Epitaxial Growth and Characterization of Balgainn Hetrostructures(2/3)

Technology advancement of III-nitride semiconductors has been very impressive in the last 20 years as evidenced by its wide adoption in consumer products as well as equipment in information and communication technology sector. Among the III-nitrides, boron nitride (BN) is a material with several merits for future applications. For instance, h-BN has bandgap as large as 6 eV, it has an exciton binding energy as high as 130 meV. The acceptor activation energy of Mg in h-BN is reported to be as small as 30 meV with a small hole effective mass. This means h-BN has a high breakdown field and can be a much more conductive p-type semiconductor than its AlN counterpart. These are very essential for applications in deep ultra-violet light emitting diodes and high power devices. Given the aforementioned advantages of h-BN, it would be even more desirable if BN could be combined with more well-developed GaN-based materials to form alloys and heterostructures so that a greater flexibility of material design is offered to pave the way to more innovative applications. While all the positive aspects predicted theoretically for B containing nitrides, none of them have been realized so far. This is basically due to the limited advancement of material preparation technology. Without high quality materials, the material parameters used for predicting all these positive potentials might also be in question. It is obvious that epitaxial growth technology must be greatly improved to realize these potentials. As the development of BAlGaInN material is still in its infant stage globally and no such activity is found in Taiwan, a three-year plan is proposed to develop metal-organic chemical vapor deposition (MOCVD) epitaxy technology of this novel material and systematically investigate its fundamental properties. The first year will be focused on the growth BGaN and BAlN ternary compounds and investigation of their fundamental properties; the second year will be devoted to the growth of BAlGaInN heterostructures to investigate the dependence of B content on spontaneous polarization constant and their energy band offsets; and the their year will be used to explore the possibilities of applying these B-containing materials to GaN-based high electron mobility transistors (HEMTs) as a buffer layer, barrier layer as well as a passivation layer. This work is expected to enrich the data base of this material system and open a new area of research.