Module 2: Inorganic semiconductor nanostructures (PHY6002)
The physics and technology of semiconductor nanostructures - status and trends.
Above: AFM image of a quantum dot.
Semiconductor I.C. feature sizes have decreased dramatically in recent years. The Pentium 4 processor was based on 130 nm size features, and the present rate of decrease will soon require the large-scale utilisation of true nanostructure devices.
Lasers based on nanosized semiconductor objects (quantum dots) have been fabricated in research labs, as have transistors operating with a single electron. This module will look at the physics and technology of semiconductor nanostructures, considering both the present status and possible future trends.
Outline syllabus
- Overview/revision of semiconductor physics
- Fabrication techniques
- Electronic structure and physical processes in semiconductor nanostructures
- Principles and performance of semiconductor nanostructure-based electronic and electro-optical devices
- Future developments and trends
Semiconductor quantum dots
Zero-dimensional dots are formed during the epitaxial growth of two semiconductors (InAs and GaAs) with different inter-atomic spacings.
The dots have spatial dimensions of a few nanometers (as seen in the image above left).
Possible applications include lasers, optical memories, far infra-red photon detectors and sources for single photons.
Quantum dot lasers
Above: Band structure of a quantum cascade laser.
Lasers based on quantum dots are predicted to exhibit lower operating currents, reduced sensitivity to temperature changes and faster operating speeds in comparison to conventional lasers. Some of these advantages have now been demonstrated experimentally. The figure shows spectra from a quantum dot laser for different drive currents.
Quantum cascade lasers
Utilising optical transitions between electronic states in ultra-thin semiconductor layers, the quantum cascade laser produces coherent far-infrared light. Applications include gas sensing, short-range free-space communications, medical analysis and military detector blinding.
Quantum dot optical memory
Quantum dots are used to store electrons created by incident photons. The stored electrons alter the electrical resistance of the device, forming the basis for a high density memory structure. Further work is aimed towards an all-optical memory which can be both written to and read from using photons.
Above right: Schematic of the band structure of a quantum dot optical memory.
Back to: Nanoelectronics and nanomechanics
