Wanghua Chen

Si-based Nanostructures

Ningbo University

School of Physical Science and Technology, Ningbo University, 315211 Ningbo, China

Email: chenwanghua@nbu.edu.cn

Biography

Abstract for Presentation

Study of GeSn nanowires and Si epitaxial films by PECVD

   In this work, a radio frequency (13.56 MHz) plasma-enhanced chemical vapor (PECVD) reactor is used, where rich structures ranging from nanowires to epitaxial growth have been explored. The first part of this work is devoted to GeSn nanowires (NWs) [1]. Different types of Sn-containing materials were studied [2]. By combing GeH4 plasma and partial reduction of SnO2 particles, we have succeeded in the fabrication of in-plane GeSn NWs reaching an out-of-equilibrium Sn concentration of 22 % with a homogenous incorporation of Sn into the Ge NWs [3]. By changing the NW growth temperature in the range of 160 to 350 ° C, we can adjust the Sn concentration from 22 % to 30 %, and change the Sn atom distribution from core-shell to uniform distribution, while maintaining good NW crystalline quality [4]. We used different annealing conditions to obtain GeSn NWs with different morphologies. Moreover, based on the traditional in-plane solid-liquid-solid (SLS) growth mode, we successfully produced out of plane GeSn NWs by changing the deposition sequence of SnO2 particles and amorphous germanium films, and explored this new growth mode [5]. Moreover, we discovered a new method to grow GeSn nanowires by hydrogen plasma etching of hydrogenated amorphous Ge (a-Ge:H).

   The last part of this work is devoted to the low-temperature Si epitaxial growth. We demonstrate a low-temperature and low-cost process for ultrathin Si solar cells. By taking advantage of the interface porosity controlled by epitaxy growth conditions, we have succeeded in transferring ultrathin epitaxial Si layers and fabricating solar cells based on them [6]. We studied two plasma based surface engineering methods, including deposition of double-layer homogeneous Si epitaxial interface [7] and heterogeneous SiGe epitaxial interface [8].We also study the influence of the deposition rate on the structural properties of epitaxial Si layers. We found that the crystalline quality of epitaxial layers depends on their thickness and deposition rate. Moreover, increasing the deposition rate may lead to epitaxy breakdown. In that case, we observe the formation of embedded amorphous Si cones in the epitaxial layer [9]. Increasing the growth rate is a tricky issue because the agglomeration of clusters required for epitaxy can lead to powder formation in the plasma. We demonstrate that the decisive factor to increase the epitaxial growth rate, i.e. the inhibition of the agglomeration of plasma-born clusters, can be obtained by decreasing the plasma pulse off time or increasing the growth temperature [10]. We have been able to epitaxially grow tetragonal Si on a 4 inch cubic c-Si wafer [11]. We attribute the formation of tetragonal Si to the hydrogenated-cluster-assisted epitaxy.

References

[1] R. Gong, L. Zheng, P. Roca i Cabarrocas, W. Chen, physica status solidi (RRL) – Rapid Research Letters, 16 (2022) 2100554.

[2] L. Zheng, E. Azrak, R. Gong, C. Castro, S. Duguay, P. Pareige, P. Roca i Cabarrocas, W. Chen, Journal of Alloys and Compounds, 899 (2022) 163273.

[3] E. Azrak, W. Chen, S. Moldovan, S. Gao, S. Duguay, P. Pareige, P. Roca i Cabarrocas, The Journal of Physical Chemistry C, 122 (2018) 26236-26242.

[4] E. Azrak, W. Chen, S. Moldovan, S. Duguay, P. Pareige, P. Roca i Cabarrocas, The Journal of Physical Chemistry C, 124 (2020) 1220-1226.

[5] R. Gong, E. Azrak, C. Castro, S. Duguay, P. Pareige, P. Roca i Cabarrocas, W. Chen, Nanotechnology, 32 (2021) 345602.

[6] R. Cariou, W. Chen, I. Cosme-Bolanos, J.-L. Maurice, M. Foldyna, V. Depauw, G. Patriarche, A. Gaucher, A. Cattoni, I. Massiot, S. Collin, E. Cadel, P. Pareige, P. Roca i Cabarrocas, Progress in Photovoltaics: Research and Applications, 24 (2016) 1075-1084.

[7] J. An, Z. Zheng, R. Gong, T.B.T. Nguyen, H. Jun, M. Chrostowki, J.-L. Maurice, W. Chen, P. Roca i Cabarrocas, Applied Surface Science, 518 (2020) 146057.

[8] J. An, J.-L. Maurice, V. Depauw, P. Roca i Cabarrocas, W. Chen, Applied Surface Science, 546 (2021) 149056.

[9] W. Chen, R. Cariou, G. Hamon, R. Léal, J.-L. Maurice, P. Roca i Cabarrocas, Scientific Reports, 7 (2017) 43968.

[10] W. Chen, J.-L. Maurice, J.-C. Vanel, P. Roca i Cabarrocas, Journal of Physics D: Applied Physics, 51 (2018) 235203.

[11] W. Chen, G. Hamon, R. Léal, J.-L. Maurice, L. Largeau, P. Roca i Cabarrocas, Crystal Growth & Design, 17 (2017) 4265-4269.