| Summary: | 碩士 === 國立中央大學 === 光電科學與工程學系 === 107 === ENGLISH ABSTRACT
Ultraviolet (UV) light-emitting diodes (LEDs) have replaced conventional UV light sources in various applications. Nevertheless, deep-ultraviolet light-emitting diodes (DUV LEDs, λ ≤ 290nm) are still intensively investigated because of its low EQE remaining below 10% [2]. In particular, AlGaN alloys have been the most common material for DUV LEDs. In spite of continuous efforts to develop an AlGaN DUV LED, its EQE is still typically below 10%. The limitation roots in the low conductivity of p-AlxGa1-xN as its activation energy for Mg acceptor is very high (170meV to 510meV) [6]. The high activation energy of Mg acceptor leads to low hole injection efficiency. Among many approaches have been utilized to enhance DUV LEDs’s EQE, Boron Nitride (BN) has emerged as a promising candidate to substitute p-type AlGaN in DUV LEDs. Due to its layered structure, BN has high chemical and thermal stability. Besides that, with large bandgap (~6eV), it becomes a suitable material to be used as an electron blocking layer by causing a large conduction band offset and a smaller valence band offset with other III-V materials [8,9]. The most outstanding property of BN is the dramatic reduction of Mg acceptor energy level, which can be as low as 30meV [11]. It will subsequently lower the resistivity of the p-type BN layer and also increase the hole concentration efficiency. These advantages are expected to enhance the EQE of the DUV LEDs. To investigate the electrical property of p-BN, we tried to fabricate ohmic contact on p-BN by different metallizatione schemes, annealing conditions, contact layers. The temperature-dependence Hall effect measurements are conducted to estimate the activation energy of acceptors of p-type GaN, with the attempt to attain similar results from p-BN. Our studies showed that the growth pressure of the InGaN contact layer plays an important role on the contact check resistance of the Au/Ni/p-BN interface.
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