cBN is one typical compound and has zinc-blendestructure.Due to several unique properties including large band gap upto 6.3eV and steady chemistry properties ,cBN is regarded as the idealmaterial that will be made to high-power shortwave devices which canwork at high temperature. Therefore , cBN attracts much attention for itspotential application to semiconductor and optical devices.It is insulated for pure cBN single crystal and we can gained p-andn-type crystals using two kinds of ways. Appropriate impurities such asSi or Be is added into the material when cBN is synthesized. Diffusingmethod is the other way .After cBN is synthesized under high pressureand high temperature,it becomes doped as a result of impuritiesdiffusing under high temperature and vacuum.All the properties of cBNis unique among the materials with wide band gap and that makes itpossible to fabricate p-n junctions and ultraviolet-light-emitting diodes.Mishima made p-n junction when they grew n-type cBN crystals onp-type in 1990’s and enhanced the temperature to 650℃at which theI-V characteristic curve of p-n junction was kept well.Their work showedthat the study on cBN semiconductor had entered into a new phasefrom then on.However,the fundamental study of the semiconductor properties ofcBN has not largely progressed for many years, probably due to thelack of large-scale single crystals of high quality because of thesynthesis technology. Technical difficulties associated with the processof obtaining p-n junction crystals under high pressure may have alsoprevented further investigation of the ultraviolet-light-emitting nature ofcBN crystals. Recently, we have studied the semiconductor propertiesof cBN single crystals contained no intentional dopants and synthesizedunder high pressure and high temperature, and acquired some betteradvancement.we analyzed absorption spectrum of cBN in order to analyzing itsenergy gap and impurity level. UV WINLAB spectral analysisappearance was used for this experimentation. The process ofanalyzing was controlled by computer. The result of data was calculatedby MOLECULAR SPECTROSCOPY. We analyzed that the cBN intrinsicabsorption long wave bounds was 198nm. We calculated the energygap of cBN was 6.3ev by virtue of the formula:λ=1.24/Eg(ev)(μm).Itequals the energy gap of cBN that we adopted.There have many viewpoints about the energy gap of cBN. Wecalculated the energy gap of cBN by a new computer simulation in orderto analyze its character. The theory of calculation is used by thequantum mechanics of CASETP in the commercialization softwarepackage of Cerius2 in the Co. Accerlrys in the United States. The theoryof CASTEP is based by Local Density Approximation or GradientCorrected LDA.The crystal parameter of cBN was input the quantum mechanics ofCASETP in order to construct the crystal parameter model of cBN. Wecalculated the energy gap of cBN by the method of Gradient CorrectedLDA. The method underestimates the value of nonconductor about 1 to2ev. We got some opinions as follows: cBN is indirect bandsemiconductor. The energy gap of cBN is 4.76ev. The true energy gapof cBN was 6.26ev based of the feature of GGA. It equals to the energygap educed by the third chapter. Ultraviolet light detector can be produced by the intrinsicphotoelectric effect of cBN. cBN has wide band. Ultraviolet light detectorproduced by cBN isn’t sensitive to visible light and infrared light, but issensitive to ultraviolet light that is small than 197nm. This is veryimportant to detecting ultraviolet light in the background of visible lightand infrared light. So, the study of ultraviolet light of cBN is veryimportant. We introduced some experiments and analyzing of theintrinsic photo-electronic conductance of cBN. PL. amplifier couldn’tobserve the change of cBN. The cause is as follows: 1) the cause of illuminantThe light of xenon lamp was spectrum by monochrome appearance anddecomposed to the homogeneous light from 200nm to 600nm.