Time-resolved four-wave mixing in InAs/InGaAs quantum-dot amplifiers under electrical injection

• Published in: Applied physics letters Vol. 76; no. 11; pp. 1380 - 1382
• Main Authors: Borri, P., Langbein, W., Hvam, J. M., Heinrichsdorff, F., Mao, M.-H., Bimberg, D.
• Format: Journal Article
• Language: English
• Published: 13-03-2000
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.126038

Time-resolved four-wave mixing in an InAs/InGaAs/GaAs electrically pumped quantum-dot amplifier is measured at room temperature for different applied bias currents going from optical absorption to gain of the device. The four-wave mixing signal from 140 fs pulses shows a transition from a delayed photon-echo response in the absorption regime to a prompt free polarization decay in the gain regime. This corresponds to a pronounced reduction of the dephasing time from 250 fs at zero bias to less than 50 fs at the maximum applied current. The four-wave mixing response at transparency of the device shows a composite structure with both photon echo and free-polarization decay. This is a signature of the digital occupation number in quantum dots, resulting at transparency in a signal from dots occupied with either zero or two excitons corresponding to absorption or gain of the dot ground state.