Nonradiative lifetime extraction using power-dependent relative photoluminescence of III-V semiconductor double-heterostructures

A power-dependent relative photoluminescence measurement method is developed for double-heterostructures composed of III-V semiconductors. Analyzing the data yields insight into the radiative efficiency of the absorbing layer as a function of laser intensity. Four GaAs samples of different thicknesses are characterized, and the measured data are corrected for dependencies of carrier concentration and photon recycling. This correction procedure is described and discussed in detail in order to determine the material's Shockley-Read-Hall lifetime as a function of excitation intensity. The procedure assumes 100% internal radiative efficiency under the highest injection conditions, and we show this leads to less than 0.5% uncertainty. The resulting GaAs material demonstrates a 5.7 ± 0.5 ns nonradiative lifetime across all samples of similar doping (2–3 × 10^(17) cm^(−3)) for an injected excess carrier concentration below 4 × 10^(12) cm^(−3). This increases considerably up to longer than 1 μs under high injection levels due to a trap saturation effect. The method is also shown to give insight into bulk and interface recombination

Radiation hardness of AlGaAs n-i-p solar cells with higher bandgap intrinsic region

The radiation hardness of AlGaAs single-junction solar cells is investigated for various n-i-p solar cell designs. The material composition in both the n-p regions is varied between 3.5% and 16% Al-content, whereas the intrinsic region has a higher Al-content between 3.5% and 23%. The beginning-of-life and end-of-life quantum efficiency and current – voltage characteristics are discussed to establish trends as a function of material bandgap. It is found that, increasing the Al-content of AlGaAs tends to increase the radiation hardness of the solar cells up to an efficiency remaining factor of 85%. This enhancement mostly originates from an improved open circuit voltage remaining factor that is caused by a deterioration of the beginning-of-life performance as the Al-content increases. However, a degradation in photocurrent is observed for increasing Al content in the intrinsic region, which is partially due to minority carrier potential barriers at the base/intrinsic heterointerface. In general, increasing the bandgap of the intrinsic region improves radiation hardness, but the formation of potential barriers for minority carriers must be avoided. The diffusion lengths and damage coefficients are also extracted by modeling the quantum efficiency

Narrow spectral linewidth from single site-controlled In(Ga)As quantum dots with high uniformity

We present narrow spectral linewidth from single site-controlled In(Ga)As quantum dots (QDs) grown on nanoholes, which were defined by electron beam lithography on a (100) GaAs substrate. The long-range ordering of uncapped QDs is confirmed by electron microscopy whereas the ordering of capped QDs is visualized by atomic force microscopy. We find a small inhomogeneous broadening of 14.4 meV for the ensemble emission of site-controlled QDs with 300 nm lattice period. The photoluminescence from the excitonic transitions of single site-controlled QDs exhibits linewidth values down to 43 mu eV, which is promising for the investigation of pronounced cavity quantum electrodynamic effects in scalable QD-microresonator systems. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3568890]</p

Nonradiative lifetime extraction using power-dependent relative photoluminescense of III-V semiconductor double-heterostructures

A power-dependent relative photoluminescence measurement method is developed for double-heterostructures composed of III-V semiconductors. Analyzing the data yields insight into the radiative efficiency of the absorbing layer as a function of laser intensity. Four GaAs samples of different thicknesses are characterized, and the measured data are corrected for dependencies of carrier concentration and photon recycling. This correction procedure is described and discussed in detail in order to determine the material's Shockley-Read-Hall lifetime as a function of excitation intensity. The procedure assumes 100% internal radiative efficiency under the highest injection conditions, and we show this leads to less than 0.5% uncertainty. The resulting GaAs material demonstrates a 5.7 ± 0.5 ns nonradiative lifetime across all samples of similar doping (2–3 × 1017 cm−3) for an injected excess carrier concentration below 4 × 1012 cm−3. This increases considerably up to longer than 1 μs under high injection levels due to a trap saturation effect. The method is also shown to give insight into bulk and interface recombination

Site-controlled In(Ga)As/GaAs quantum dots for integration into optically and electrically operated devices

We investigated the growth and device integration of site-controlled In(Ga)As quantum dots (SCQDs) on a pre-patterned substrate. A high substrate temperature of 545 degrees C during growth ensures optimal SCQD nucleation on square arrays from 200 nm up to 10 mu m period. The SCQDs exhibit a small inhomogeneous broadening of the ensemble emission and a rather narrow single SCQD linewidth. We used a scalable alignment technique to integrate the SCQDs into a p-i-n diode and observe electroluminescence of a single SCQD with a linewidth of 400 mu eV. (C) 2010 Elsevier B.V. All rights reserved.</p