Summary of Research Project Results under JSPS FY2001
"Research for the Future Program"

1.Research Institution University of Tsukuba
2.Research Area Physical and Engineering Sciences
3.Research Field Exploratory Research on Novel Artificial Materials and Substances for Next-Generation Industries
4.Term of Project FY 1997 〜 FY 2001
5.Project Number 97P00106
6.Title of Project Quantum Nonlinear Effects in Nanostructures and their Applications

7.Project Leader
Name Institution,Department Title of Position
Mitsuo Kawabe University of Tsukuba, Institute of Applied Physics Professor

8.Core Members

Names Institution,Department Title of Position
Yasuaki Masumoto University of Tsukuba, Institute of Physics Professor
Hiroki Nakatsuka University of Tsukuba, Institute of Applied Physics Professor
Toshiaki Hattori University of Tsukuba, Institute of Applied Physics Associate Professor

9.Summary of Research Results

 In quantum dots, resonant energies of quantum levels change their energies with the change of their sizes, the linewidths of the quantum levels are very sharp and confined electrons and holes mutually interact strongly. All of these features of the quantum dots are of benefit to sensitive optical switches operating under the weakest light. For the basic study of QDs, we have extensively studied the optical response of quantum dots by investigating the electronic states and dynamics of the excited states in quantum dots, and then have given bases to the application of the quantum dots to optical switch and optical memory. Clarifying the homogeneous optical spectra of quantum dots and its responsible physical mechanism are also extensively studied because the homogeneous width is closely connected with the optical nonlinearity. Extension of the wavelength tunability of the ultrafast optical switch of quantum dots to the infrared region and exploring the new optical functionality of quantum dots have been studied for application of QDs.
 Enhancement and control of nonlinear optical effects of quantum nanostructure materials were achieved using photonic crystal structures. By doping nonlinear optical materials such as semiconductor dots in a defect layer of one-dimensional photonic crystals, drastic enhancement of the effective nonlinearity was achieved. Theoretical analysis for the optimization of the device parameters was performed and the prediction was verified by experiments. Ultrafast response of the photonic crystal nonlinear devices doped with semiconductor and metal quantum dots was observed by femtosecond pump-probe measurements.
 In order to take the advantage of these properties for device application we should improve the dot size homogeneity and increase the dot density. The conventional method for dot formation is the self-assembling growth, while the fundamental growth mechanism is not clear, In this project we investigated the growth mechanism of self-assembled quantum dots for improvement of dot-size homogeneity, high density and ordering of dot array. We have successfully demonstrated 20 layer stacking of InAs QD layers without deterioration of QD size and homogeneity by using strain compensation and suppression of segregation structures.

10.Key Words

(1)quantum dot、(2)optical switch、(3)optical memory
(4)homogeneous width、(5)nonlinear optics、(6)photonic crystal
(7)femtosecond、(8)strain compensation、(9)high density quantum dot、(10)quantum dot superlattice