Epitaxy of Single Crystal Phase Change Materials on Si(111)
- PDF / 7,347,982 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 85 Downloads / 226 Views
Epitaxy of Single Crystal Phase Change Materials on Si(111) P. Rodenbach1, K. Perumal1, F. Katmis1, W. Braun1,2, R. Calarco1 and H. Riechert1 1 Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany 2 CreaTec Fischer Co. GmbH, Industriestr. 9,74391 Erligheim, Germany ABSTRACT Phase change materials along the GeTe-Sb2Te3 pseudobinary line (GST) are grown by molecular beam epitaxy (MBE) on Si(111). The growth on (111) oriented substrates leads to greatly increased crystal quality compared to (001) oriented substrates, even for a high lattice mismatch. This holds true even for Si substrates which have a lattice mismatch of around 10% with respect to GST. The growth is controlled in situ via line of sight quadrupole mass spectrometer (QMS). Structural characterization is performed in situ by X-ray diffraction (XRD), which reveals a clear cubic symmetry of the film and a lattice slightly rhombohedrally distorted along the [111] direction. INTRODUCTION GST alloys are very promising candidates for future solid state memory technologies due to their fast switching speeds, impressive endurance, and, in particular, excellent scalability as the operating power scales with the active material volume [1]. However, the crystal structure of these materials has not been well analyzed yet because of the lack of single crystals of the metastable cubic phase, which cannot be synthesized in bulk form. In order to understand the detailed switching mechanism of these materials, MBE offers the possibility to grow epitaxial and therefore single crystalline layers of the cubic phase [2-4]. Additionally, the approach of single crystalline growth appears promising as ordered metamaterials require much less energy to be switched from the amorphous to the crystalline state and vice versa [5]. Earlier results of the growth on (001) oriented substrates revealed that due to a rhombohedral distortion of the unit cell, GST films grown on (001) substrates develop significant disorder and a nonplanar growth front [4]. EXPERIMENT The cubic phase change layers were deposited from elemental sources in an MBE chamber. The deposition was controlled in situ by reflection high energy electron diffraction and line of sight QMS, which allows to monitor the atomic or molecular species desorbed from the sample surface during growth. The structure of the layer was controlled by in situ synchrotron XRD at the PHARAO beamline at the BESSY II storage ring. The energy of the x-rays was chosen to be 9.36 keV, far below the Ge K-edge to avoid anomalous scattering effects.
DISCUSSION To allow a reliable control of the MBE growth a QMS has been employed. It is mounted on a source port directly facing the substrate. By periodically opening and closing the shutter in front of the QMS it is possible to confidently account for the background signal, even in dynamically changing situations. The growth window for epitaxial GST (where the crystal quality is best) is unfortunately quite narrow and additionally the growth rate decreases rapidly
Data Loading...
