Moreover, nitrogen increases
the density of nonradiative recombination centers in the bandgap which strongly contributes to the carrier lifetime. Annealing indeed increases the decay time of GaInNAs, and this is shown in Figure 3, Apoptosis antagonist where the as-grown sample decay time is also plotted. Lifetime increases by one order of buy GSK2118436 magnitude following RTA, underlining the importance of thermal annealing for dilute nitride solar cells. Optimal annealing conditions for GaInNAs depend on the amount of nitrogen and growth parameters. Typically, good results for solar cells are obtained when annealing is performed at 750°C to 800°C for a few hundred seconds [24, 25]. This significant increase of decay time is related to reduction of nonradiative recombination and removal of defects due to thermal annealing [26, 27]. Furthermore, the decrease of decay times for the higher nitrogen content points out to the fact that that nitrogen-related defects are responsible for decreasing the carrier lifetime . Figure 3 Decay time versus wavelength for as-grown and annealed Neuronal Signaling inhibitor sample 1. The effect of RTA was further investigated on the GaNAsSb structure. Figure 4 shows TRPL decays for sample 4 for as-grown wafer and annealing
times of 300 and 1,800 s at a temperature (T ann) of 750°C. The dependences of decay time on detection wavelength are presented in Figure 5. An increase in decay time is observed when moving towards the band edge, which is similar to samples 1 to 3. The change in the τ(λ) slope upon RTA can be linked to carrier energy relaxation processes in the vicinity of the conduction band edge . Although lifetime increases with annealing, it remained below 100 ps. Furthermore, sample 4 has AlInP
window layer which suppresses effectively surface recombination rates. This lifetime is approximately one fourth of that for sample 3 and one half of the value obtained for the quinary GaInNAsSb . Furthermore, as high as 900 ps, lifetime (not shown) was measured from an optimized GaInNAs p-i-n solar cell structure with an approximately 1.15-eV bandgap . The fact that the lifetime after annealing is one order of magnitude less than for optimized GaInNAs and less than what has been Etofibrate published for GaInNAsSb indicates that there is still room for further optimization for GaNAsSb growth and annealing parameters. Figure 4 Decay profiles for sample 4 comprising GaNAsSb measured at λ = 1,250 nm. Annealing time at T ann = 750°C was 0, 300, and 1,800 s. Figure 5 Wavelength-dependent decay times τ for sample 4 with GaNAsSb i-region. Annealed at T ann = 750°C for 0, 30, and 1,800 s. Conclusions We investigated the carrier lifetime dynamics in lattice-matched GaInNAs and GaNAsSb p-i-n solar cells using TRPL.