Electronic and nonlinear optical properties of dielectric-encapsulated concentric quantum nano-rings for tunneling devices in microelectronics under axial electric field

Abstract

Addressing critical challenges in quantum device engineering and tunneling phenomena, this meticulous study theoretically scrutinizes the optical absorption coefficients (OACs) as well as the refractive index changes (RICs) resulting from intersubband transitions in a concentrically coupled nano-quantum ring (CCNQR). We mainly focus on the impact of in-situ structural parameters (inner radius, height, inner and outer ring widths), electric field, incident optical intensities and the choice of oxidized dielectric environment (SiO₂ vs. HfO₂). Under the framework of the effective mass approximation and the compact density matrix approach, the subband energy eigenvalues and their associated wavefunctions were determined by solving the time-independent Schrödinger equation. Contrary to other studies reported in the literature, we took into account the conduction band discontinuity that originates at the system and its surrounding medium, as well as the dielectric mismatch. Our findings demonstrated a strong correlation between quantized energies, dipole moments and the key structural metrics as well as the applied external electric field. Incorporating the electric field and surrounding oxides into our calculations resulted in a significant alteration of the probability amplitude and spatial distribution of the wavefunction by exhibiting two distinct regimes: coupled and decoupled. Our major outcomes revealed that when F = 30 KV/cm, the dipole moment is 1.42 times larger when choosing the HfO₂. We found that the OAC’s resonant peak has reached 7,2 × 10⁵ m^-1 (8.6 × 10⁵ m^-1) in case of SiO₂ (HfO₂). In addition, for HfO₂ (SiO₂), the photobleaching phenomenon was observed at an intensity of I = 0.2 MW/cm² (I = 0.4 MW/cm²). We conclude that the resonance frequencies as well as the intensity of the nonlinear optical attributes are roughly tunable through geometric factors and the electric field, while fine-tuning could be achieved through a careful choice of the surrounding oxidative layer.