MPE-lab

Physics of nanoscale devices

Nanophotonics with quantum dots

Self-assembled quantum dots (QDs) are small semiconductor particles incorporated into a host semiconductor crystal. By their small dimensions (typically 10 nm), QDs behave as artificial atoms with tunable electrical and optical properties depending on materials and size. QDs can effectively convert IR radiation to electrical current in detector applications. In a research project conducted in collaboration with Acreo and Linköping University we study novel types of effective IR detectors based on dots-in-well structures. The primary goal is to create detectors with lower dark current to minimize the requirements of expensive cooling and to enhance the responsivity. Furthermore, it is highly desirable to be able to electrically tune the responsivity peak. Together with Acreo and Linköping University we have successfully developed detectors based on InAs QDs incorporated into GaAs/InGaAs quantum well structures with good responsivity and with promising tunability within the long-wavelength IR (LWIR) and mid-wavelength IR (MWIR) regions.

Extended abstract for "Nanophotonics with quantum dots" (pdf, 95 kB)

Nanophotonics with nanowires

Semiconductor nanowires (NWs) are nanoscaled needle-shaped structures fabricated in a catalytic process starting from seed particles deposited on a substrate. NWs form the basis of completely new families of 1D electronics e.g. wrap-gate transistors, resonant tunnelling diodes, light-emitting diodes and photodetectors. Typical dimensions of the NWs are a diameter of 10-100nm and a length of several microns.. Previously we have designed and characterized IR detectors based on single InAs/InAsP NWs. We are now engaged in a project together with nmC@LU and Harvard (prof. Federico Capasso) to realize IR detectors based on large ensembles of NW detectors. The expected advantages are cheap InGaAs NW detectors grown directly on silicon, high responsivity and reduced dark current. Furthermore, the current is partitioned due to the ensemble of NWs which will reduce the risk of burned-out devices due to electric shock.

Extended abstract for "Nanophotonics with nanowires" (pdf, 130 kB)

Nanospintronics

Spintronics deals with realization of devices where the spin degree-of-freedom is used to control the electric current. The GMR effect is used already today in e.g. read/write heads in hard disks and in magnetic random access memories (MRAMs). The research in spintronics at MPE-lab is run together with the nmC@LU. Very interesting tunnelling magnetoresistance effects were recently discovered in tunnel contacts consisting of a single magnetic layer. We have also recently started a collaboration with IBM/Stanford (Dr. Stuart Parkin) to study magnetoresistance effects in NWs with ferromagnetic contacts. The ultimate goal is to realize a spin-transistor. Together with IBM, we are also presently investigating NWs as templates for extremely smooth and thin magnetic layers for storing information in magnetic domains (Race-Track memory) with expected unprecedented access time and very high reliability. We also collaborate with the group of prof. Carsten Ronning at Jena University on magneto- electrical properties of Mn+ ion-implanted semiconductor NWs. The research project is interesting both from a fundamental point of view of understanding diluted magnetism in nanostructures and for applications e.g. spin-valves and spin-LEDs fully compatible with semiconductor technology.

Extended abstract for "Nanospintronics" (pdf, 150 kB)

Nanotribology

In the ongoing project we investigate, in collaboration with the nmC@LU, the static and dynamic friction between different semiconductor surfaces and NWs being pushed across the surface with the tip of an AFM. In particular, we have investigated the dependence of the friction on surface roughness and found very interesting results. We have developed a completely new experimental technique where the friction parameters are calculated from the geometric shape of a bent wire kept in equilibrium between the internal elastic force and the friction force to the substrate.

Extended abstract for "Nanotribology" (pdf, 240 kB)

High-frequency electronics/nanosensors

This project deals with a radically new type of low-power radio-frequency transceivers for RFID and sensor network applications. For the sensor networks, we intend to combine the transceiver with sensors materials composed of e.g. carbon nanotubes/semiconductor nanowires for wireless surveillance sensor networks for medical and environmental monitoring.

Extended abstract for "High-frequency electronics/nanosensors" (EGON) (pdf, 190 kB)