Interband light absorption in semiconductor quantum dots

in a magnetic field connected with exciton - donor complexes

A.P.Djotyan, A.A.Avetisyan, E.M.Kazaryan and K.Moulopoulos*

Yerevan State University, 1 A.Manoogian, 375025,Yerevan, Armenia. E-mail:

*University of Cyprus, Department of Physics, P.O.Box 20537,1678, Nicosia, Cyprus

The investigation of optical properties of three dimensionally confined electrons and holes in semiconductor quantum dots (QDs) in external fields are very important because of their potential applicability to novel quantum devices. The excitons bound to charged or neutral impurities and trions play an important role in absorption and photoluminescence spectra of QDs [1]. In QD due to strong overlapping between the wave functions of the electrons and holes the complexes of quasiparticles such as biexcitons, trions or impurity bound excitons become more stable in comparison with bulk semiconductor. In [2] we have investigated the energy of the ground state of charged exciton-donorcomplex (EDC), which consists of an exciton bound to a positive singly charged donor, in a semiconductor QD in the presence of a magnetic field. The theoretical analysis was carried out using a variational approach in the adiabatic approximation ( and are the effective masses of electron and hole).



Rashba and Gurgenishvili (1962) predicted that an exciton bound to impurity in bulk semiconductor has giant oscillator strength that is many orders of magnitude larger than the oscillator strength of a free exciton. The oscillator strength for the interband absorption in a QD connected with the EDC is investigated in [1]. In this work we have investigated the oscillator strength behavior for the optical transition from valence band to the ground state of charged EDC in a spherical QD in the presence of a magnetic field. In Fig.1 we present the obtained dependences for the oscillator strength of the charged EDC (with) on magnetic field dimensionless parameter (with the cyclotron frequency ) in the case of infinite barrier of the QD for different values of the QD radius d. As is it shown on Fig.1, oscillator strength (in per units of the QD volume) with the increase of magnetic field drastically increases for small values of QD radius d (curve 3), while in the case of larger QD radiithe dependence is a slow function of magnetic field (curves 1, 2). These results are in accordance with behavior of the binding energy of EDC in the QD in the magnetic field [2].


This work is supported byArmenian State Program“Semiconductor Nanoelectronics”.

[1] A.A.Avetisyan, A.P.Djotyan and E.M.Kazaryan. J.Key Engineerin Materials, v. 277-279, 893 (2005).

[2] A AAvetisyan, A.P.Djotyan, E.M.Kazaryan and K.Moulopoulos, Phys.Stat.Sol.(c) v.3, No. 4,

1087 (2006).