Modeling of the optical gain in ZnO-based quantum cascade lasers

ZnO has been proposed recently as a good base material for high-power terahertz quantum cascade lasers (QCLs) operating at room temperature. We have developed a theoretical model for calculation of the optical gain, based on solving the system of rate equations and taking into account relevant scattering mechanisms. This model has been implemented to perform numerical simulations using ZnO/ZnMgO material combination, starting from the conventional design with three well within the active region of the structure. The influence of the layer widths and composition on the output properties has been considered, together with the variation of the number of quantum wells per QCL period.XVIII Young Researchers' Conference Materials Sciences and Engineering : program and the book of abstracts; December 4-6, 2019; Belgrad

Investigation of intersubband transitions in wide bandgap oxide quantum well structures for optoelectronic device applications

There has been a surge of interest in recent years for the advancement of wide bandgap oxides such as zinc oxide (ZnO), magnesium oxide (MgO), gallium oxide (Ga2O3), etc. [1,2]. These materials have gained significant attention due to their distinctive characteristics and properties which are promising for the development of high-performance optoelectronic devices for applications in the domains of sensing, communications, and imaging. More specifically, Ga2O3 has wide bandgap energy of approximately 4.8 to 4.9 electron volts (eV), thus exhibiting exceptional transparency to ultraviolet (UV) radiation while displaying opaqueness to visible light [3]. On a parallel note, ZnO shows exemplary optical and electrical properties, including a high exciton binding energy and substantial oscillator strength [4]. Of particular significance is the exploration of intersubband transitions within multiple quantum well (MQW) structures, which offers a promising path for efficient light absorption and emission in the mid-infrared to terahertz spectral range. In this contribution we will numerically simulate the absorption spectra of the wide bandgap oxide MQW structures, adapting the approach for treating the light-matter interaction suitable when the depolarization field is the dominant many-body contribution, and discuss the potential applications in optoelectronic devices, specifically mid-infrared detectors, quantum cascade lasers, and modulators.IX International School and Conference on Photonics : PHOTONICA2023 : book of abstracts; August 28 - September 1, 2023; Belgrad

Numerical modeling of new oxide-based heterostructures for use in QCL devices

Semiconductor devices operating in the terahertz (THz) and near/mid infrared (IR) parts of the optical spectrum have been continuously explored and improved during the previous two decades [1-3]. Multiple new material platforms are being experimentally and theoretically investigated as candidates for room temperature operation of THz devices. One of the materials under recent consideration is ZnO due to its wide direct bandgap and high exciton binding energy. In this contribution we illustrate the use of a modified version of the Newton-Raphson method to numerically and self-consistently solve a system of SchrödingerPoisson equations for a structure consisting of coupled ZnObased quantum wells. The results obtained are compared with the experimental data available in the literature, after which the Additionally, the impact of the external electric field applied to the structure is assessed in order to determine the doping profile and well/barrier thicknesses that would be most promising for quantum cascade laser applications. Finally, we evaluate the absorption due to intersubband transitions between the bound states.XV Photonics Workshop : book of abstracts; March 13-16, 2022; Kopaoni

Modeling of intersubband transitions in ZnO/ZnMgO Coupled QuantumWells

In recent years ZnO has become a popular semiconductor withmany potential applications in infra-red and THz optical devices owing to awide direct bandgap (3.4 eV) in combination with relatively high exciton binding energy (60 meV) [1]-[2]. In this work, we model the electronic structure of coupled oxide-semiconductor quantum wells by numerically solving the system of coupled Schrödinger-Poisson equations self-consistently (Fig. 1).We compare the obtained results with the recent experimental data[3] and analyze howthe variation of the layers’thicknesses affects the energy states. In addition, we examine the influence of doping to assess the differences between single well and two wells’cases, for the purpose ofdesigning more complex multi-well optical system in the future.VIII International School and Conference on Photonics & HEMMAGINERO workshop : program and the book of abstracts; August 23-27, 2019; Belgrad

Modeling of optical properties of novel terahertz photonics quantum well heterostructures

In this contribution, we present our recent work on modeling intersubband transitions in the conduction band of semiconductor-based quantum well structures [1], [2]. Particularly interesting are possibilities offered by ZnO/ZnMgO and La-doped BaSnO3/BaO perovskite-oxide for the realization of room temperature oxide-based THz quantum well optoelectronic devices due to their advantageous physical and chemical properties [3], [4]. The electronic structure is calculated self-consistently by solving the Schrödinger–Poisson system of equations. A significant change of the transition energy due to the depolarization shift is also considered in cases when high doping is present. The charge-induced coherence due to the strong dipole-dipole Coulomb interaction between intersubband transitions leads to the formation of multisubband plasmons and a complete quantum model [5] based on the dipole representation must be used to calculate absorption spectra.XVI Photonics Workshop : book of abstracts; March 12-15, 2023; Kopaoni

Resonant tunnelling and intersubband optical properties of ZnO/ZnMgO semiconductor heterostructures: impact of doping and layer structure variation

ZnO-based heterostructures are up-and-coming candidates for terahertz (THz) optoelectronic devices, largely owing to their innate material attributes. The significant ZnO LO-phonon energy plays a pivotal role in mitigating thermally induced LO-phonon scattering, potentially significantly elevating the temperature performance of quantum cascade lasers (QCLs). In this work, we calculate the electronic structure and absorption of ZnO/ZnMgO multiple semiconductor quantum wells (MQWs) and the current density–voltage characteristics of nonpolar m-plane ZnO/ZnMgO double-barrier resonant tunnelling diodes (RTDs). Both MQWs and RTDs are considered here as two building blocks of a QCL. We show how the doping, Mg percentage and layer thickness affect the absorption of MQWs at room temperature. We confirm that in the high doping concentrations regime, a full quantum treatment that includes the depolarisation shift effect must be considered, as it shifts mid-infrared absorption peak energy for several tens of meV. Furthermore, we also focus on the performance of RTDs for various parameter changes and conclude that, to maximise the peak-to-valley ratio (PVR), the optimal doping density of the analysed ZnO/Zn88Mg12O double-barrier RTD should be approximately 1018 cm−3, whilst the optimal barrier thickness should be 1.3 nm, with a Mg mole fraction of ~9%

Calculation of intersubband absorption in ZnO/ZnMgO asymmetric double quantum wells

ZnO based heterostructures have recently received increased research attention, related to the development of room temperature THz/MiR semiconductor devices. The potential for these applications stems from the combination of wide direct bandgap and high exciton binding energy. In this work, we focus on the intersubband transition between bound states in the conduction band, and apply self-consistent numerical modelling to a system of Schrödinger–Poisson equations to evaluate the electronics structure of coupled semiconductor quantum wells. We subsequently analyse the fractional optical absorption at room temperature, as it varies with layers’ thicknesses, doping density and external electric field magnitude