Increasing the hole energy by the p-type dual polarization for high internal quantum efficiency of 237 nm-band deep ultraviolet light-emitting diodes

Abstract

Aluminum-rich p-AlGaN electron-blocking layers (p-EBL) usually block the hole injection in the AlGaN-based deep ultraviolet (DUV) light-emitting diode (LED). Meanwhile, the ionization energy of the magnesium receptors in the aluminum-rich p-AlGaN layer is considerably high, and the conductivity is low, leading to a reduction in the hole injection capability. Consequently, AlGaN-based DUV LEDs suffer from a low internal quantum efficiency (IQE). A structure of p-EBL and hole source layer (p-HSL) using AlN composition gradient AlGaN is proposed. The polarization bulk charges are introduced in both p-EBL and p-HSL (the p-type dual polarization) to shield the polarization-induced electric field and increase the hole energy. Although the single-polarized structure of p-EBL or p-HSL can also effectively enhance the performance of the device, calculation results indicate that the performance of the p-type dual-polarized structure can be doubled. This is because optimizing a single p-EBL or p-HSL can only introduce polarization bulk charge in the monolayer but not in all p-type regions. Therefore, in LEDs with shorter wavelengths, to maximize the hole energy, a dual-polarization structure should be adopted for the p-type region. Based on this, a maximum IQE of 55.65% and an efficiency droop of 4.84% are obtained at a wavelength of 237 nm. Findings of this study provide insights to solve the problem of low IQE in high-performance DUV LEDs.