| Cubic boron nitride crystal is a synthetic wide band gap semiconductor material, currently inartificial cBN was not found in nature, band-gap is 6.4eV, indirect band gap. Cut-off wavelength is 193nm. It is transparent in the visible and infrared wavelength regions and suitable for application of deep-ultraviolet detection. It has a good semiconductor properties, by doping can get P-type as well as N-type. This material has very excellent physical and chemical properties, such as: second only to diamond in hardness, good thermal conductivity, high-temperature (in the air when the temperature reaches 1200℃, It will be oxidized), anti-high-energy particle radiation and low permittivity, high breakdown voltage. It is suitable to make high-frequency device and high temperature device. And symmetry of cubic boron nitride is 43m, has zinc blende structure, two sets of face-centered cubic lattice staggered in the diagonal 1 / 4. It not has inversion symmetry and has second-order nonlinear optical effect. In optoelectronics and microelectronics, it has broad application prospects.We discussed the general working mechanism of photoelectric detectors, working principle and structure, according to the working mechanism: light emission type, photoconductivity, PV; according to the structure: PN junction, PIN junction, Metal - Semiconduct Schottky barrier type and MSM type. They each have their respective advantages and disadvantages, Light emission type require vacuum environment, the volume is big; Response time of photoconductive device is long due to persistent photoconductive effect ; PN junction, PIN junction request can not only materials P-doped but also requested materials N-doped; Characteristic of MSM PV photodetector : small dark current, short response time, fast response, simple structure and process flow and easy to integrate, because of these the MSM PV photodetector attracts people's attention . We also analyzed the physical mechanism of dark current's form. Physical mechanism includes the hot electron emission, the hole carrier drift and the hot hole emission. Physical mechanism of dark current's form under different voltage is different, according to the theory we give the formula computation. We studied characteristics of the detector under light UV and analyzed C-V characteristic; relationship between internal quantum efficiency and external quantum efficiency; the relationship between quantum efficiency, response speed and the size of the device's electrode. The many factors should be considered in designing the structure of detector's electrode, to decrease the shadow effect of the incident light.We analyzed the mechanism which cBN generates photoelectric effect, and test its optical response. Analysis that the photoelectric effect of cBN can be divided into single-photon response and two-photon response, two-photon response including multiplier and two-photon absorption, the harmonic absorption should be greater than the two-photon absorption. Therefore, we used photolithography, evaporation, stripping technology means making test samples of MSM electrode structure of cubic boron nitride. We repeated experiment and analyzed the all parameters of the process of experiment, and selected parameters of the optimal experimental. The rotate speed in order to be uniform distribution on the sample surface is 4500r/ s, pre-bake: at 80℃, 30 minutes, exposure time:2 minutes, developing and fixing time : 110s and 30s, strong film :at 120℃, 30 minutes, remove the photoresist: 80-90℃in waters for 20 minutes. Materials band gap is 6.4eV, cut-off wavelength is about 193nm, on conditional that UV irradiation for less than 193nm, cBN can occur single-photon absorption, We used a deuterium lamp as light source and tested on UV-photoelectric effect of cBN, and observed response characteristics of cubic boron nitride. Magnitude of dark current is 10- 7 A at 10V bias, photocurrent is 3, 7 times of dark current. According to analysts we used 248nm wavelength of excimer laser as the light source to test its light response. When the incident light power density is low, we did not get light response, when the incident light power density is high enough, below the high voltage we get response. With the external voltage increasing, dark current and photocurrent were also increase, The time was decreasing from the moment light on the sample to the current increased sharply, we believe it is breakdown and repetitiveness. To study deep ultraviolet detectors laid theory and experiment foundation.Since conditions for synthesis of cubic boron nitride are very strict, to make high-quality and large size of the cubic boron nitride single crystal is difficult, but the study of the fundamental nature and application of cubic boron nitride is rarely. Currently the main application of cubic boron nitride use properties of its super-hard to made abrasive, grind in the aspect of casting. However, we make cubic boron nitride sample for test, the electrode structure of the sample is MSM structure, and measured photo-electric characteristics. Application of cBN will expand into photo-electric aspect. |
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