Energy transfer of excitons between quantum wells separated by a wide barrier
We present a microscopic theory of the excitonic Stokes and anti-Stokes energy-transfer mechanisms between two widely separated unequal quantum wells with a large energy mismatch ({Delta}) at low temperatures (T). Several important intrinsic energy-transfer mechanisms have been examined, including dipolar coupling, real and virtual photon-exchange coupling, and over-barrier ionization of the excitons via exciton-exciton Auger processes. The transfer rate is calculated as a function of T and the center-to-center distance d between the wells. The rates depend sensitively on T for plane-wave excitons. For localized excitons, the rates depend on T only through the T dependence of the exciton localization radius. For Stokes energy transfer, the dominant energy transfer occurs through a photon-exchange interaction, which enables the excitons from the higher-energy wells to decay into free electrons and holes in the lower-energy wells. The rate has a slow dependence on d, yielding reasonable agreement with recent data from GaAs/Al{sub x}Ga{sub 1-x}As quantum wells. The dipolar rate is about an order of magnitude smaller for large d (e.g., d=175Aa) with a stronger range dependence proportional to d{sup -4}. However, the latter can be comparable to the radiative rate for small d (e.g., d{<=}80Aa). For anti-Stokes transfer through exchange-type (e.g., dipolar and photon-exchange) interactions, we show that thermal activation proportional to exp(-{Delta}/k{sub B}T) is essential for the transfer, contradicting a recent nonactivated result based on the Fo''rster-Dexter's spectral-overlap theory. Phonon-assisted transfer yields a negligibly small rate. On the other hand, energy transfer through over-barrier ionization of excitons via Auger processes yields a significantly larger nonactivated rate which is independent of d. The result is compared with recent data.
- Sponsoring Organization:
- (US)
- OSTI ID:
- 40205646
- Journal Information:
- Physical Review B, Vol. 62, Issue 20; Other Information: Othernumber: PRBMDO000062000020013641000001; 129043PRB; PBD: 15 Nov 2000; ISSN 0163-1829
- Publisher:
- The American Physical Society
- Country of Publication:
- United States
- Language:
- English
Similar Records
Mechanistic Understanding and Rational Design of Quantum Dot/Mediator Interfaces for Efficient Photon Upconversion
Tunable radiationless energy transfer in Eu[Au(CN){sub 2}]{sub 3} {center_dot} 3H{sub 2}O by high pressure