Study On Residual Compressive Stress Accumulated In BN Films And The Preliminary Exploration About Ultraviolet Photoresponse

Cubic boron nitride (cBN) films have the tempting and potential applications in mechanics, electrical devices and optical devices,etc.,because cBN thin films own many excellent properties, for example large band gap (6.4eV), high puncture electric field strength, sensitive ultraviolet responsivity, more easily to implement p-style or n-style doping and impossible to react with ferrious materials below1373K compared with diamond films. But the premise for the applications is preparation of high quality cBN films. So far, it’s well known that ion bombardment of the BN films is necessary requirement regardless of physical vapor deposition preparation technology or chemical vapor deposition preparation technology. Unluckily the ion bombardment is inevitably accompanied with strong residual stress which results in the delamination of the cBN films. Moreover, the clear understanding of the process of the formation of residual compressive stress is essential to study the mechanism of the nucleation and growth of cBN thin films.So the study of residual compressive stress is very impotant.The origin of the residual compressive stress in cBN films and the interaction of infrared-absorption with the residual compressive stress, besides the ultraviolet photoresponse of the cBN-based detector have been investigated.(1) A more accurate method was proposed to evaluate residual stress. The computational results by the first-principles density-functional theory with local density approximation and the experimental results show: the infrared-absorption peak of the B-N bending mode (around780cm-1) belonging to hexagonal boron nitride (hBN) will shift at the rate of-3.45cm-1/GPa with increasing compressive stress. Evaluating residual compressive stress is more accurate by the infrared absorption peak shifts of B-N bending mode compared with the infrared absorption peak shifts of cBN(around1080cm-1).(2) The probable reason for residual compressive stress was discussed thoroughly. The formula derivations and the experimental results suggest:the interstitial Ar atoms in cBN films result in strong residual compressive stress and the decline of the total degree of the freedom in ordered regions which suppress the infrared-absorption of cBN crystal.So the phenomenon that the infrared-absorption peak intensity of cBN with the residual compressive stress changes was explained reasonably in our experiment.(3) The preliminary research on ultraviolet photoresponse:A simple ultraviolet detector based on S-doped cBN films was fabricated. The curve of current-voltage and the ultraviolet light photoresponse of the cBN-based detector was measured. The experimental data and the figures find that the ultraviolet light located in around254nm creates the maximal photoresponse, which demonstrates the tempting prospects in solar-blind ultraviolet photoresponse filed.(4) Preparation of cBN films was implemented by the plasma enhanced chemical vapor deposition(PECVD) equipment set up by ourselves.The relationship between the experiment parameters and the results was discussed and the cubic phase content more than80%of cBN films have been prepared successfully.