Rare-earth-metal oxide buffer for epitaxial growth of single crystal GeSi and Ge on Si(111)

Abstract

Ternary and binary rare-earth oxides that are used as a template buffer, which accommodates the crystal lattice mismatch between substrate and a semiconductor layer, are discussed here. The oxides were grown on Si(111) substrates and exhibit the cubic bixbyite crystal structure. Stabilization of the cubic bixbyite structure of ternary erbium-neodymium oxide and lanthanum oxide was analyzed using structural investigation of the epitaxially grown oxides and ab initio density functional theory calculations. The authors demonstrate that despite the more energetically favorable hexagonal structure of bulk lanthanum oxide a pseudomorphic single crystal cubic lanthanum oxide layer grows under nonequilibrium conditions of a molecular beam epitaxy process on gadolinium oxide. Growth of hexagonal lanthanum oxide begins when the critical thickness of the layer is reached. Germanium was epitaxially grown on the cubic bixbyite lanthanum sesquioxide. Due to a higher surface energy, germanium starts to grow in the form of twinned islands on the oxide layer that later merge, forming a closed layer. X ray diffraction reveals mostly single crystal structure of the germanium layer with stacking twins located only at the interface with the lanthanum oxide layer.

Epitaxial Si and Gd2O3Heterostructures: Distributed Bragg Reflectors with Stress Management Function for GaN on Si Light Emitting Devices

“…It was shown in other studies 8,13,14 that rare-earth sesquioxides with a cation radius smaller than samarium have stable cubic bixbyite structure at temperatures below 1000 • C. Among those, at room temperature, the lattice constant of gadolinium oxide is only 0.5% smaller than twice that of silicon and this makes it an appropriate material for growth on Si. Currently, the industry is using GaN layers grown along the c-axis which coincides with the b-axis of the cubic structure.…”

“…3 Many groups are working on implementation of a buffer layer that would manage the lattice mismatch in the structure and subsequently would reduce the resulting strain in a final stresscompensated wafer that is meeting the industry specified bow limits for 200 mm diameter wafers of 50 μm. [3][4][5][6][7] Rare earth oxides have already proven to be suitable as a template buffer layer for silicon-oninsulator and germanium-on-insulator structures 8,9 due their excellent crystal and chemical stability at typical processing temperatures. From this group of materials, gadolinium oxide is of particular interest because it is suitable as a candidate material for stress engineered buffer layers due to its close lattice matching to twice that of silicon.…”

Epitaxial Si and Gd2O3 Heterostructures - Distributed Bragg Reflectors with Stress Management Function for GaN on Si Light Emitting Devices

“…It was shown in other studies (8,13,14) that rare-earth sesquioxides with a cation radius smaller than samarium have stable cubic bixbyite structure at temperatures below 1000˚C. Among those, at room temperature, the lattice constant of gadolinium oxide is only 0.5% smaller than twice that of silicon and this makes it an appropriate material for growth on Si.…”

“…Many groups are working on implementation of a buffer layer that would manage the lattice mismatch in the structure and subsequently would reduce the resulting strain in a final stresscompensated wafer that is meeting the industry specified bow limits for 200 mm diameter wafers of 50 m (3)(4)(5)(6)(7). Rare earth oxides have already proven to be suitable as a template buffer layer for silicon-on-insulator and germanium-on-insulator structures (8,9) due their excellent crystal and chemical stability at typical processing temperatures. From this group of materials, gadolinium oxide is of particular interest because it is suitable as a candidate material for stress engineered buffer layers due to its close lattice matching to twice that of silicon (10).…”

Oxygen-Deficient Oxide Growth by Subliming the Oxide Source Material: The Cause of Silicide Formation in Rare Earth Oxides on Silicon

“…In principle, two different growth schemes can be used for the oxide growth by MBE, or analogous deposition techniques. First is the thermal evaporation of the rare-earth metal with simultaneous addition of oxygen to form the oxide on the heated Si substrate, − which allows a relatively low source temperature for the metal evaporation. This scheme bears the risk of detrimental effects of the free oxygen, such as formation of a parasitic SiO 2 interface layer, the degradation of hot filaments in the growth chamber, and the risk of silicide formation by reaction of the rare earth metal vapor with the heated silicon .…”