Objective
The delta-function-like density of states in self-organized QDs makes them very attractive for use as active media in semiconductor microcavities to study a number of fundamental effects and to develop a new generation of light emitting devices. Several fundamental effects will be studied experimentally and theoretically in the frame of this project; the enhancement of the spontaneous emission rate (the Purcell effect); the coupling between photonic modes and QD exciton states, the photoluminescence from a single QD in a microcavity and the polarization splitting of the optical gain band due to light scattering on a QD array. On the basis of the knowledge gained, vertical cavity surface emitting lasers and single-mode light emitting diodes, with the active media based on QDs, are to be designed, fabricated and studied experimentally and theoretically.
Description of the research activities. To fulfil these tasks QDs with very high localization energy will be grown by molecular beam epitaxy and metal organic chemical vapour deposition, and the growth parameters will be optimised to achieve a narrow QD size distribution and high photoluminescence efficiency. Microcavity structures with active media based on such QDs will be grown. These structures will be further processed for studies under optical pumping as well as under current injection. Detailed optical studies, including angle-resolved photoluminescence, optical transmission, reflection as well as investigations of their polarization dependencies will be carried out. In the case of injection structures light-current characteristics, polarization properties of spontaneous emission and lasing, relaxation oscillation will be studied. Characteristics of VCSELs, including gain, losses, and threshold current will be calculated and compared with experimental data.
Different designs of 2D and 3D semiconductor microcavities, including coupled cavities, will be theoretically simulated, and cavity modes structure will be calculated. Electron beam lithography and dry etching will be used to fabricate the microcavities and microcavity arrays that are designed. The spontaneous emission rate enhancement will be investigated by temperature and excitation - dependent time-resolved photoluminescence. Photoluminescence from a single QD will be studied by micro-photoluminescence. The polarization properties of photoluminescence, optical reflection and transmission will be studied and compared with the results of theoretical calculations. On the basis of the knowledge achieved, the design of a single mode light emitting diode will be developed. Such single mode light emitting diodes will be fabricated and their characteristics will be studied.
Expected results. Fabrication of QDs possessing very high localization energy with respect to matrix states (>400meV), narrow PL line width (<30meV), high PL efficiency (>60%), and low temperature sensitivity of the integrated PL intensity. Observation of a dramatic enhancement of the spontaneous emission rate (>100 times). Unambiguous PL from a single QDs and studies of its emission properties. Observation of the strong coupling regime of self-organized QDs in a microcavity and achievement of lasing in the strong coupling regime. Understanding of the influence of the additional light scattering on QDs in a microcavity on polarization of emission. Fabrication of vertical cavity emitting lasers with characteristics superior to those of quantum well-based devices. Fabrication of a single mode light emitting diode based on a 3D microcavity containing self organized QDs. Development of theoretical models describing semiconductor microcavities with QDs, and carrier injection in vertical cavity surface emitting lasers based on QDs.
To conclude, fundamental knowledge on the interaction between zero-dimensional excitons in QDs and low-dimensional photon modes in one-, two, and three-dimensional semiconductor microcavities will be achieved by this project and advanced microcavity enhanced devices will be fabricated and studied.
Call for proposal
Data not availableFunding Scheme
Data not availableCoordinator
10623 Berlin
Germany