Physics projects for Y3 and Y4 students

Project description

Electrical characteristics of wide band-gap semiconductor diodes

(supervisor: Andrew Evans)

Nature of project: experimental, data analysis

Available to students on full-time physics degree schemes only.

Project description and methodology

Solid state electronic and optoelectronic devices such as transistors, LEDs and photovoltaic cells that are based on semiconducting materials rely on interfaces between different materials for their operation. These include p-n junctions, semiconductor heterojunctions and metal-semiconductor (M-S) contacts. The device operation requires a knowledge of the fundamental properties of these junctions, in particular the relationship between the applied voltage (bias, V) and the current (I) for such non-linear devices. Such semiconductor diodes are the most efficient detectors and emitters of light from the infrared to ultraviolet and are also used for detecting higher energy radiation such as x-rays. This project involves the fabrication and measurement of diodes based on wide band-gap semiconductors for the detection of low wavelength visible light and x-rays. For metal-semiconductor contacts, the interface potential barrier can be very sensitive to the metal used and also to the semiconductor processing step. The measured I-V characteristics will be modelled using a suitable theoretical description of the electronic transport mechanisms and to determine the value of key parameters such as the potential barrier.

A successful project will develop beyond the above in one/some of the following directions:
Development of the project would involve the characterisation of diodes under different operating conditions e.g. in air, vacuum and at high temperature. It could also involve the automation of the measurement process and advanced modelling.

When considering where to take your project, please bear in mind the time available. It is preferable to do fewer things well than to try many and not get conclusive results on any of them. However, sometimes it is useful to have a couple of strands of investigation in parallel to work on in case delays occur.

Additional scope or challenge if taken as a Year-4 project: As a 4th year project, the fabrication and characterisation would be combined in an in-situ system that would require design and construction of vacuum and electrical equipment to enable the parallel characterisation of the chemical and optical properties of the device. The project will assess the practicality of devices based on SiC and diamond as high energy radiation detectors for space applications.

Please speak to Andrew Evans (dne) if you consider doing this project.

Initial literature for students:

  1. Physics of semiconductor devices, S. M. Sze (Primo)
  2. Semiconductor devices : basic principles, Jasprit Singh (Primo)
  3. Semiconductors and electronic devices, Adir Bar-Lev (Primo)

Novelty, degree of difficulty and amount of assistance required

The measurement requires some modification to existing equipment and the modelling requires some knowledge of numerical computational methods. The use of research-grade equipment increases the difficulty and novelty level of the project.

Project milestones and deliverables (including timescale)

milestoneto be completed by
Review of materials and methodend of October
Decision on semiconductor deviceChristmas
First measurements on standard diodesend of February
Fabrication and measurement of device structuresEaster

Students taking this project will have to submit a full risk assessment form