Abstract
Past studies have demonstrated the positive impact of step-graded $p$ -type Al x Ga1− x N/GaN superlattice (SL) electron blocking layer (EBL) structures on the efficiency performance of ultraviolet (UV) GaN-based light-emitting diodes (LEDs). However, the optimal Al-grading structure of these SL EBLs remains unclear owing to a lack of systematic investigation. The present work addresses this issue by applying EBL composed of alternating half-peak, single-peak, and double-peak $p$ -type Al x Ga1− x N/GaN SL structures with varying values of $x$ ranging from 0.05 to 0.15 in 0.05 step increments. Simulation analysis is employed to obtain the internal quantum efficiency (IQE), energy band diagrams, polarization compensation factor, hole concentration, and electron concentration of GaN-based UV LEDs with three different SL-EBL structures. The results obtained at an injection current of 200 mA demonstrate that UV LEDs with double-peak SL-EBL structures provide the maximum IQE, which is ~38% greater than that of devices employing the conventional EBL in simulation experiment. This SL-EBL is demonstrated to improve the hole injection and electron overflow performance of GaN-based UV LEDs owing to the polarization charge and lattice mismatch at the p- Al x Ga1− x N/GaN interfaces. The reduced Al composition on the p- GaN side reduces the potential barrier of hole injection. Moreover, the predicted increase in the IQE of GaN-based UV LEDs with the optimal SL-EBL is verified experimentally.
Highlights
Ultraviolet light-emitting diodes (UV-LEDs) have generated intensive interest due to their many advantages compared to conventional UV mercury lamps, as well as their wide applicability in numerous applications such as in water purification, medical treatment, analytical sensing and high-density optical storage devices [1]–[4]
The application of double-sided, step-graded AlxGa1−xN electron blocking layer (EBL), with x being 5%, 10%, and 15% and a step width of 4 nm along each growth direction, improves internal quantum efficiency (IQE), optical output power, and nearly eliminating the droop in the IQE [12]. While these past studies have demonstrated the beneficial impact of stepgraded Alx Ga1−x N EBLs on the IQE droop of GaN-based LEDs, absolute enhancements in the IQE and optical output power of the devices remain limited because hole injection is affected by the downward band-bending induced by the serious polarization at the interface between the EBL and the last quantum barrier (QB) of the LED [13], [14]
This paper addresses this issue by evaluating the performance of GaN-based UV LEDs with alternating halfpeak, single-peak, and double-peak p-type Alx Ga1−x N/GaN SL-EBL structures with x values ranging from 0.05 to 0.15 in VOLUME 9, 2021
Summary
Ultraviolet light-emitting diodes (UV-LEDs) have generated intensive interest due to their many advantages compared to conventional UV mercury lamps, as well as their wide applicability in numerous applications such as in water purification, medical treatment, analytical sensing and high-density optical storage devices [1]–[4]. The application of double-sided, step-graded AlxGa1−xN EBL, with x being 5%, 10%, and 15% and a step width of 4 nm along each growth direction (from the last QW to p-AlGaN), improves internal quantum efficiency (IQE), optical output power, and nearly eliminating the droop in the IQE [12] While these past studies have demonstrated the beneficial impact of stepgraded Alx Ga1−x N EBLs on the IQE droop of GaN-based LEDs, absolute enhancements in the IQE and optical output power of the devices remain limited because hole injection is affected by the downward band-bending induced by the serious polarization at the interface between the EBL and the last QB of the LED [13], [14]. The predicted increase in the IQE of GaN-based UV LEDs with the optimal SL-EBL structure is verified experimentally
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