Research
Our research group works at a boundary between two disciplines: surface (or interface) physics and semiconductor technology, attempting to build up a connection between them. We combine surface-sensitive and opto-electrical measurements of semiconductor component interfaces in experiments, while detailed atomic and electronic structures of solids are connected to macroscopic electrical properties in simulations. During the last 30 years, we have focused on traditional semiconductor materials (e.g. Si, Ge, III-V, SiC) which are used in the current industry.
In the preparation and characterization of semiconductor surfaces, we combine wet chemical cleaning and different treatments in ultra-clean environment of ultrahigh-vacuum (UHV) chambers, which include low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and x-ray photoelectron spectroscopy (XPS) measurement methods. We have also obtained experience from using high-resolution synchrotron-radiation photoelectron spectroscopy to reveal detailed atomic bonding sites which remain hidden in the common laboratory-based XPS measurements. To connect the interface chemical, electronic, and structural properties to the opto-electrical ones, we develop own skills to manufacture and characterize simple semiconductor devices (e.g. Schottky diodes and metal-oxide-semiconductor capacitors) in clean rooms of the University of Turku.
In the computational side, the group has obtained strong expertise to combine various simulation programs, starting from quantum mechanical density-functional-theory calculations, which provide detailed atomic and electronic structures that are very difficult to measure in practice. To simulate larger material systems, molecular-dynamics LAMMPS code is used, and open simulation programs are used for simulating electrical properties such as an effective resistivity of a semiconductor-based object and losses in electromagnetic signal propagation.
By combining the simulation and experiments, we aim to advance atomic-level understanding and engineering of the semiconductor interface properties that are closely linked to practical challenges in the current semiconductor industry.
Examples of research interests:
– Properties of oxidized semiconductor surfaces,
– Electronic and electrical properties of poly-crystalline Si films,
– Formation of Ohmic metal-semiconductor interface,
– Surface cleaning and passivation methods,
– Surface doping n-type or p-type,
– Development of UHV instruments for larger use,
– Manufacturing processes of semiconductor devices.
Three examples of group’s activities
Oxidation of semiconductor surfaces: At most semiconductor surfaces, incorporation of oxygen atoms is an energetically driven process which is very difficult to avoid and control in practice on atomic level. Probably every semiconductor device includes oxygen atoms at its surface and interface regions, but the resulting changes in physicochemical properties of device materials are not understood properly. It is surprisingly difficult to observe oxygen atoms even with the most surface-sensitive measurements at initial stages of the oxidation. Concerning this challenge, we have seen that STM provides irreplaceable information, while ab initio calculations are needed to understand changes in the atomic and electronic structures. Please see the selected articles:
M. P. J. Punkkinen, P. Laukkanen, J. Lång, M. Kuzmin, M. Tuominen, V. Tuominen, J. Dahl, M. Pessa, M. Guina, K. Kokko, J. Sadowski, B. Johansson, I. J. Väyrynen, and L. Vitos: Oxidized In-containing III-V(100) surfaces: Formation of crystalline oxide films and semiconductor-oxide interfaces. Physical Review B 83 (2011) 195329.
J. K. Lång, M. P. J. Punkkinen, M. Tuominen, H.-P. Hedman, M. Vähä-Heikkilä, V. Polojärvi, J. Salmi, V.-M. Korpijärvi, K. Schulte, M. Kuzmin, R. Punkkinen, P. Laukkanen, M. Guina, and K. Kokko: Unveiling and controlling the electronic structure of oxidized semiconductor surfaces: crystalline oxidized InSb(100)(1×2)-O. Physical Review B 90 (2014) 045312.
J. Mäkelä, M. Tuominen, J. Dahl, S. Granroth, M. Yasir, J.-P. Lehtiö, R.-R. Uusitalo, M. Kuzmin, M. P. J. Punkkinen, P. Laukkanen, K. Kokko, R. Felix, M. Lastusaari, H.-P. Hedman, R. Punkkinen, J. Lyytikäinen, V. Polojärvi, A. Tukiainen, and M. Guina: Decreasing defect-state density of Al2O3/Ga(x)In(1-x)As device interfaces with InOx structures. Advanced Materials Interfaces 4 (2017) 1700722.
J. Mäkelä, Z. Jahanshah Rad, J.-P. Lehtiö, M. Tuominen, J. Dahl, M.Kuzmin, M. P. J. Punkkinen, P. Laukkanen, and K. Kokko: Crystalline oxide phases on InSb(111)B revealed with scanning tunneling microscopy and spectroscopy. Scientific Reports 8 (2018) 14382.
M. Kuzmin, J.-P. Lehtiö, J. Mäkelä, M. Yasir, Z. Jahanshah Rad, E. Vuorinen, A. Lahti, M. Punkkinen, P. Laukkanen, K. Kokko, H.-P. Hedman, R. Punkkinen, M. Lastusaari, P. Repo, and H. Savin: Observation of Crystalline Oxidized Silicon Phase. Advanced Materials Interfaces 6 (2019) 1802033.
Z. J. Rad, J.-P. Lehtiö, I. Mack, K. Rosta, K. Chen, V. Vähänissi, M. Punkkinen, R. Punkkinen, H.-P. Hedman, A. Pavlov, M. Kuzmin, H. Savin, P. Laukkanen, and K. Kokko: Decreasing Interface Defect Densities via Silicon Oxide Passivation at Temperatures Below 450 °C. ACS Applied Materials & Interfaces 12 (2020) 46933.
Z. J. Rad, M. Miettinen, R. Punkkinen, P. Suomalainen, M. Punkkinen, P. Laukkanen, and K. Kokko: Potential of ultrahigh-vacuum based surface treatments in silicon technology. Microelectronic Engineering 300 (2025) 112382.
D. Srivastava, A. Lahti, K. Kokko, M. Punkkinen, and P. Laukkanen: Atomic-Level Insights Into the Initial Oxidative Crystallization of Si(100) to Periodic SiOx. Advanced Theory and Simulations 9 (2026) e01781.
Properties of poly-crystalline silicon films: Poly-crystalline Si films have been widely used in current microelectronics and photonics devices (e.g. transistors, solar cells), but much less is known about their physical properties as compared to mono-crystalline wafers, because grain boundaries significantly affect the properties of poly-Si. Our group has investigated these properties together with the semiconductor industry to develop an understanding of poly-Si films from atomic-level properties all the way to macroscopic electrical properties. Research topics have focused particularly on substrate losses and electromagnetic signal interference in microcircuits. The main computational methods include first-principles electronic structure, classical molecular dynamics, and device and circuit simulation methods.
M. Santonen, A. Lahti, Z. Rad, M. Miettinen, M. Ebrahimzadeh, J.-P. Lehtiö, P. Laukkanen, M. Punkkinen, P. Paturi, K. Kokko, A. Kuronen, W. Li, L. Vitos, K. Parkkinen, and M. Eklund: Polycrystalline silicon, a molecular dynamics study: Part I – Deposition and growth modes. Modelling and Simulation in Materials Science and Engineering 32 (2024) 065025.
A. Lahti, M. Santonen, Z. Rad, M. Miettinen, M. Ebrahimzadeh, J.-P. Lehtiö, P. Laukkanen M. Punkkinen, P. Paturi, K. Kokko, A. Kuronen, W. Li, L. Vitos; K. Parkkinen, and M. Eklund: Polycrystalline silicon, a molecular dynamics study: Part II – Grains, grain boundaries and their structure. Modelling and Simulation in Materials Science and Engineering 32 (2024) 065026.
M. Santonen, A. Lahti, D. Srivastava, Z. J. Rad ,M. Miettinen, M. Ebrahimzadeh, J. Laaksonen, P. Laukkanen, M. Punkkinen, K. Kokko, A. Kuronen, K. Parkkinen, and M. Eklund, Modeling the Influence of Deposition Parameters on the Crystalline Degree in the Simulations of Polycrystalline Silicon. Physica Status Solidi B: Basic Solid State Physics 262 (2025) 2400483.
M. Santonen, A. Lahti, Z. J. Rad, M. Miettinen, M. Ebrahimzadeh, J.-P. Lehtiö, E. Snellman, P. Laukkanen, M. Punkkinen, K. Kokko, K. Parkkinen, and M. Eklund: A detailed examination of polysilicon resistivity incorporating the grain size distribution. IEEE Transactions on Electron Devices 72 (2025) 1184.
Doping of semiconductor surfaces: n-type and p-type doping of semiconductor surfaces is a prerequisite for manufacturing low-resistive Ohmic metal-semiconductor contacts for various devices. It is challenging to change the doping level of semiconductor surfaces in a controlled way on nanometer or even atomic scale. Furthermore, semiconductor surfaces are very defect rich in general, and the interplay between the doping atoms and surfaces defects is not understood. The resulting concentration of electron or hole electric carriers at interfaces might be very different from the known bulk carrier concentrations. One of our aims is to understand such surface-induced changes in the doping and to develop methods for controlling the surface doping.
J. Mäkelä, M. Tuominen, T. Nieminen, M. Yasir, M. Kuzmin, J. Dahl, M.P.J. Punkkinen, P. Laukkanen, K. Kokko, J. R. Osiecki, K. Schulte, M. Lastusaari, H. Huhtinen, and P. Paturi: Comparison of chemical, electronic, and optical properties of Mg-doped Al0.5Ga0.5N. Journal of Physical Chemistry C 120 (2016) 28591.
M. Yasir, J. Mäkelä, D. Koiva, M. Tuominen, J. Dahl, J.-P. Lehtiö, M. Kuzmin, Z. Jahanshah Rad, M. Punkkinen, P. Laukkanen, K. Kokko, V. Polojärvi, J. Lyytikäinen, A. Tukiainen, and M. Guina: Surface doping of GaxIn1-xAs semiconductor crystals with magnesium. Materialia 2 (2018) 33.
M. Ebrahimzadeh, S. Granroth, S. Vuori, M. Punkkinen, M. Miettinen, R. Punkkinen, M. Kuzmin, P. Laukkanen, M. Lastusaari, and K. Kokko: Wet Chemical Treatment and Mg doping of p-InP Surfaces for Ohmic Low-Resistive Metal Contacts. Advanced Engineering Materials 25 (2023) 2300762.
M. Miettinen, E. Vuorinen, J.-P. Lehtiö, Z. J. Rad, R. Punkkinen, M. Kuzmin, J. Järvinen, V. Vähänissi, P. Laukkanen, H. Savin, and K. Kokko: Effects of different surface cleaning methods on n-type silicon contact resistivity. Applied Surface Science 695 (2025) 162790.
M. Miettinen, V. Nuutila, Z. J. Rad, M. Ebrahimzadeh, A. Ruokonen, R. Punkkinen, J.-P. Lehtiö, M. Punkkinen, P. Laukkanen, K. Kokko, S. Suihkonen, H. Savin, and W. Wang, Surface Properties of p-GaN and Formation of Nickel Metal Contacts. Advanced Materials Interfaces 12 (2025) 2500163.
M. Ebrahimzadeh, S. Granroth, M. Miettinen, I. Angervo, L. Hanchen, M. Otsus, R. Punkkinen, M. Punkkinen, V. Vähänissi, K. Kokko, P. Paturi, K. Kukli, H. Savin, and P. Laukkanen: Transforming Schottky to Ohmic Contacts via Ultrahigh-Vacuum Engineered Interfacial Alloying. ACS Applied Materials & Interfaces 17 (2025) 68802.
Kuva: Hanna Oksanen / Turun yliopiston viestintä