Explore the up-limitation of defect density in III-V semiconductor for achieving silicon photonic

There is an increasing demand of developing III-nitride based laser diodes with a long wavelength recently, which is expected to play a key role in displays, visible light communications, etc. Generally speaking, III-nitride laser diodes will have to be grown on native substrates, i.e., GaN substrates. Unfortunately, GaN substrates with a reasonably large size are very expensive. Therefore, it is necessary to develop a new technology for the growth of III-nitride based laser diodes on foreign substrates, such as silicon. In that case, a number of fundamental challenges needs to be overcome, where it is a first priority to understand fundamental physics, such as the up-limitation of the dislocation density in III-nitrides on silicon beyond which lasing cannot be achieved.   

Homo-epitaxial growth is ideal and has been widely used in the growth of III-V semiconductors except III-nitrides and as a result the last 3-4 decades have seen huge successes in III-V semiconductors, especially for GaAs. The research activity on “lattice mismatched hetero-epitaxy” for III-V semiconductors started a long time ago, early GaP grown on Si and GaAs on Si, now III-nitrides on Si. Lattice mismatched hetero-epitaxy normally generates a high density of defects in III-V semiconductors. For example, the dislocation density of GaN on silicon is typically 109-1010/cm2, while the dislocation density of GaAs on silicon is more than 106/cm2 even if so-called dislocation filtering technologies are used. Such figures are at least two or three orders of magnitude higher than those of their counterparts via homoepitaxy. However, the last two decades have seen a great success in lattice mismatched hetero-epitaxy, represented by GaAs on silicon and GaN-on-sapphire. By looking into the great success in achieving GaN optoelectronics and other III-V optoelectronics on silicon, there is a common feature, i.e., the enhanced performance can be achieved only through epitaxially growing a three-dimensionalconfinement structure as an active region, meaning either a quantum dot (QD) structure or a QD-like structure as an active region. Therefore, it is necessary to understand the fundamental physics behind that, and then to explore the up-limitation in terms of defect density, beyond which III-V semiconductors with reasonably good device performance cannot be achieved even if QD structures as an active region are utilised.   

The project starts with simulation and modelling work, followed by carrying out the epitaxial growth of III-nitride laser structures by means of advanced MOVPE technique and then device fabrication.  

How to apply:

Applicants should apply to the Doctor of Philosophy in Physics and Astronomy with a start date of 1st October 2025. 

Applicants should submit an application for postgraduate study via the Cardiff University webpages (https://www.cardiff.ac.uk/study/postgraduate/research/programmes/programme/physics-and-astronomy) including: 

• your academic CV (Guidance on CVs for a PhD position can be found on the FindAPhD website)

• your degree certificates and transcripts to date including certified translations if these are not in English 

• a personal statement/covering letter 

Ensure your personal statement (as part of the university application form, or as a separate attachment, if you prefer) provides a clear explanation of your research interest, preparation undertaken, and an understanding of the project. 

Your personal statement should be no more than 500 words, and address the following questions:

1. What are your scientific research interests and ambition?

2. How has your academic and/or professional journey prepared you for PhD study? (for instance, give examples of work you particularly enjoyed, of challenges you overcame, of connecting with others about your work or ideas, of showing inventiveness, of developing new skills and knowledge)

3. Why do you think this project is important?”

• two references (applicants are recommended to have a third academic referee, if the two academic referees are within the same department/school). Your references can be emailed by the referee to [email protected]  

Please note: We are do not contact referees directly for references for each applicant due to the volume of applications we receive.     

Candidates should hold or expect to gain a first-class degree or a good 2.1 (or their equivalent) in Engineering, Physics or a related subject. Desirable skills are knowledge of Quantum Physics, Optics, Semiconductors, Technology, Physics, Engineering.

Applicants whose first language is not English are normally expected to meet the minimum University requirements (e.g. IELTS 6.5 Overall with 5.5 minimum in sub-scores) (https://www.cardiff.ac.uk/study/international/english-language-requirements) 

In the “Research Proposal” section of your application, please specify the project title and supervisors of this project and copy the project description in the text box provided.

In the funding section, please select that you will not be self-funding and write that the source of funding will be EPSRC. 

Once the deadline for applications has passed, we will review your application and advise you within a few weeks if you have been shortlisted for an interview. 

Eligibility :

This studentships are available to home and international students. International students will not be charged the fee difference between the UK and international rate. Applicants should satisfy the UKRI eligibility requirements.

For more information, or if there are any questions re application process, please contact Physics and Astronomy PGR Student Support team at [email protected]