Recombination, diffusion rates and diffusion length in MAPbI₃ and MAPBr₃ crystals in a wide carrier density range: experiment and theory.

We applied time-resolved pump-probe spectroscopy based on free carrier absorption and light diffraction on a transient grating for direct measurements of the carrier lifetime and diffusion coefficient D in high-resistivity single crystal CdTe (codoped with In and Er). The bulk carrier lifetime τ decreased from 670 ± 50 ns to 60 ± 10 ns with increase of excess carrier density N from 10¹⁶ to 5 × 10¹⁸ cm⁻³ due to the excitation-dependent radiative recombination rate. In this N range, the carrier diffusion length dropped from 14 μm to 6 μm due to lifetime decrease. Modeling of in-depth (axial) and in-plane (lateral) carrier diffusion provided the value of surface recombination velocity S = 6 × 10⁵ cm/s for the untreated surface. At even higher excitations, in the 10¹⁹–3 × 10²⁰ cm⁻³ density range, D increase from 5 to 20 cm²/s due to carrier degeneracy was observed.

We explored a Mg-alloyed ZnO material (or MgZnO alloy) on a lattice-matched scandium aluminum magnesium oxide substrate for obtaining most effective photodetectors with highest (∼10 A/W) and fastest (up to 3 GHz) responses and two orders of magnitude UV/VIS rejection ratio. Device operation was related to its material electronic properties (carrier lifetime, diffusivity, and diffusion length) via photoluminescence and light-induced pump–probe techniques. Defect-related response is found suitable for sensitive logarithmic detectors, while exciton-related response is favorable to ultrafast linear UV solar blind detectors. Two-contact planar detector design allows their application in low-cost environmental detection systems.