Diamond surface water vapor annealing leads a new generation of power devices

Diamonds are often shown as gorgeous jewelry displays. But this solid carbon is also known for its excellent physical and electronic properties. In Japan, researchers at the Graduate School of Natural Science and Technology of Kanazawa University and the Industrial Technology Research Institute of Tsukuba, led by Kyo Yoshida, used steam annealing to form an atomic-level flat hydroxyl-terminated diamond surface.

Diamond has many outstanding features, making it a good application prospect in electronic equipment. However, the defects contained in diamond are observable at the atomic level, and these defects produce unique surface characteristics that affect the use of diamond in such devices. The surface termination using oxygen or hydrogen stabilizes the diamond structure. The hydrogen-end diamond surface contains a two-dimensional hole gas layer (2DHG) for high temperature and high pressure operation. The oxygen-end diamond surface is formed by surface oxidation of the hydrogen end surface, which removes hydrocarbon (CH) bonds and 2DHG, "but this can make the diamond surface rough and cause device performance degradation," Norie Tokuda, Kanazawa University, Japan Speaking of it.

To solve this problem, the researchers used a steam annealing method. They proceeded from high-pressure, high-temperature synthesis of (111) crystals to single-crystal diamond Ib and IIa substrates. A homoepitaxial diamond film was prepared on an Ib substrate by microwave plasma chemical vapor deposition (MPCVD). To obtain an atomically flat hydrogen end surface, the diamond sample is exposed to a hydrogen plasma in an MPCVD chamber. To form a hydroxyl terminated surface, a diamond sample at the hydrogen end is subjected to a water vapor annealing treatment.

The results show that the carbon-hydrogen bond remains on the diamond surface during the steam annealing process below 400 ° C; therefore, a two-dimensional hole gas layer is detected. “However, water vapor annealing above 500°C removes the carbon-hydrogen bonds on the diamond surface,” explains Yoshida. “This indicates that the two-dimensional hole gas layer (2DHG) has disappeared.” Therefore, water vapor annealing can remove 2DHG, At the same time, the surface morphology of the (111) oriented diamond surface is maintained. "Compared to conventional techniques for removing 2DHG, such as wet chemical oxidation," Tokuda said, "water vapor annealing has the advantage of maintaining an atomic-level flat surface."

Diamond is one of the special materials in nature, with the highest hardness, low friction coefficient, high elastic modulus, high thermal conductivity, high insulation, wide energy gap, high acoustic propagation rate and good chemical stability, as shown in the following table. Although natural diamonds have these unique properties, they have always existed only in the form of gemstones, and their versatility and rarity greatly limit their applications. The CVD diamond film prepared by Luoyang Yuxin Diamond combines these excellent physical and chemical properties, and the cost is lower than that of natural diamond. It can prepare various geometric shapes and has broad application prospects in the fields of electronics, optics and machinery.

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