Daniela Cavalcoli

TESI per Laurea Magistrale in Physics, Curriculum MANO.

1. Advanced semiconductor thin films for sensor applications.

Innovative perovskites thin films are becoming more and more attracting for several applications. In particular, methylammonium lead iodide perovskite (CH3NH3PbI3) has recently demonstrated to be a very interesting material applications in solar cells and radiation sensors applications [1,2]. However, notwithstanding encouraging results in applications, perovskites still suffer from stability problems when used as transport layer in thin film solar cells, and one of the possible causes of the stability issue should be found in the presence of defect states [3,4].

The research activity aims to monitor defect states and compositional changes of the perovskite layers. The analyses will be carried out by electrical and optical characterization methods (temperature dependent current-voltage and capacitance voltage analyses), charge spectroscopy techniques (Deep Level Transient Spectroscopy, Photo induced transient spectroscopy) and Surface Photovoltage Spectroscopy.

The activity will be carried out in at the Bologna Semiconductor Physics Group of the Physics and Astronomy Dept. Internships abroad are also available on request. For further information on the research activity please visit the group website [5].

1. M. A. Green, A. Ho-Baillie, H. J. Snaith, The emergence of perovskite solar cells. Nat. Photonics 8, 506–514 (2014). 10.1038/nphoton.2014.134
2. Haotong Wei, Yanjun Fang, Padhraic Mulligan, William Chuirazzi, Hong-Hua Fang, Congcong Wang, Benjamin R. Ecker, Yongli Gao, Maria Antonietta Loi, Lei Cao & Jinsong Huang; “Sensitive X-ray detectors made of methylammonium lead tribromide perovskite single crystals” Nature Photonics volume 10, pages 333–339 (2016)
3. Sung Heo, Gabseok Seo, Yonghui Lee,c, Dongwook Lee, Minsu Seol, Jooho Lee, Jong-Bong Park, Kihong Kim, Dong-Jin Yun, Yong Su Kim, Jai Kwang Shin, Tae Kyu Ahn and Mohammad Khaja Nazeeruddin, “Deep level trapped defect analysis in CH3NH3PbI3 perovskite solar cells by deep level transient spectroscopy” Energy Environ. Sci., 10, 1128, (2017).
4. Sung HeoGabseok SeoYonghui LeeMinsu SeolSeong Heon KimDong‐Jin YunYongsu KimKihong KimJunho LeeJooho Lee,Woo Sung JeonJai Kwang ShinJucheol ParkDongwook Lee Mohammad Khaja Nazeeruddin; “Origins of High Performance and Degradation in the Mixed Perovskite Solar Cells” Adv Mater. 2019.
5. https://site.unibo.it/semiconductor-physics/en
   
   

2. III-N semiconductor alloys and compounds

III-Nitride alloys uniquely offer tuning of their bandgap from infra-red (0.7 eV) to ultra-violet (6.1 eV) as well as strong anisotropic polarization reaching as high as 0.081 C/m². Thanks to their high thermal and mechanical stability, Al_xGa_1-xN and In_xGa_1-xN based optoelectronic devices have already approached commercial applications. While white, blue and ultra-violet light emitting diodes (LEDs) are well-known examples [1], AlGaN/GaN based high electron mobility transistors [2] are considered serious contenders for replacing vacuum tubes in radio-frequency (RF) electronics for multitude of applications. Apart from light emitting applications, In_xGa_1-xN-based structures might as well be highly promising for THz detection based on inter-subband absorption in the quantum wells and for multijunction solar cells in tandem with Si [3]. However, special attention towards the material characteristics is required, as fundamental material issues still need to be understood and resolved.

The research activity proposed aims to advance the fundamental knowledge on these materials alloys, on the role of defects, strain, doping on the electronic properties of the materials and devices. The thesis is carried out in cooperation with the IMEC Institute in Belgium. https://www.imec-int.com/en/home.

Further details on the thesis project can be found here:

Quantitative 3D mapping of carrier concentration in quantum-confined heterostructures for power and RF applications [https://www.imec-int.com/en/work-at-imec/job-opportunities/quantitative-3d-mapping-of-carrier-concentration-in-quantum-confined-heterostructures-for-power-and-rf-applications]

https://www.imec-int.com/en/work-at-imec/academic-opportunities?employmenttypes=1106

Tutor at IMEC: Albert Minj.

[1] T. Lin, Z.Y. Zhou, Y.M. Huang, K. Yang, B.J. Zhang, Z.C. Feng, Strain-Controlled Recombination in InGaN/GaN Multiple Quantum Wells on Silicon Substrates, Nanoscale Res. Lett. 13 (2018). doi:10.1186/s11671-018-2663-6.

[2] U.K. Mishra, P. Parikh, Y.F. Wu, AlGaN/GaN HEMTs - An overview of device operation and applications, Proc. IEEE. 90 (2002) 1022–1031. doi:10.1109/JPROC.2002.1021567.