| dc.description.abstract | Because of its short wavelength, ultraviolet(UV) LEDs have been applied in various fields including water and air purification, medical hygiene, and more. However, the low luminous efficiency of UV LEDs has hindered their penetration into the market. One of the reasons for the low luminous efficiency is the polarization of AlGaN quantum wells. When the quantum wells are subjected to polarization effects, the induced Quantum Confined Stark Effect (QCSE) creates an internal electric field, leading to the separation of electrons and holes, thus reducing the radiative recombination efficiency. To reduce the QCSE, we adopt cubic boron nitride (c-BN) in the growth of UV LEDs.
The UV LED, with c-BN inserted under the AlGaN multiple quantum wells (MQWs), was grown by metal-organic chemical vapor deposition (MOCVD) on two-inch sapphire substrates. Characterization of electroluminescence (EL) spectra and current-voltage curves showed that the UV LED with c-BN did not emit light. According to the band diagram simulated by the one-dimensional drift-diffusion charge control solver (1D DDCC), election injection from the n-type AlGaN was blocked by the large bandgap (~6.2eV) of c-BN. In order to increase the injection efficiency, the c-BN layer was moved from MQWs/c-BN/n-AlGaN to MQWs/n-AlGaN/c-BN. In the simulated band diagram of MWQs/n-AlGaN/c-BN, the electron-blocking band offset at c-BN/n-AlGaN is removed, and the band tilting of MQW is also likely to be mitigated. | en_US |