Applications are invited for a 3-year PhD position within the field of epitaxial growth of highly efficient quantum dot (QD) gain material to the silicon platform.
The project will bring together several topics in the fields of semiconductor QD epitaxial growth, metamorphic epitaxial growth, crystallography, optical characterization, and photonic device fabrication.
The project will be carried out at the Department of Photonics Engineering, Technical University of Denmark (DTU) in collaboration with the Technical University of Berlin in Germany. An external research stay at the Technical University of Berlin will be possible.
The PhD-project is funded through the Villum foundation’s Young Investigator Programme award to Dr. Semenova.
In the last two decades significant progress has been made in silicon (Si) photonics. Si-based technology has number of advantages; most notably is the compatibility with automated production lines with high-resolution lithography. This allows for higher yield of low propagation loss waveguide components compared to III-V devices.
However, hampering the developments is the fundamental problem of fabrication of an efficient light source on the Si platform. Si is an indirect bandgap material, i.e. the crystal momentum of the electrons in the conduction band is not the same as that of the holes in the valence band. That means that the optical transition rates are low compared to nonradiative processes since phonon interactions are needed to take away the excess momentum. As a result of this silicon shows very poor quantum efficiency of light emission. Developing the technology which brings an efficient laser source to the silicon chip will revolutionize optical communication and bring the benefits of low-cost and low energy consumption components to our everyday life.
A lot of work has been done in order to force an indirect bandgap material to lase. Nevertheless, since the efficiency of the emitters cannot be neglected the large intrinsic performance advantages of III-V semiconductors compared to the Si or Si-Ge based contenders will force us to find a smart way of integrating III-V active material with the Si platform. The current way of avoiding the direct epitaxial growth of III-V on Si is wafer bonding, where an epi-structure is grown on a lattice matched wafer and afterwards bonded to Si followed by removing the original wafer or transfer printing of epitaxial layers .
Direct epitaxial growth of III-V on Si is a very challenging task due to the lattice mismatch, different number of atom types in the lattice and the difference in thermal expansion coefficients. The mentioned complications result in a high density of threading dislocations, anti-phase domains, and stacking fault formation. In order to suppress penetration of the mentioned crystal defects into the active layers, thereby providing high optical quality of the active material, the growth conditions and design of buffer transition layers should be carefully prepared. The crystalline growth of materials on a substrate which is highly mismatched with respect to the lattice parameter in a way where the epitaxial layer is completely relaxed is called metamorphic growth .
The project is dedicated to develop direct epitaxial growth of III-V semiconductors on Si, to demonstrate the transfer of the QD epitaxial growth technology developed for III-V material system to the Si platform and to demonstrate a defect-free high optical quality gain medium for device applications.
This research will mainly be carried out in the state-of-the-art national clean room facility DTU Danchip.
 Gunther Roelkens, Liu Liu, Di Liang, et al., Laser Photonics Rev. 4, No. 6, 751–779 (2010)
 E S Semenova, A E Zhukov, S S Mikhrin, et al., Nanotechnology 15 S283–S287(2004)
Candidates should have a master's degree in physics, nanotechnology, photonics engineering or a similar degree with an academic level equivalent to the master's degree in engineering. Candidates with experience in clean-room fabrication, optical characterization, semiconductor physics and photonics are encouraged to apply.
Moreover, the candidate shall have additional skills such as:
- Ability to work independently, to plan and carry out complicated tasks, and to be a part of a large, dynamical group
- Good communication skills in English, both written and spoken
- Familiarity with clean-room facilities is highly appreciated.
Approval and Enrolment
The scholarships for the PhD degree are subject to academic approval, and the candidates will be enrolled in one of the general degree programs of DTU. For information about the general requirements for enrolment and the general planning of the scholarship studies, please see the DTU PhD Guide.
You can read more about Department of Photonics Engineering on www.fotonik.dtu.dk
Assessment will be by Assistant Professor Elizaveta Semenova and Associate Professor Kresten Yvind.
Salary and appointment terms
Salary and appointment terms are consistent with the current rules for PhD degree students.
The period of employment is 3 years.
The start date is flexible, but preferably in the spring of 2014.
For further information please connect with Assistant Professor Elizaveta Semenova, phone: +45 25 63 85, email: firstname.lastname@example.org or Associate Professor Kresten Yvind, phone: +45 25 63 66, email: email@example.com
The application must be received no later than March 15 2014 by using the online system at DTU.
Applications must be submitted as one PDF file containing materials to be given consideration. Please open the link "apply for this job online“ and fill in the application form and attach the following documents:
- A letter motivating the application (cover letter)
- Curriculum vitae
- Grade transcripts and BSc/MSc diploma - Excel sheet with translation of grades to the Danish grading system (see guidelines and excel spreadsheet here)
Candidates may apply prior to obtaining their master's degree, but cannot begin before having received it.
All interested candidates irrespective of age, gender, race, disability, religion or ethnic background are encouraged to apply.
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