Effects of internal electrical field on transient absorption in ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ thin layers and quantum wells with different thickness by pump and probe spectroscopy

The well width dependence of internal electric field effects was investigated using nondegenerate pump and probe spectroscopy at low and room temperature in four types of InGaN-based semiconductors of active layer thicknesses (a) 30 nm (single layer), (b) 10 nm (3 periods), (c) 5 nm (6 periods), and (d) 3 nm (10 periods). For sample (a) and (b) photoinduced absorption was observed due to screening of the internal electric field at low and room temperature. We observed two competing effects, exciton localization and the internal electric field, in sample (c) at low temperature. For sample (d) only photobleaching was observed due to occupation at the localized states. The results show that the field screening effects are more important for increasing well width after carrier generation. Furthermore, the carrier density to observe the photoinduced absorption due to screening the internal electric field is much less than the carrier density for stimulated emission at room temperature.