Excitation-dependent photoluminescence and photoreflectance in InGaAs/GaAs quantum dot bilayers: Comparison of undoped and n-doped configurations

Temperature- and excitation-dependent photoluminescence (PL) and photoreflectance (PR) spectroscopy were employed to investigate carrier dynamics and internal electric-field effects in undoped and nominally n-doped InGaAs/GaAs quantum dot (QD) bilayer structures composed of uncapped surface and buried QDs. By using UV, green, and red excitation/modulation wavelengths, surface-sensitive, intermediate-depth, and bulk-mediated carrier-generation regimes were selectively probed within the same heterostructure. Systematic differences between the undoped and doped configurations were observed across all excitation conditions. The doped structure exhibited enhanced PL intensity, reduced sensitivity to state-filling effects, and a progressively significant contribution from electric-field–related modulation mechanisms. Under deep excitation conditions, QD-related PR features and Franz–Keldysh oscillations persisted up to room temperature exclusively in the doped sample, indicating a more stable internal electric-field configuration under thermally activated carrier redistribution. The combined PL and PR analysis indicates that moderate n-type doping at the single-electron-per-dot level primarily modifies the balance between population-driven and field-driven optical processes, rather than introducing additional non-radiative recombination pathways. These findings highlight the role of low-level doping in controlling carrier redistribution and internal electric fields in QD heterostructures, parameters that are critical for the performance of temperature- and excitation-dependent optoelectronic devices.