Self-Ordered Ge Nanodot Fabrication by Using Reduced Pressure Chemical Vapor Deposition

Abstract

Ge nanodot formation on Si surface and its three dimensional alignment is investigated using a reduced pressure chemical vapor deposition system. By exposing GeH 4 on Si (001) surface at 550°C, a smooth wetting Ge layer is deposited for the first ∼0.9 nm, and then Ge nanodot formation occurs according to a Stranski-Krastanov growth mechanism. The Ge nanodots are randomly distributed with density of ∼6 × 10 10 cm −2 . By postannealing at 600°C, the Ge nanodots are coalesced. The size and density become ∼60 nm diameter 5 nm height and ∼1.5 × 10 10 cm −2 , respectively. By exposing GeH 4 followed by postannealing at 600°C on checkerboard mesa structured Si surface which is fabricated by embedded body-centered tetragonal (BCT) Si 0.6 Ge 0.4 nanodots, the Ge nanodot formation occurs at concave regions of the checkerboard mesa. By repeating Ge nanodot formation followed by Si spacer deposition by two step epitaxy using SiH 4 at 600°C and using SiH 2 Cl 2 at 700°C, vertical alignment of the Ge nanodots is observed. The lateral periodicity of the Ge nanodots is the same as that of the BCT Si 0.6 Ge 0.4 nanodot template. The driving force of the self-ordered alignment is tensile strain of Si spacer surface above the Ge nanodots. By using the checkerboard mesa structured Si substrate by embedded BCT Si 0.6 Ge 0.4 nanodot stack deposition as a template, vertically and laterally aligned 3D Ge nanodot stack fabrication is demonstrated without photolithography process.

Heteroepitaxy of group IV materials for future device application

“…Published on behalf of The Japan Society of Applied Physics by IOP Publishing Ltd layer, however, the interface of Si 0.2 Ge 0.8 on Ge is blurred. One of the main reasons for the smeared interface could be the surface segregation of Ge atoms during Si 0.2 Ge 0.8 growth, 33) due to the lower surface energy density of Ge as compared to Si.…”

“…In this case, the driving force of the SiGe nanodot formation is a local tensile strain of Si on the buried SiGe nanodot. 33,34) In the case of 3D-ordered Ge nanodot formation by Ge/ SiGe SL, key parameters for vertical and staggered alignment are also non-uniform local strain and surface roughness of the SiGe spacer. 35,36) By depositing the SiGe spacer at 550 °C, vertical alignment of Ge nanodot is obtained because of smooth SiGe spacer surface formation.…”

“…We summarized a method for abrupt SiGe quantum well (QW) fabrication by C-delta doping, 29) the influence of strain on the surface reaction of heteroepitaxial SiGe growth, 30) and three-dimensional (3D) aligned SiGe and Ge nanodot fabrication by proactively managing strain and surface energies. [31][32][33][34][35][36]…”

Vertical alignment control of self-ordered multilayered Ge nanodots on SiGe

“…By proactively using local tensile strain and surface energy of the Si spacer surface, it is possible to control the following SiGe nanodot formation at on-dot positions or at staggered positions. For the Ge nanodot formation, we have reported dot-on-dot vertically and laterally aligned multilayered Ge nanodots with a Si spacer on SiGe nanodot SL as a template 21) and with a SiGe spacer on a SiGe virtual substrate (VS) without pre-structuring. 22) In this study, we fabricated 3D self-ordered multilayered Ge nanodots on a SiGe VS with SiGe spacers.…”

Three-Dimensional Self-Ordered Multilayered Ge Nanodots on SiGe

“…[1][2][3][4][5][6][7][8][9][10] Many groups studied multilayered Ge nanodots with Si spacers on Si(001) grown by Stranski-Krastanov (SK) growth mode and vertically aligned by local tensile strain induced by buried Ge nanodots. [11][12][13][14][15][16][17] However, to avoid plastic relaxation caused by a 4.2% lattice mismatch between Si and Ge, thick nanodots and/or large layer numbers are challenging. Even though the vertical alignment of the Ge nanodots is realized, the Ge nanodots are randomly distributed in lateral direction.…”