Terahertz photonics

Abstract:

Quantum well infrared photodetector (QWIP) structures were grown by metal organic vapour phase epitaxy (MOVPE) and molecular beam epitaxy (MBE). These n-type QWIP structures were fabricated into devices. Inter-subband and inter-band transition energies were measured using photoresponse and photoluminescence spectroscopy. The carrier dynamics of one of the structures was analyzed using temperature dependent up-conversion spectroscopy. These results were modelled with the solution of a three level system. Measurement of an n-type QWIP allows us to determine the inter-subband relaxation time of a p-type QWIP. The inter-subband relaxation time of a p-type QWIP with 3 nm wide wells was determined to be 15 ps.

Abstract:

The time-resolved photoluminescence technique of picosecond excitation correlation has been applied to self-assembled InGaAs quantum dots grown in the Stranski-Krastanow mode. The nonlinear cross-correlation signal is shown to be due to filling of the quantum dot ground state causing an increase in recombination from the first excited state with increasing carrier density. Carrier relaxation times and radiative as well as non-radiative recombination times for the ground and the first excited state of the quantum dot system are determined using a model based on state filling effect.

Abstract:

Photoluminescence up conversion study of the intermixed InGaAs/GaAs and InGaAs/AlGaAs quantum wells showed that the capture of photo-excited carriers into the intermixed quantum wells is faster (25 ps) than capture into the non-intermixed quantum wells (45 ps). The reasons for this significant reduction in the capture time is related to modification of the shape of the intermixed quantum wells.