Electrical characteristics of semiconductor diodes: measurement and modelling.

(supervisor: Andrew Evans)

Nature of project: experimental, data analysis

Available to full-time physicists 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. This project involves the measurement of I-V characteristics for commercial diodes and device structures fabricated in-house. These characteristics can then be modelled using a suitable theoretical description of the electronic transport mechanisms. For metal-semiconductor contacts, the interface potential barrier can be very sensitive to the metal used and also to the semiconductor processing steps. I-V characteristics can be used to determine the value of the potential barrier for a given contact. The project will involve the fabrication of metal contacts on compound (III-V) and elemental (silicon, diamond) semiconductors to produce both low-resistance (ohmic) and rectifying (Schottky) junctions.

A successful project will develop beyond the above in one/some of the following directions:
Development of the project would be a focus on p-type diamond as an electronic material for extreme environments such as high temperature, corrosive environments and space applications. The project could also be extended to include other characterisation methods for example to investigate the chemical or optical properties of the device.

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.

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