【日時】

2016年11月4日(金) 15:00～1時間程度

 

【場所】

東北大学 流体科学研究所 2号館 5階 大会議室「西」

（宮城県仙台市青葉区片平2-1-1） （地図）

 

 

Speaker:

Dr. Sergii Tutashkonko (Designated Assistant Professor, Nagoya University)

 

Title:

Engineering Si and Ge self-assembled nanostructures: where chemistry and physicscome along

 

Abstract:

In the first part of the talk, I will present the method to realize semiconductor nanostructures by electrochemical porosification. Appearance of pores induces new properties to the semiconducting materials such as Si and Ge. In the case of the macroporous materials, the structuring modifies the mechanical properties and increases the specific surface area. The reduction to nanoscale leads to a quantization of electronic and optical properties of the material. Moreover, drilling the semiconducting material with columnar crystallographic mesopores transforms it into a material with strongly anisotropic properties, providing a path to its application to birefringent dichroic filters and photonic crystals.

 

Porous Si is a well know and well-studied material. Although Ge is the principal semiconductor for optoelectronic applications, until recently the formation of nano- and meso-porous Ge (pGe) by a commonly-used electrochemical etching technique was not possible. The main issue for Ge porosification was the insufficient passivation of Ge due to instability of its oxide. During the seminar, I will present a process to realize thick nano- and meso-porous Ge layers with ordered pores of tunable morphology which was developed in the frame of my PhD thesis. In addition I will present the study of composition of porous Ge network at nanolevel, analysis of optical and thermal properties and its reconstruction during high-temperature annealing.

 

In the second part of the talk, I will present a method to realize vertical Ge/Si nanopillars by maskless etching of Ge quantum dot nanostructures The method consists of growing one layer of Ge quantum dot (QD) on Si substrate by gas-source molecular beam epitaxy and consecutive anisotropic etching of material around QDs with KOH. By growing the structures on (110)-oriented Si substrates, the etching profile is made vertical, since the stopping <111> planes for KOH etch are normal to the surface. The resulting structures are mushroom-shaped with Si “stems” and Ge “caps”.

 

In the third part of the talk, I will make a discourse to aluminum-induced crystallization (AIC) of amorphous Si. The AIC method consists in depositing the polycrystalline Al and amorphous Si layers and consecutive annealing below the eutectic temperature of Al/Si alloy=577°C. The use of such a poly-Si layer as a seed for epitaxial thickening imposes strict requirements on the grain size, crystalline orientation control, continuity and surface roughness of thin films. Fine-tuning of the AIC process to achieve epitaxy-friendly substrates is a key point of my report.