Abstract
The lower luminous efficiency is a critical issue for ultraviolet light-emitting diodes (UV-LEDs) owing to the poor carrier injection efficiency and high dislocation density. Here, we can improve the luminous efficiency in two avenues by adjusting the Al composition of the InGaN/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> N pre-well superlattice. First, due to the strain-induced piezoelectric and intrinsic spontaneous polarization, a large number of electrons gather at the InGaN/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> N interface, which improves the electron concentration of the pre-well superlattice and lowers the conduction band energy of the first quantum barrier layer (FQB), thus enhancing the electron injection efficiency. Second, the pre-well superlattice can act as a hole blocking layer to prevent holes from leaking into the n-type layer and confine them in the quantum well layer. As the Al composition increases, the hole blocking effect of the pre-well superlattice is strengthened. However, higher Al composition decreases the lattice quality, which makes it possible for carrier loss through defect-related non-radiative recombination. Finally, the output power of the samples with 5% Al composition in the pre-well superlattice is 5.9% and 102.5% higher than that of the samples with 3% and 7% Al composition, respectively.
Highlights
In the last few years, ultraviolet light-emitting diodes (UV-LEDs) have received a lot of attention for their wide applications [1]-[2]
We mainly focus on how to improve the luminous efficiency by adjusting the Al composition of the InGaN/AlxGa1-xN pre-well superlattice inserted between the n-type layer and multiple quantum wells (MQWs)
This indicates that the pre-well superlattice acts as an HBL to prevent holes from leaking to the n-type region, which allows more holes to participate in radiative recombination in MQWs
Summary
In the last few years, ultraviolet light-emitting diodes (UV-LEDs) have received a lot of attention for their wide applications [1]-[2]. It is well known that the polarization-induced electric field between the last quantum barrier layer (LQB) in MQWs and the p-type layer lowers the energy band at the interface, causing electrons to leak into the p-type, thereby participating in non-radiative recombination [10]. Various approaches, such as employing high Al composition AlGaN electron blocking layer (EBL) [11], graded EBL [12], insertion layer in EBL [13], and multi-quantum barriers EBL [14], have been put forward to cope with this problem. Compared to our previously reported samples with double superlattices and Si modulation-doped AlGaN/GaN, the optical power of UV-LEDs with the pre-well superlattice is increased by 62 % and 72.7% at 120 mA, respectively
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