Tiechen Zhang

High-quality heterojunction between p-type diamond single-crystal film and n-type cubic boron nitride bulk single crystal

We presented the results on the fabrication and characterization of high-quality heterojunction between p-type diamond single-crystalline film and n-type cubic boron nitride (c-BN) bulk single crystal. By employing a simple surface diffusion, we prepared the n-type c-BN bulk single crystals with relatively low resistivity (1.0×10−1 Ω cm). Combining p-type diamond films grown by chemical vapor deposition with n-type c-BN, we fabricated a high-quality heterojunction bipolar p–n diode, which the turn-on voltage of the heterojunction was 0.85 V, and the current density reached to 170 A/m2 when the forward bias was applied to 3 V.

Light emission from cBN crystal synthesized at high pressure and high temperature

The light emission at a wavelength of about 400nm is observed from the nonintentionally doped n-cubic boron nitride crystal, when the avalanche breakdown occurs inside the cBN crystal that is prepared by hexagonal boron nitride at high pressure and high temperature using nitride as catalyst. The measured spectrum has a peak in the blue-violet range. It shows the electronic transition between valleys of the conduction band of the cBN crystal. At the same time, the current-controlled differential negative resistance phenomenon occurs as well.

The influence of defects on the transport properties of AgSbPb18Te20 prepared at high pressure and high temperature

We synthesized polycrystal AgSbPb18Te20 by using the method of high pressure and high temperature, and found that the defects produced by high pressure and high temperature caused the changes of transport properties. X-ray diffraction patterns showed that the cell parameters did not change obviously with synthesis at high pressure, apart from a small fluctuation. The electrical resistivity first increased, and then decreased to one quarter of the original value, as the synthesis pressure changed from low to high. The Seebeck coefficient decreased with the increase of synthesis pressure, and then changed from positive to negative. High pressure and high temperature could cause AgSbPb18Te20 to change from a p-type to n-type semiconductor, increase the carrier concentration at maximum by two orders of magnitude, and shift the infrared absorption edge to a higher energy range. All of these phenomena were regarded as showing that high pressure and high temperature favored the formation of certain defects which could change the band structure and thereby change the transport properties.