Intraband polaron dynamics of excited carriers in $\mathrm{InAs}∕{\mathrm{In}}_x{\mathrm{Al}}_{1-x}\mathrm{As}$ quantum dots

The lifetime of excited carriers in $\mathrm{InAs}∕\mathrm{InAlAs}$-on-InP quantum dots is investigated using intraband photoconductive (PC) spectra. A method is presented, based on the analysis of temperature dependence and line shape of PC signals, by which the dynamic properties are derived. Detailed analysis of PC measurements is a powerful method of studying the recombination dynamics. Temperature and energy dependencies are governed by strong electron-phonon interaction. The drop in PC signal with temperature is attributed to increased polaron relaxation due to the increased LA phonon population. Recombination at large detuning from LO phonon energy, as opposed to phonon bottleneck, renders an asymmetric line shape. The peak PC signal is redshifted due to an increased lifetime with detuning.

Figure 1

PC signal vs excitation energy at 15–50 K for wedge illumination: (a) 70–130 meV and (b) 240–350 meV. The dip at 290 meV is due to ${\mathrm{CO}}_2$ atmospheric absorption.

Figure 2

Fit of temperature dependence of integrated intensity of the 100 meV peak, based on a two-LA-phonon relaxation model.

Figure 3

Schematic diagram of the QD energy levels associated with excitation and relaxation.

Figure 4

Line shape fit for 100 meV peak for two biases. $V_B=0.75\mathrm{V}$ curve is multiplied by 8 and shifted downwards for better comparison. Concave curve shows increase of polaron lifetime with detuning.

Figure 5

Bias dependence of the 100 meV peak. Solid line shows WKB fit for tunneling.