 50 kOe) near its Curie temperature was reported 7.…”