Erdem Arkun

Study of thermal stability of distributed Bragg reflectors based on epitaxial rare-earth oxide and silicon heterostructures

Thermal stability of rare-earth oxide/silicon multilayer heterostructure-based distributed Bragg reflectors under typical metal organic chemical vapor deposition process temperatures with an ambience of typical process gases was studied. Gadolinium oxide or erbium oxide based two period (¼λ oxide, ¾λSi) blue light (λ = 450 nm) mirrors with Si layer on the top were annealed in H2, N2, and H2 + NH3 gases for 20 min at 1015 °C in a metal organic chemical vapor deposition chamber. Changes in the structure were analyzed using x-ray diffraction and transmission electron microscopy. Reflectivity measurements were used for evaluation of optical properties of the reflectors before and after annealing. Chemical reaction between gadolinium oxide and silicon are revealed by reduction of reflectivity of Gd2O3/Si based distributed Braggs reflector and GdSi2-x attributed peaks detected by x-ray diffraction. No major changes were detected in the Er2O3/Si heterostructure-based reflector, indicating good chemical and crys...

Study of the Structural and Thermal Properties of Single Crystalline Epitaxial Rare-Earth-Metal Oxide Layers Grown on Si(111)

Rare-earth-metal oxides (REO) grown epitaxially on silicon have attracted much attention because of their applications as gate dielectrics for MOS devices or as a buffer layer for epitaxial high carrier mobility semiconductor growth on silicon. Some of the oxides have stable cubic crystal structures and are suitable for growth on silicon. However, their crystal lattice is smaller if compared to that of twice that of silicon (from 0.5 % for Gd2O3 to 4.2% for Lu2O3). Stress and dislocations appearing at the interface and in the oxide layer influence the electronic band structure (it is of importance for REOs application as gate dielectric) and structure of a high mobility semiconductor layer if grown on the top of the oxide. Additionally, the thermal expansion coefficient of the bulk oxides is higher than that of silicon. For this reason, control of thermal stress in the REO-silicon structure is of high importance. In this work, results of thermal stress studies of REO layers epitaxial grown by molecular beam epitaxy (MBE) on Si(111) substrates are presented. In contrast to the similar works published earlier [1],[2] that investigated thermal stress in nanometer thick (up to 20 nm) oxide layers grown on silicon substrates, the thickness of the oxide layers in this study is in range from 100 nm to 500 nm. This is a typical thickness used for buried dielectric layer for semiconductor on isolator (SOI) structures. The stress behaviour in such “thick” layers is expected to be different from that in the thin layers. Additionally, the poor thermal conductivity of thermal silicon dioxide as a buried dielectric layer in SOI structure and the self-heating effects in CMOS devices is one of the most important factors that motivate looking for alternative dielectric materials. There is very little data in the literature of the thermal conductivity of bulk rareearth-metal oxides and no data about the thermal conductivity of single crystalline thin REO layers. The gadolinium oxide and erbium oxide layers were grown in an MBE system by the evaporation of the metals from effusion cells and molecular oxygen from a gas manifold. The crystal structure and thermal stress of the layers were investigated using high resolution X-ray diffractometer with in-situ heating of a sample up to 1000 C temperature in nitrogen ambience. The time-domain thermoreflectance method [3] was used for measurement of thermal conductivity of the REO layers. Results of the structure analysis of rare-earth metal – oxide layers grown on silicon show that at room temperature, the gadolinium oxide (and erbium oxide) inplane and out of plane crystal lattice parameters are similar whithin the error limits indicating an almost fully relaxed cubic lattice (Fig. 1). On the other hand, an increase of the out of -plane lattice constant with oxide thickness is clearly seen (Fig.2). This could be explained by minor tetragonal distortion of the oxide lattice [4]. However in our case, the oxide lattice is under tension in the in-plane direction which should result in a decrease of the out of-plane lattice constant. This distortion is more notable for thinner layers.

Growth of Epitaxial Silicon-on-Insulator Substrates by Solid State Epitaxy

Single step growth of crystalline silicon on insulator (c-SOI) substrates based on rare earth oxide (REO) insulator layers are presented. Growth of crystalline REOs on silicon is possible due to their unique lattice matching to twice the lattice spacing of silicon. The single crystal nature of REOs make further silicon overlayer growth with moderate defect densities possible. In this paper we present the growth of Gd<inf>2</inf>O<inf>3</inf> and (Er<inf>x</inf>Nd<inf>1−x</inf>)<inf>2</inf>O<inf>3</inf> on silicon (111) substrates by solid state epitaxy. Silicon overlayers grown by e-beam evaporation on Gd<inf>2</inf>O<inf>3</inf> single crystal films exhibit specular and shiny surfaces conducive for further growth of silicon by chemical routes. Chemical vapor deposition (CVD) growth of silicon on top of the e-beam evaporated template layers were grown at 1150°C. Samples were characterized by AFM, TEM and X-ray diffraction.