A. Study on the effect of Luminous power
In any numerical-based simulation, validation of the simulation with the experimental result is essential as it ensures the correctness of the simulation. Therefore, the experimentally reported InGaN/GaN LED structure in [18] is simulated in TCAD physical simulator. The simulated and experimental output light power in [22] is shown in Fig. 2. It is verified that the simulated results fit well with experimental data. Therefore, the simulation is calibrated well and realistic. To examine the electrical properties of the device, the numerical simulation makes use of the current continuity, Poisson, carrier transport, and heat transfer equations. The optical gain parameters of the device are examined using the Schrodinger and quantum mechanical wave equations. Once the simulation calibrated, the same simulation setting is used to analyse the proposed and conventional LED in this paper.
The experimental data is reported in [18]. The quantum behavior of the carriers in the sub-band energy levels mainly depends on the formation of the quantum well and its thickness. Therefore, it is essential to verify whether the quantum well is formed in the simulated structure or not. Figure 3 shows that the quantum well is formed for both proposed and conventional devices. The valence band of the proposed LED is shifted upwards when compared to conventional LED due to quantum confinement and photon excitation, in which more holes are available for the recombination process tends to have high luminous power. This ensures that the simulation is realistic.
The anode voltage of GaN LED is swept and luminous power is observed. Figure 4(a) shows the luminous power over the anode voltage. It observed that the InGaN light emitting diode works at a large bias voltage of 3.3 V, which is consistent with the bias voltage reported in [29]. This large bias does not allow the band to be flat. Rather, the band edges are tilted by the polarization-induced electric field. Furthermore, approaching the threshold voltage, the optical power of the proposed InGaN/GaN LED and the standard InGaN/GaN LED is the same. The luminous power of the proposed device is higher than that of the conventional device at higher bias (a little beyond threshold voltage). Figure 4(b) shows the electrical performance of GaN LED. In the conventional LED, the increase in the forward voltage increases exponentially the current through the LED. Whereas in the proposed device, the introduction of HfO2 layer alters the voltage characteristics. The below graph shows the increased forward voltage of 2.9 V at 30 mA current.
The luminous power as a function of injection current is calculated and shown in Fig. 5. When compared to LEDs without a p-GaN cap layer, the suggested InGaN/GaN LED with a p-GaN cap layer has a higher luminous power. It is attributed to the proposed device's increased radiative rate, which is discussed in the subsequent section.
B. Study on the effect of recombination rate
The key mechanism in the light-emitting diode is recombination process. More specifically, the radiative recombination process. As shown in Fig. 6, the radiative rates of the proposed and conventional InGaN/GaN LEDs are compared. The proposed device's radiative rate is found to be improved. It is due to the presence of GaN layer closer to the quantum well.
The radiative recombination process is desirable for a light-emitting diode. The SRH and Auger recombination processes, on the other hand, are unfavourable for LEDs. Because the SRH and Auger recombination processes produce phonons rather than photons, phonons are produced. The LED's Auger recombination process is depicted in Fig. 7. It is found that Auger recombination rate in the proposed device is lower. It is a welcome feature for the proposed device.
The comparison analysis of radiative recombination is made for the conventional and the proposed InGaN/GaN LED is shown in the Fig. 8. It is evident that the recombination rate is increased with the effect of depth of the quantum wells.
C. Study on the effect of current densities in Multiple Quantum Wells
The injection of electrons and holes could be analysed using the current density in LED. Figure 9 depicts the current density in the simulated LED. The current density is higher in the well region. It's related to the well region's localization of holes and electrons. Furthermore, the proposed LED has a higher current density due to the presence of HfO2 layer. The HfO2 layer reduces the interface trap densities, resulting in more carrier confinement in that region leading to high current density. Therefore, the radiative recombination rate of the proposed is enhanced, which is shown in the above Fig. 8. This clearly shows that the proposed device's carrier injection efficiency is higher than that of ordinary conventional LEDs. The color difference in Figs. 9 & 10 shows the current density and potential is changed by HfO2 and p-GaN.
The potential spread of the proposed and conventional light-emitting diode is shown in Fig. 10. It is evident that the use of the GaN layer adjacent to the quantum well changes the potential spread. Consequently, the electric field is affected by the potential distribution. The effect in the electric field impacts the drift current density (J)
\(J=nq{\mu }_{n}E+pq{\mu }_{p}E\) (x1)
where, n and p are electron and hole concentrations, respectively. The \({\mu }_{p}\) and \({\mu }_{n}\) are hole and electron mobility, respectively. The q and E are the electronic charge and electric field respectively. From Eq. x1, it is clear that the change in the potential or electric field is responsible for the change in current density. This change in current density is shown in Fig. 9.
D. Study on the effect of photoluminescence
Figure 11 shows the photoluminescence (PL) intensity of conventional and proposed InGaN/GaN LED. The trend of PL intensity is consistent with reported data in [21]. Both conventional and proposed LED peaks at 460 nm. Further, at the wavelength of 460 nm, the peak intensity of conventional and proposed LED are 1.16 and 1.45, respectively. The PL indensity in propsed LED is improved by 20% compared to the convention LED. It is due to more number of injection of carriers in the proposed LED.
E. Study on the Effect of Internal Quantum Efficiency
One of the most essential figures to consider when evaluating LED performance is internal quantum efficiency. The amount of radiative recombination occurring inside the quantum well divided by the overall number of carriers pumped into the LED is known as internal quantum efficiency. In any case, the ABC model often explains it as the percentage of injected current that transforms into photon production in the active zone. As a result, the internal quantum efficiency is analyzed. This is extracted using radiative, SRH and Auger recombination rate. For this, the extraction statement is used in TCAD simulator. The extracted IQE of the proposed and conventional InGaN/GaNLED is depicted in Fig. 12. It is observed that the IQE of the proposed InGaN/GaN LED is higher than that of conventional InGaN/GaN LED. It is due to the lower Auger recombination rate in the proposed LED as shown in Fig. 7.
Further, in order to show the improvement in the proposed device, the performance metrics are contrasted with the conventional InGaN/GaN LED in Table 2. As can be seen, the proposed device shows improved output luminous power, radiative rate, and internal quantum efficiency at the injection current of 700 mA. Therefore, the proposed InGaN/GaN LED device is suitable for solid-state lightingapplications. The Performance comparision of conventional and proposed InGaN/GaNLED is highlighted in Table 2.
Table 2
Performance Comparision of Conventional and proposed LED
Parameters | Conventional LED | Proposed LED |
Radiative rate (cm-3 s-1) | 3.51×1019 | 4.42×1019 |
Luminous output power (W) | 1.6 | 2.1 |
Internal quantum efficiency (%) | 56 | 68 |