P. C. Findlay

Auger recombination dynamics of InxGa1-xSb

The alloy In1-xGaxSb has been identified as potentially an important component in mid-infrared laser diodes which use band structure engineering of quantum structures based on the narrow-gap III-V material InSb. A pump-probe measurement has been made of carrier recombination in bulk In1-xGaxSb, for a range of alloy compositions. Over the range of excited carrier densities (5 × 1016-3 × 1017 cm-3) and at the temperatures (30-300 K) studied experimentally, contributions to the recombination from Auger, Shockley-Read-Hall and radiative mechanisms were calculated using an analytic approximation, with carrier degeneracy included. Excellent agreement with experiment was obtained over the alloy range x = 0.0-0.2 (corresponding to a room-temperature energy gap variation from 0.175 eV to 0.215 eV). Numerically the room-temperature Auger coefficient, C, decreased from the value 1.17 × 1026 cm6 s-1 at x = 0 (i.e. InSb) to 0.98 × 1026 cm6 s-1 at x = 0.2. The fact that C decreases with energy gap increase, in good agreement with theoretical predictions, is important for strained layer quantum well device applications.

Auger recombination dynamics of lead salts under ps free electron laser excitation

Pump-probe transmission experiments have been performed on PbSe above the fundamental absorption edge near 4 μm in the temperature range 30 to 300 K, using the Dutch ps free-electron laser. For temperatures below 200 K and carrier densities above the threshold for stimulated emission, stimulated recombination represents the most efficient recombination mechanism with relatively fast kinetics in the 50–100-ps regime, in good agreement with earlier reports of photoluminescent emission. Above this temperature Auger recombination dominates, and the Auger coefficient C is determined from the pump-probe decay curves. In the low-temperature regime the Auger coefficient is determined from the decay curves at times beyond 100 ps. The Auger coefficient is approximately constant (with a value of about 8×10 -28  cm 6 s -1 ) between 300 and 70 K, and then drops a value of about 1×10 -28  cm 6 s -1 at 30 K, in good agreement with the theory for nonparabolic near-mirror bands and nondegenerate statistics. It is found that C for PbSe is between one and two orders of magnitude lower than for Hg 1-x Cd x Te of comparable band gap.

Bound-bound intraband resonance and inhomogeneous photoluminescence broadening in InAs/GaAs quantum dots

We have developed an inter-/intra-band double-resonance technique that has allowed us to make an unequivocal assignment of the resonant bound-bound intersublevel absorption in self-organized InAs/GaAs quantum dots. We have applied the technique to dots grown at a low growth-rate, which show well resolved photoluminescence (PL) lines. The double resonance (far infrared modulated photoluminescence, FIR-MPL) and its polarisation selection rules allows us to identify not only the levels involved in the PL transition but the relative importance of the causes of its inhomogeneous broadening. The PL and the FIR-MPL were collected simultaneously to ensure the correspondence of features in each by monitoring both the DC and AC outputs of the detector. Spectra were obtained by scanning either the monochrometer at fixed FIR frequency or scanning FELIX at a fixed PL frequency. The results unequivocally confirm that the interband PL lines arise from successively increasing in-plane quantum numbers, with the lowest electronic states separated by 55 meV and corresponding hole states by 13 meV. Most importantly we believe that our method can distinguish between the three PL inhomogeneous broadening mechanisms expected to be significant in our self-assembled system of dots (a) in-plane dot size variation, (b) out-of-plane or potential broadening, and (c) compositional broadening associated with fluctuations of In within the dot.

Optically detected intersublevel resonance in InAs/GaAs self-assembled quantum dots

Abstract We present two-colour pump–probe measurements of the intraband absorption in low growth rate, self-assembled InAs/GaAs quantum dots. The far-infrared resonance observed is unambiguously associated with the dots, and not related to the surrounding material. The results also imply that the interband photoluminescence lines, which appear under high excitation, are from conduction band levels with successively increasing in-plane quantum number.