Skip to main content
European Commission logo print header
Content archived on 2022-12-23

Optically and electrically controlled Flash memory device based on self-organized quantum dot structures

Objective

It is proposed to develop a new type of nonvolatile Flash memory device based on self-organized quantum dots (QDs) as optically- and electrically-controlled traps for charge carriers. Optical programming of the Flash memory device will be based on exploitation of the spectral hole burning (SHB) effect. The using of this new physical concept for a Flash memory device has the advantages of higher density and faster programming rate compared to the existing tunnelling and hot-carrier Flash memories.
A plane of self-organized QDs in a wider band gap matrix is characterised by efficient photoluminescence (PL) due to the recombination of confined electron and holes. The PL line has large inhomogeneous broadening, linewidth GammaI ~ 100µeV, due to variations in the size of the QDs. However, a single QD has an ultra-narrow homogeneous broadening with Gammah < 100µeV due to the discrete, atomic-like energy levels of a QD. Such a system, where GammaI >> Gammah, offers the possibility of SHB, which has the potential to form a multiple-wavelength, optical memory device. SHB occurs when an inhomogeneously broadened absorption line is locally modified in frequency space. This will be achieved by producing a photo-induced change in the charge state of the QDs with transition energies within the frequency line width of a tunable laser. The presence, or absence, of a spectral hole at a given wavelength could then be used to represent binary data. The multiplexing factor (MPF), which is the ratio of the inhomogeneous line width (GammaI) to the homogeneous line width (Gammah), can be quite large; as many as a thousand or more bits of data can be stored in a volume irradiated by a single, focused laser beam.
Persistent spectral hole burning (PSHB) requires the presence of a single carrier in the QDs contributing to the spectral hole. It is necessary, therefore, to remove one of the photoexcited carrier species from the system. This will be achieved electrically by embedding the QDs in a suitable semiconductor heterostructure matrix. The use of semiconductor matrices allows us to separate one species of the photogenerated carriers by the application of an external electric field in specially designed heterostructures with barriers. This provides an alternative electro-optical method of producing a spectral hole. In addition, since the photocurrent through this structure reflects the absorption spectrum, this allows us to combine hole burning with detection in a single device. The use of a semiconductor material as a matrix for QDs permits the detection of spectral holes under optical excitation using photocurrent devices. The optical programming of the devices will be achieved by using a set of laser diodes based on the same type of QDs.
It is planned to investigate carrier transport (such as capture and emission of carriers, storage and transfer of charge) in semiconductor structures with self-organized QDs. By using both p- and n-type doped matrices it is possible to study electron and hole states in QDs separately. Investigations of the influence of the electric field and the electron-phonon interaction on the emission rate of carriers from the QDs will be carried out. This is essential for the proposed room temperature operation. The influence of charge located in the plane of QDs on the distribution of the electric field through the structure will also be studied. The principal effort will be concentrated on the deepening of electron and hole states in QDs with respect to the host matrix. This will rely on two basic ideas: firstly, by changing of the matrix band gap and secondly, through a controllable change of the size, shape and composition of the QDs. Then it is planned to design the tunnel barrier heterostructures for separation of photo-induced carriers in the QDs.
The ultimate goal is to use the measured data on the properties of self-organized QDs in a semiconductor matrix to design an optical memory device, which operates at room temperature. This could be of considerable importance technologically, for in the development of optical computers. The work will be carried out by teams within a strong, existing collaboration.

Call for proposal

Data not available

Funding Scheme

Data not available

Coordinator

University of Nottingham
EU contribution
No data
Address
Unversity Park
NG7 2RD Nottingham
United Kingdom

See on map

Total cost
No data

Participants (3)