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Advanced Semiconductor Device Materials

III-Nitrides for next generation rf and power electronics

The physical properties of the III-Nsemiconductors make them ideal for reducing energy consumption, improving performance and reducing costs in high power and high frequency electronic systems. However, substantial development of both material and devices is needed to fully exploit the advantages of the III-N technology and to make it commercially viable.We have identified several scientific and technological challenges which must be addressed to exploit the full potential of III-Nitrides with applications in the next generation of wireless communication, sensing, and power infrastructures. The research is in the heart of a the newly established competence center C3NiT-Janzén, which has the mission to perform and transfer research results on III-Nitride high frequency and high power technology directly exploitable by industrial partners at different levels in the supply-chain. More specifically my research includes optimization of epitaxial design of GaN and AlGaN device structures on SiC, GaN and AlN substrates for microwave and power electronics.  This activity covers the actual growth of the device structures with the main aim to minimize defect densities (dislocations and background impurities), and the design of the epi-stack targeting different functionalities, e.g. power amplification, noise, and flicker-noise, switch losses, device design, etc. Further research activities include studying, understanding and optimizing n- and p-type doping in Al,In(Ga)N epitaxial layers and 2DEG in heterostructures by employing unique THz spectroscopic ellipsometry and optical Hall effect methods at the THz Materials Analysis Center.

Research financed by VR, VINNOVA and SSF

Cooperation with SweGaN, Saab, ABB, Ericsson, On Semiconductor, Ericsson, Gotmic, UMS, Epiluvac, FMV, Chalmers University and Lund UNiversity

Gallium Oxide and related materials

The aim is to develop of a new wide band gap semiconductor material – β-Ga2O3 for applications in high-power electronic devices with substantial efficiency gain in e.g., generation and transmission of electric power, electrification of vehicles and motor drivers. β-Ga2O3 has superior material properties such as higher band gap and break-down voltage, combined with significantly lower substrate price compared to widely studied wide band gap materials such as SiC and GaN. Initially we will primarily focus on the development of metalorganic vapor phase epitaxy of β-Ga2O3 exploring growth conditions and different precursors. This activity also includes modification of an existing growth reactor and modeling of temperature and gas flow profiles in order to optimize reactor design and growth.  In parallel I will also investigate the free-charge carrier properties of β-Ga2O3 substrates and device structures grown by molecular beam epitaxy from Tamura Co. and Tokyo University. The knowledge gained in these initial studies will be used to optimize doping in our MOVPE β-Ga2O3 during later stage of developments. In this period the free-charge carrier properties will be studied as a function of doping and surface orientations. First test device structures will be designed and grown.Vertical and horizontal power devices will be fabricated and characterized in collaboration with Chalmers University.

Research financed by Swedish Energy Agency and VR

Cooperation with SweGaN, Epiluvac and Chalmers University

Graphene and 2D electronic materials

Contemporary CMOS technology is stretched to its scaling limits and new materials with superior transport properties are pursued to fuel the increasing demands of high-speed electronics. To address these issues we explore the potential of epitaxial graphene grown on SiC and 2D electronic systems such 2DEG in AlInN/GaN and AlGaN/GaN. We study the electronic, transport and structural properties of graphene and 2D electronic systems and provide feedback to the growth. We explore different substrate polytypes, surface orientations, surface treatments and modifications to establish the mechanisms that control doping and electronic properties in graphene and AlIn(Ga)N/GaN. The research aims at enabling the desired transport and electronic properties in these materials in order to achieve substantial advance towards high-speed and THz-frequency large scale processor technologies.

Research financed by SSF, VR and VINNOVA

Cooperation with Graphensic AB

InN and related alloys

InN is a narrow band gap (0.6 eV) semiconductor, holding a great potential, when alloyed with GaN (3.4 eV) and AlN (6.0 eV), for highly efficient solar cells, a variety of optoelectronic devices operating from the near-IR to deep UV, THz emitters, high-frequency transistors and sensors. Strong variation of carrier concentration across the thickness of InN layers is observed. The underlying doping mechanisms are highly debated and the mechanisms to control free-charge carrier properties are not yet identified, which precludes the application of InN-based materials. Our major goal is to study and understand the physical mechanisms responsible for the bulk and surface doping and surface charge behavior of InN and related alloys. In particular, we study the effect of surface orientation, crystal modification, defects and doping on the surface charge accumulation and bulk doping in epitaxial InN and InGa(Al)N films. We also study alloying effects on phonons, elastic properties, piezoelectric polarization and strain in InAlN films and nanostructures.

Research financed by VR and FCT, Portugal

Cooperation with Ritsumeikan University, Chiba University, University of Montpellier and Theoretical Physics at LiU.

Novel nitride alloys and nanostructures

Alloying group III A and III B nitrides offers a pathway to create new functionalities and engineer the optical and electronic properties of nitrides. Recently, ScAl(Ga)N and YAl(Ga,In)N have received significant interest due to their attractive optoelectronic and piezoelectric properties, and their compatibility with GaN technology. However, very little is known about these materials and their potential in future photonic and electronic devices needs to be established. To address these demands we study the optical properties, dielectric functions and phonons in YAlN, ScAlN and related nanostructures.

Research financed by Linköping University and FCT, Portugal

Cooperation with Thin Film Physics and University of Nebraska-Lincoln

THz ellipsometry and Optical Hall effect

We aim at developing unique THz ellipsometry and magneto-ellipsometry (THz Optical Hall effect) methodologies. These novel techniques will make it possible to explore electronic, transport and magnetic properties and phenomena in e.g, semiconductors, nanomaterials, organic materials, which cannot be assessed by other means. In short term perspective we expect to develop understanding and create knowledge about the mechanisms that control the free-charge carrier properties of epitaxial graphene and III-nitride heterostructures in order to achieve their desired transport properties. As a result of our research we will foster progress in novel technologies and functionalities based on epitaxial graphene and III-nitrides, such as THz electronics, power electronics, highly efficient solid state lighting and photovoltaics. Our ambition is to establish a unique center for THz and magneto-optic ellipsometry at Linköping.

Research financed by SSF, ÅForsk and VINNOVA

Cooperation with J. A. Woollam Co and CMO at University of Nebraska-Lincoln

Vanya Darakchieva
Associate Professor (Docent)

Senior Lecturer,
Head of Unit

Advanced Semiconductor Device Materials


E-mail: vanya@ifm.liu.se
Phone: +46 (0)13 28 57 07

Room M323 (Physics Building)

Semiconductor Materials, IFM
Linköping University
Linköping, Sweden


Responsible for this page: Vanya Darakchieva
Last updated: 03/11/18