PECVD grown Ge nanocrystals embedded in : From disordered to templated self-organization
Introduction
In the last decade, Ge nanocrystals (NCs) embedded in have attracted considerable research interest due to possible applications in optoelectronic [1] and non-volatile memory devices [2]. Different types of self-organization processes have been investigated for the preparation of the Ge NCs in order to achieve high NC areal densities and small average NC diameters. The application of NCs in progressively downscaled electronic devices require a defined number of equal-sized NCs per device to avoid large fluctuations in the device characteristics and an exact alignment of the position of NCs with respect to neighboring structures as, e.g., electrical contacts. Self-organization, however, is usually accompanied by random vertical and/or lateral positions of the NCs, by local fluctuations of the NC areal density, by significant size variations of the NCs, and by a high sensitivity to process parameters. Up to now, only a few reports have addressed this important issue [3], [4].
In this work, we used self-organization during rapid thermal annealing to transform a continuous ultra-thin (2–3 nm) layer of amorphous Ge sandwiched between a bottom and a top layer into isolated NCs [5]. Driving mechanisms of this self-organization process are homogeneous crystal nucleation and the endeavor to minimize the interface [6]. By a combination of this bottom-up approach with the top-down approach of nanostructuring, we succeeded in achieving an exact definition of the vertical and lateral NC position and of the NC size. For nanostructuring, nanoimprint patterning [7], [8] was used since this method combines the ability to create sub 25 nm structures with the possibility of rapid patterning of large areas [9].
Section snippets
Experimental
Continuous Ge layers with a thickness of 2.3 nm were deposited by plasma enhanced chemical vapor deposition (PECVD) at 200 °C onto 4 nm layers, thermally grown on Si (1 0 0) substrates. They were subsequently capped in situ with 12 nm PECVD films deposited at 400 °C. Therefore, the vertical NC position was determined and any exposure of the Ge to detrimental ambient influences was avoided. Fig. 1(a) shows a cross section TEM image of the as-prepared layer stack. Annealing these unstructured
Results and discussion
The PDMS mold was equipped with arrays of circular pits predefining the Ge reservoirs. Different reservoir areas with diameters , 60, and 80 nm were investigated which were arranged in a simple cubic pattern with periods of , and 240 nm, respectively. Fig. 3 shows the successful transfer of the structures after nanoimprint patterning and removal of the excessive areas of the layer stack by RIE. The inset shows a schematic of the cross section along .
In order to ensure the
Conclusion
A promising new “templated self-organization” method has been presented which combines a bottom-up and a top-down approach for the preparation of equal-sized Ge NCs in with well-defined vertical and lateral positions. In order to predefine Ge reservoirs for each NC, a layer stack consisting of an amorphous Ge layer embedded between a bottom and a top was structured by nanoimprint patterning. This method combines high resolution and rapid patterning. By thermal annealing, each Ge
References (13)
- et al.
PE-CVD fabrication of germanium nanoclusters for memory applications
Mat. Sci. Eng. B
(2008) - et al.
Status and prospects of UV-nanoimprint technology
Microelectron. Eng.
(2006) - et al.
Improved mold fabrication for the definition of high quality nanopatterns by Soft UV-nanoimprint lithography using diluted PDMS material
Microelectron. Eng.
(2007) - et al.
Highly selective HBr etch process for fabrication of triple-gate nano-scale SOI-MOSFETs
Microelectron. Eng.
(2004) Visible photoluminescence from nanocrystallite Ge embedded in a glassy matrix: evidence in support of the quantum-confinement mechanism
Phys. Rev. B
(1995)- et al.
Charge trap memory device fabricated by oxidation of
IEEE Trans. Electron Devices
(2001)
Cited by (5)
Low temperature deposition of germanium on silicon using Radio Frequency Plasma Enhanced Chemical Vapor Deposition
2017, Thin Solid FilmsCitation Excerpt :The incorporation of hydrogen helps in etching the week bonds in the Ge-Ge network, which promotes the generation of a prolong chain of crystalline order. Furthermore, RF-PECVD reactor promotes the nanocrystal growth at low temperature via plasma contribution [28,29]. Fig. 4e shows the contrast appear in the diffraction pattern for the low and the high temperature Ge layer which related to the different GeH4 flow rates in each layer.
Preparation induced electrical behaviour of GeSiO nanostructures
2011, Proceedings of the International Semiconductor Conference, CASInfluence of preparation method on structural properties of GeSiO nanosystems
2010, Proceedings of the International Semiconductor Conference, CASControlled growth morphology of porous nanocrystal iron oxide by electrodeposition
2009, Chemical Research in Chinese Universities
- 1
Current address: Department of Physics, Harvard University, Cambridge, MA 02138, USA.