To prevent electron leakage in deep ultraviolet (UV) AlGaN light-emitting diodes (LEDs), Al-rich p-type AlxGa(1−x)N electron blocking layer (EBL) has been utilized. However, the conventional EBL can mitigate the electron overflow only up to some extent and adversely, holes are depleted in the EBL due to the formation of positive sheet polarization charges at the heterointerface of the last quantum barrier (QB)/EBL. Subsequently, the hole injection efficiency of the LED is severely limited. In this regard, we propose an EBL-free AlGaN deep UV LED structure using graded staircase quantum barriers (GSQBs) instead of conventional QBs without affecting the hole injection efficiency. The reported structure exhibits significantly reduced thermal velocity and mean free path of electrons in the active region, thus greatly confines the electrons over there and tremendously decreases the electron leakage into the p-region. Moreover, such specially designed QBs reduce the quantum-confined Stark effect in the active region, thereby improves the electron and hole wavefunctions overlap. As a result, both the internal quantum efficiency and output power of the GSQB structure are ~2.13 times higher than the conventional structure at 60 mA. Importantly, our proposed structure exhibits only ~20.68% efficiency droop during 0–60 mA injection current, which is significantly lower compared to the regular structure.
Electron overflow from the active region confines the AlGaN
deep-ultraviolet (UV) light-emitting diode (LED) performance. This
paper proposes a novel approach to mitigate the electron leakage
problem in AlGaN deep-UV LEDs using concave quantum barrier (QB)
structures. The proposed QBs suppress the electron leakage by
significantly reducing the electron mean free path that improves the
electron capturing capability in the active region. Overall, such an
engineered structure also enhances the hole injection into the active
region, thereby enhancing the radiative recombination in the quantum
wells. As a result, our study shows that the proposed structure
exhibits an optical power of 9.16 mW at
∼
284
n
m
wavelength, which is boosted by
∼
40.5
%
compared to conventional AlGaN UV LED
operating at 60 mA injection current.
One of the probable reasons behind the limitation of light extraction efficiency (LEE) in III-nitride nanowire (NW) deep ultraviolet (UV) light-emitting diodes (LEDs) is the presence of the high surface density states that significantly contribute to the non-radiative recombination near the surface. Herein, we investigate the LEE of a single AlInN NW UV LED in the entire UV wavelength regime using finite-difference time-domain simulations. It is found that these LEDs favor transverse-magnetic (TM) polarized LEE over transverse-electric (TE) polarized emission. Further, we examine the role of the HfO2 surface passivation layer in the improvement of LEE of AlInN NW LED at ~282 nm wavelength. Our results show that the TM-polarized LEE of such LED without any passivation is only ~25.2%, whereas the maximum recorded LEE is ~40.6% with the utilization of 40 nm HfO2 passivation layer. This study provides a promising approach for enhancing the LEE of NW UV LEDs.
The formation of positive sheet polarization charges at the interface of the last quantum barrier (QB) and the conventional
p
-type electron-blocking layer (EBL) creates significant band bending, leading to severe electron leakage and poor hole injection in III-nitride light-emitting diodes. We report that the positive sheet polarization charges are mitigated by employing a lattice matched AlGaN last QB. Electron leakage is dramatically reduced due to the increased effective conduction band height at the last QB and EBL. Furthermore, it favors hole injection into the active region due to the reduced effective valance band height for EBL.
Thermal imaging by an infrared television camera has been successfully employed as an in situ method for end-point detection during plasma etching of polycrystalline silicon layers on a SiO2/Si substrate. In addition, it is also shown that thermal imaging can be used for remote sensing of etch rate, heat of reaction, wafer temperature, and for measuring thermal time constants during plasma etching. From these measurements, the heat-transfer coefficient of the thermal contact between the silicon wafer and the water-cooled electrode can be determined.
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