Calculating the Effect of AlGaN Dielectric Layers in a Polarization Tunnel Junction on the Performance of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes

In this work, AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) with AlGaN as the dielectric layers in p+-Al0.55Ga0.45N/AlGaN/n+-Al0.55Ga0.45N polarization tunnel junctions (PTJs) were modeled to promote carrier tunneling, suppress current crowding, avoid optical absorption, and further enhance the performance of LEDs. AlGaN with different Al contents in PTJs were optimized by APSYS software to investigate the effect of a polarization-induced electric field (Ep) on hole tunneling in the PTJ. The results indicated that Al0.7Ga0.3N as a dielectric layer can realize a higher hole concentration and a higher radiative recombination rate in Multiple Quantum Wells (MQWs) than Al0.4Ga0.6N as the dielectric layer. In addition, Al0.7Ga0.3N as the dielectric layer has relatively high resistance, which can increase lateral current spreading and enhance the uniformity of the top emitting light of LEDs. However, the relatively high resistance of Al0.7Ga0.3N as the dielectric layer resulted in an increase in the forward voltage, so much higher biased voltage was required to enhance the hole tunneling efficiency of PTJ. Through the adoption of PTJs with Al0.7Ga0.3N as the dielectric layers, enhanced internal quantum efficiency (IQE) and optical output power will be possible.

FEATURES OF SELECTING DIELECTRIC LAYERS FOR ELECTROLUMINESCENT STRUCTURES

The paper considers an equivalent scheme of a thin-film electroluminescent emitter (TFELE), taking into account dielectric leaks, and proposes a criterion for the optimal choice of a dielectric in the structure to increase its efficiency. A calculation method is proposed for the optimal choice of material for dielectric films in an electroluminescent structure, taking into account their dielectric loss tangent. The algorithm for optimizing the parameters is based on the method of pairwise comparison of two dielectrics, provided that the charge flowing through the structure is constant or increased. The calculated data for materials are given in the form of a table according to the sequence of deterioration of their characteristics. The most attractive of the materials considered are PbTiO3, Ta2O5, Y2O3, as well as improved ceramics, which is confirmed by experiment. The possibility of applying the proposed model to explain the dependence of the luminosity of electroluminescent emitters on their excitation voltage is shown. A comparative analysis of the results of the calculation and experiment of the dependence of brightness on the applied voltage (B-V) for three types of TFELE based on a luminescent layer ZnS : Mn (0.5%) with a thickness of 0.6 μm, placed between two dielectric layers with a thickness of about 0.3- 0.35 μm with Ta2O5, Sm2O3 and Y2O3, respectively. It is established that the threshold luminescence excitation voltage correlates with the value of εE, and the maximum brightness with the value of εE / tg (δ). The table also shows the calculated characteristics of NdAlO3 and AlN films deposited by high-frequency magnetron sputtering. Higher brightness values can be expected from electroluminescent structures with such a dielectric than from structures with dielectric films with Sm2O3 and Y2O3. The results of such studies are presented in the form of a graph and table. This method can find practical application in the development of new materials and technologies for their production.

Influence of dielectric overlayers on self-heating of a microdisk laser

We studied experimentally and numerically self-heating of a microdisk laser developed in the AlGaInAs material system and covered with dielectric layers. By experiments, we found that planarization of the microlaser with SU-8 photoresist significantly (almost, 2-fold) decreases the microlaser thermal resistance. Calculations demonstrate that a downward heat flux through the substrate to the heat sink is a dominant way of heat dissipation, and upward convection is much less relevant. Also, the calculations showed that covering microlaser with a TiO2 layer barely affects microdisk temperature but decreases heat localization in the structure.

Kelvin-probe microscopy as a technique of estimation of the charge traps saturation time

In this work, a method for estimating the saturation time of traps in dielectric layers based on the KPM is proposed. Using hafnium oxide layers as an example, it is shown that when charging with a series of points with different durations, a different dependence of the residual potential on time is observed. It is assumed that this technique makes it possible to evaluate the performance of devices based on dielectric layers.

Extending the absorption band from infrared to ultraviolet using the ITO transition from reflection to transparence

A numerical simulation based on the finite-element method shows that a metamaterial absorber using Tungsten (W) and Indium tin oxide (ITO) plasmonic metals can be ultra-broadband and high-performance. Conventional broadband absorbers usually consist of multiple metal-dielectric layers or multi-resonators and have a bulky shape. The present investigates the possibility to reach optimal characteristics with a simple design by combining two plasmonic materials (W/ITO) within a single resonator. Involving the ITO transition from reflection to transparence dramatically increases the absorption bandwidth, which is extended from infrared to ultraviolet, with up to 99.92% absorption. The design is polarization-insensitive under oblique incidence, up to 75° and 80°, for TE and TM polarization waves, respectively.