Metal organic vapor phase epitaxy of Ge1Sb2Te4\hbox {Ge}_{1}\hbox {Sb}_{2}\hbox {Te}_{4} Ge 1 Sb 2 Te 4 thin films on Si(111) substrate

Metal organic vapor phase epitaxy was employed for the growth of homogeneous and coalesced Ge1Sb2Te4 thin films on Si(111) substrate. The influence of substrate pre-annealing on the layer morphology and composition was investigated. The annealing in H2 atmosphere in the presence of Te is important for the deposition of smooth layers. Te atoms passivate Si surface and support van der Waals epitaxy. The growth starts with van der Waals gap followed directly by Ge1Sb2Te4 layer. The morphology of epitaxial material is sensitive to the gas velocity in the reactor during growth. Measured by atomic force microscope, root mean square roughness of grown Ge1Sb2Te4 layers decreases significantly when the total gas flow in the reactor increases from 2100 to 2500 sccm. The layer composition depends strongly on the growth temperature. X-ray diffraction and energy dispersive X-ray spectroscopy confirm that the composition of the material shifts toward lower Ge content with the increase of the growth temperature. The material of the interest, its composition as well as surface morphology, exhibits high sensitivity to the growth conditions

Site-controlled growth of indium nitride based nanostructures using metalorganic vapour phase epitaxy

In this paper we report on studies on how to obtain selective area growth of indium nitride nanostructures on patterned SiO2/GaN(0 0 0 1)/c-plane α-Alα-Al2O3 substrates by means of metalorganic vapour phase epitaxy (MOVPE) for very small pattern filling factors. To this end we investigated the impact of growth parameters such as substrate temperature and the group V/group III molar flow ratio (V/III ratio) on nanostructure morphology and on selectivity. Furthermore we examined the evolution of InN nanostructure growth in 100 nm apertures and the influence of growth stage on the nanostructure's optical characteristics. We found a narrow growth parameter range in which both the reproducible selective growth of InN inside the circular apertures and the parasitic nucleation on the mask were concurrently kept under control. Under these optimized growth conditions we obtained regular, hexagonally shaped nanopyramids which evolved from coalesced nucleation seeds via cauldron-like structures. A systematic study of the nanostructure evolution reveals that the near band edge luminescence depends on the nanostructure growth stage, which is assigned to different strain states and to defect induced free carriers as the InN nanopyramids grow

MOCVD and characterization of GaAs layers on Al pseudo-substrates forfuture ultrafast optoelectronics

GaAs is broadly used in modern electronics. The application of GaAs-based devices in high power electronics, however, is complicated due to the substantial excess heat generated during device operation. One possibility to dissipate the excess heat is to employ substrates with high thermal conductivity. In this contribution we present the growth of GaAs layers by metalorganic vapor phase epitaxy (MOVPE) on aluminum (111) pseudosubstrates designed for an improved heat management in GaAs electronic circuits. They were prepared by Al evaporation on (100) GaAs substrates and subsequent heat treatment. The GaAs layers are polycrystalline. The roughnesses of the layers were in the range of 13 to 62 nm and the thickness in the range of 600 – 2300 nm. The layers exhibit extremely low carrier lifetime due to the growth-induced defects and are suitable for the fabrication of ultrafast metal-semiconductor-metal (MSM) photodetectors (PDs)

Deposition of monocrystalline trigonal Ge_x Sb_y Te_z by Metal Organic Vapour Phase Epitaxy

Phase change memory (PCM) based on chalcogenides such as the Ge-Sb-Te compounds along the Sb2Te3 – GeTe pseudo-binary line have been widely used for optical data storage and in recent years also as nonvolatile resistive memory devices. In these applications, the ultra-fast and reversible phase change between the amorphous and the metastable cubic crystalline phase, associated with a high contrast in reflectivity and resistivity is used for data storage. They are deposited in the amorphous state by atomic layer deposition or physical vapour deposition (sputtering). Due to the lack of applications, the thermodynamically stable crystalline hexagonal phase wasnot in the centre of attention up to now. However, recently superlattices of highly textured hexagonal Sb2Te3 – GeTe layers have received increasing interest due to an altered switching mechanism with reduced switching energy.Switching is field induced and occurs at the interfaces of the materials between two crystalline states circumventing melting for the phase change. The layered structure of monocrystalline hexagonal Ge-Sb-Te inherently resembles the superlattice structure with respect to atomic stacking and crystal orientation to the substrate. For this reason, the preparation and intense study of epitaxial, hexagonal Ge-Sb-Te can be of fundamental interest for future applications. In this contribution, we present the growth and characterization of crystalline Ge-Sb-Te films on Si (111) deposited by MOVPE. At a reactor pressure of 50 hPa and growth temperatures around 450°C epitaxial films are grown using nitrogen as the carrier gas to transport the precursors DETe, TESb and digermane to the reactor. Different partial pressures of the precursors were employed to vary the film composition. The morphology of the deposited material was investigated using AFM and SEM, while the structure of the as-grown samples was studied by XPS, XRD and TEM. The chemical composition was determined using EDS.The two compositions Ge1Sb2Te4 and Ge2Sb2Te5 were controllably achieved. XRD studies indicate, that the 100nm thick Ge-Sb-Te is crystallized in the stable hexagonal structure (P-3m1 or R-3m). TEM investigations reveal that the Ge, Sb and Te atoms form building blocks, consisting of 7 (Ge1Sb2Te4) or 9 (Ge2Sb2Te5) alternating cation and anion layers in parallel to the Si (111) substrate surface, stacked along the [0001] axis. These building blocks are separated by van der Waals gaps originating from hexagonal Sb2Te3, where they are naturally present. The samples are monocrystalline and exhibit a low amount of defects. XPS reveals oxidation mainly of Ge and Sb at the surface of the films. Additionally the occupation of the cation sites by Ge and Sb atoms in the hexagonal lattice was investigated by TEM and XPS

Metal organic chemical vapor deposition of GexSbyTez layers grown by using digermane

GexSbyTez (GST) films grown on Si(111) substrates by epitaxy tend to be polycrystalline and therefore rough. Especially the incorporation of Germanium in the films is problematic. Thin and smooth film surfaces are however a prerequisite for memory applications. In the past we demonstrated that the metal organic chemical vapor deposition (MOCVD) growth of highly mismatched III/V materials such as InAs/GaAs can be accomplished conformally, if a low temperature growth process is used. This knowledge is transferred to MOCVD growth of GST. To this end as a Ge precursor digermane was employed which is expected to decompose at low temperatures. Commercial sources for Sb (triethylanthimony) and Te (diethyltellur) were chosen, which are suitable for low temperature deposition. At first the growth of Sb2Te3 layers was optimized. Than digermane was added to the growth process. Growth was evaluated by SEM, XRD and Raman measurements. It was found that GST can be deposited at the same conditions as Sb2Te3. SEM pictures show well coalesced, trigonal crystalline structures and XRD measurements verify the integration of Ge. The influence of growth parameters on layer growth will be presented