Abstract
Achieving high conductivity in n-type AlGaN of deep ultraviolet light-emitting diodes is still a challenge nowadays. In the Lei–Ting equilibrium equation method framework, a four-layer quantum well with n-Al0.7Ga0.3N barriers and an Al0.55Ga0.45N/AlxGa1−xN bi-component well could obtain a much higher electron mobility μT than that in a single-component quantum well over a relatively broad Al content range 0.56 < x < 0.68. While the built-in electric field induces strong confinement, pushing the electron to the interface, the optical phonon mode at this interface could be component-modulated to disappear due to the ternary mixed crystal effect. A significant enhancement of electron mobility can be achieved by avoiding the scattering from optical phonons at the interface where the electron gathers. The optical phonon limited μT could reach 7966 cm2/V s at x = 0.58, which is almost five times of 1518 cm2/V s in the case of x = 0.55 and ten times of 822 cm2/V s for x = 0.70. Such a step-shaped quantum well with high electron mobility could be an alternate or insert layer to the high Al content n-layer to alleviate the current crowding.
Highlights
The n-layer in deep ultraviolet (DUV) light-emitting diode (LED) serves as both the light extraction and the electron transport layer connecting to the electrodes
The results indicate that much higher electron mobility in the stepped quantum well (QW) with a relatively wide component region than in a single QW
Since electrons are firmly bound near interface 1 and hardly tunnel into the barrier, they are scarcely scattered by the HS and PR optical phonons but mostly scattered by the IF and contained.24 They are quasiconfined (CO) optical phonons, which are carefully considered in this work
Summary
The AlGaN-based deep ultraviolet (DUV) light-emitting diode (LED) with high internal quantum efficiency has become one of the most promising alternatives to mercury lamps as the new generation of ultraviolet light sources. many obstacles restrict the external quantum efficiency from reaching the blue light band. The low conductivity in the n-AlGaN layer is one of them in a typical mesa-type LED. The n-layer in DUV LEDs serves as both the light extraction and the electron transport layer connecting to the electrodes. The first type is based on an approximate formula of the current spreading length given by Guo and Schubert, including modifying electrode patterns to realize multichannel electronic transmission perpendicular to the surface of mesa and adjusting the side resistance to extend the current spreading length.13,14 It improves the current blocking on the top of the n-doped layer as the electronic transfer next to the electrode. The results indicate that much higher electron mobility in the stepped QW with a relatively wide component region than in a single QW is achievable by avoiding the scattering from the IF phonons
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