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Physics Seminar

Modern Device Concepts based on novel aspects in the MBE of classic wide gap II-VI semiconductors

Speaker: Alexander Pawlis (Peter Grunberg Institute Forschungszentrum Julich GmbH)
Date: Wednesday 15 February 2023
Time: 15:00
Venue: Queens Building N3.28

The classic II-VI semiconductors (ZnSe, MgSe, CdSe) and their alloys have been intensively investigated in the 1980-2000 focusing on the development of blue and green lasers. After many efforts it became clear that these materials are not suited for such high-current/high-power applications, due to severe problems in the realization of low-resistive non-degenerating n- and p-type ohmic contacts. However, the classic II/VI compounds offer enormous potential for application as modern quantum devices, where other material properties are more important: Featuring excellent and homogeneous crystallographic properties of molecular beam epitaxy (MBE) grown heterostructures, high oscillator strength of the optical transitions, the possibility of isotope engineering and the availability of sophisticated in-situ nanofabrication techniques. All these aspects can be fulfilled by the classic II/VI semiconductors, which makes them highly attractive to implement building blocks for solid-state quantum information technology such as single-photon sources and optically- or electrically-controlled spin qubits. However, harvesting these excellent material properties in an optimal way for the realization of quantum devices requires the development of novel, unconventional approaches for the MBE growth as well as advanced in-situ nanofabrication techniques of II-VI semiconductor devices. In this context, I will briefly introduce novel approaches in order to reshape the II-VI materials for potential applications as modern quantum devices. Besides the MBE growth of sophisticated heterostructures I will highlight MBE growth of isotopically purified 64Zn80Se [1] and in-situ 3D-nanostructure growth. The second part of my talk is focused on the realization of single-photon sources and spin qubits utilizing halogenide (F,Cl)-doped ZnSe quantum wells for which we have set several benchmarking milestones over the past decade. This includes the demonstration of indistinguishability between two individual single-photon emitters [2], generation of two-photon polarization-entangled quantum states [3] and optical initialization/read-out of a single ZnSe-F qubit [4]. More recent investigations turned out that ZnSe-Cl qubits are even more attractive as qubits as Cl allows for better doping control and superior lattice incorporation on a Se site. Here we recently demonstrated the enhancement of the quantum efficiency of ZnSe-Cl single-photon sources by sophisticated microlenses [5] and verified biexciton-exciton cascaded emission from those sources [6], which makes them promising for entangled-photon pair emission. All these findings demonstrate the broad potential of the classic wide gap II/VI semiconductors for application in state-of-the-art quantum information technology. Finally, I briefly present our recent success on the development of low-resistive ohmic contacts to n-type ZnSe-Cl with linear current-voltage characteristics at room temperature and especially at 4 K [7], tackling one of the most challenging and remaining open issues for ZnSe. Having solved this obstacle, we now follow the route towards the development of advanced electrical devices such as low-temperature operated field-effect transistors and electrostatically defined quantum dots. The latter can be utilized as all-electrical spin qubits, where ZnSe and related compounds can unite the main advantages of to- date established systems like the group-IV and III-V semiconductors. [1] A. Pawlis, G. Mussler, C. Krause, B. Bennemann, U. Breuer, D. Grützmacher, ACS Appl. Electron. Mater. 1, 44 (2019). [2] K. Sanaka, A. Pawlis, T. D. Ladd,1 K. Lischka, Y. Yamamoto, Phys. Rev. Lett. 103, 053601 (2009). [3] K. Sanaka, A. Pawlis, T.D. Ladd, D. J. Sleiter, K. Lischka, Y. Yamamoto, Nano Letters 12, 4611 (2012). [4] D. J. Sleiter, K. Sanaka, M. Kim, K. Lischka, A. Pawlis, Y. Yamamoto, Nano Letters 13, 116 (2013). [5] Y. Kutovyi, M. M. Jansen, S. Qiao, C. Falter, N. von den Driesch, T. Brazda, N. Demarina, S. Trellenkamp, B. Bennemann, D. Grützmacher, A. Pawlis, ACS Nano 16, 14582 (2023). [6] R. M. Pettit, A. Karasahin, N. von den Driesch, M. M. Jansen, A. Pawlis, E. Waks, Nano Letters 22, 9457 (2022). [7] J. Janßen, F. Hartz, T. Huckemann, C. Kamphausen, M. Neul, L.R. Schreiber, A. Pawlis, ACS Appl. Electron. Mater. 2, 898 (2020).