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Study on CBN single crystal from color and shape
2020.12.16
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Cubic boron nitride (CBN) crystal is a kind of synthetic III-V semiconductor material. At present, no natural CBN crystal has been found. The results show that the band gap (~ 6.4ev) of CBN is larger than that of III-V compounds and IV group elements semiconductors, and its hardness and thermal conductivity are second only to diamond. As electronic materials and optoelectronic materials, CBN has broad application prospects, so people pay great attention to the preparation of materials, the research and application of physical properties. However, due to the harsh growth conditions, it is difficult to obtain high quality and large size CBN single crystals or thin films, which greatly limits the related research progress. In this paper, a kind of CBN single crystal with color partition (commercial model: 210) synthesized under high temperature and high pressure is studied. The eight exposed surfaces of the sample are {111} planes. The upper and lower surfaces are parallel to each other, smooth and easy to cleave. It is very suitable for the substrate material of electronic devices and optoelectronic devices. Therefore, it is necessary to study the physical and chemical properties of CBN crystal. In this paper, chemical etching, morphology observation, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and other means were used to study the surface polarity, impurities and defects of type 210 CBN single crystal samples, and some meaningful research results were obtained.

1. The research progress and difficulties of CBN synthesis and semiconductor properties are introduced, and the main research work of this paper is summarized.

2. The basic physical and chemical properties, preparation technology and some main application research of CBN are introduced.

3. The relationship between chemical corrosion, surface morphology, I-V characteristics and surface polarity of type 210 CBN crystal is mainly studied, and a convenient, fast and non-destructive method for judging the surface polarity of type 210 CBN crystal is found. The type 210 CBN crystal used in this paper is a flake sample with obvious color division, and all the exposed crystal faces are {111}. The upper and lower surfaces are parallel to each other, and the six small sides are opposite and parallel to each other. Three triangular amber regions and three triangular transparent regions are alternately and symmetrically distributed. The six triangles have a common vertex, which is located in the center of the sample. The results show that molten NaOH can corrode CBN crystal, the corrosion rate of {111} n surface is fast, the corrosion pit is triangular or hexagonal, and the size of corrosion pit is large. However, the corrosion rate of {111} B surface is slow, and the corrosion pits are triangular, and the corrosion pits are small and dense. Further observation shows that: the side connected with the transparent area is {111} B, the side connected with amber area is {111} n; the large surface with obtuse angle to the side is {111} B, and the large surface with acute angle to the side is {111} n. Therefore, the surface polarity of CBN crystals with different color zones can be determined by microscopic observation without chemical etching. After cleavage of CBN crystal along {110} surface and corrosion in molten NaOH, it is found that there are two kinds of corrosion morphology on {110} surface: one is that there is no corrosion pit and the surface is smooth and smooth. Because the corrosion rate of {110} surface is the same, there is no anisotropy, so no corrosion pits can be observed; the other is that strip-shaped corrosion pits are observed on {110} surface. The results of coplanar I-V characteristics of type 210 CBN show that the surface leakage current of n-PLANE is obviously larger than that of B-plane.

4. The impurities, defects and their chemical states in CBN crystal were analyzed by XPS. The results show that there are C, O and Si impurities in CBN crystal. The content of Si is very small, which may come from hBN raw materials. After Ar ion sputtering, the content of O impurity decreases sharply, which indicates that the o impurity originates from the adsorption and contamination of CBN crystal surface. There are still a lot of C impurities (~ 6at%) in CBN after sputtering, which indicates that in addition to some C impurities existing in the form of surface adsorption and contamination, a considerable part of C impurities exist in CBN crystal, which may come from the graphite wall of CBN crystal growth chamber. The peak fitting and chemical state analysis show that C occupies the position of nitrogen (CN) in CBN crystal and becomes the acceptor impurity. The atomic ratio of B and N is greater than 1 before and after Ar ion sputtering. The deviation of stoichiometric ratio indicates that there is n vacancy (VN) in CBN crystal, and VN belongs to donor trap. Vn-cn can form donor acceptor pairs, which not only affect the electrical properties of CBN, but also affect the luminescent properties of CBN crystal, making the luminescence spectrum of CBN complex. Further study shows that the XPS spectrum is also affected by the surface polarity of CBN crystal. Before sputtering, the B: N ratio of N side is lower than that of B side; after sputtering, B: N ratio of B side decreases, but B: N ratio of N side increases. From the fitting results of C1s spectrum before sputtering, it can be seen that there may be c-n-b bond on N side, or there are many defects on N side; c-b-n bond may exist on B side.

5. Raman spectra of type 210 CBN single crystal were studied. The results show that Raman of CBN crystal is also related to the polarity of B and N faces. For the (111) B plane, only to mode (1053cm ~ (- 1)) and lo mode (1305cm ~ (- 1) 53cm ~ (- 1)) were observed, and the opposite side was observed at the peak. In the n-PLANE, the sources of the edge peaks are analyzed from the following five aspects: the interaction between the two modes is 5C, m-1955cm ~ (- 1), 12 local modes, boron rich, WBN and disorder induced Raman scattering (DARS). There are many defects in the {111} n plane, so the phonons far away from the center of Brillouin zone may also scatter, leading to the appearance of edge peaks. 925cm~(-1)


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