Study On The Growth Of InN Films By MBE And In N-Based Heterojunction Devices In Combination With NiO

Indium nitride, as an important component part of group-III nitride semiconductor material system, has the lowest effective mass, highest electron mobility and electron drift velocity among the III-nitride semiconductors. It has been widely applied in the fields of high efficient solar cells, infrared photodetectors and terahertz devices. Especially the discovery of narrow direct band gap of InN（⁰.7e V）,has allowed the III-nitride material system to extend their spectral range from deep ultraviolet to near infrared. This will develop several new directions for the development of group-III nitride devices. However, the fabrication of the high quality InN films still has diffculty due to the lower decomposition temperature of InN films and higher equilibrium vapor pressure of N₂, which seriously hinders the development of InN materials and devices. Hence, how to prepare high quality InN films and make it available for the research on devices is the problem that needs to be solved. On the other hand, the realization of stable p-doped InN films still remains diffculty due to the highly surface electron accumulation effect of InN films, which hinders the development of InN-based optoelectronic devices. Therefore it is necessary to try to use other existing p-type semiconductor materials to combine with n-type InN films to fabricate the InN-based heterojunction devices. Nickel oxide（NiO）, as a natural p-type semiconductor material, has good chemical stability, lower resistivity and cost.It has been widely applied in the fields of transparent conductive film, UV detectors and gas sensors. Thus we propose to choose NiO as the p-type material to fabricate the InN-based heterojunction light-emitting devices in combination with InN films,which develops a new way in the research of InN-based light-emitting devices. This dissertation is based on the plasma-assisted MBE technology, mainly focus on the epitaxial growth of InN films and the fabrication of InN-based heterojunction devices in combination with NiO films. The detailed research contents are as follows:The InN films have been prepared on Al₂O₃ substrate by plasma-assistedmolecular beam epitaxy（PAMBE） system. The effects of nitridation on the physical properties of InN films have been studied. The results indicated that the InN films grown after nitridation exhibited a significant improvement in the surface morphologies, crystalline qualities and enhancement in the electrical and optical properties. The effects of temperature of In source, the flow regulating of N₂ and the epitaxial temperature on the properties of InN films has been analysed and the optimized growth conditions are obtained. When the temperature of In source is650℃, the flow rate of N₂ is 3 sccm and the growth temperature is 460℃, the InN films exhibited a two-dimensional growth mode with a smooth surface. The full width at half maximum（FWHM） of X-ray rocking curve（XRC） of the InN（0002）reflection is 540 arcsec. The photoluminescence（PL） spectrum of the InN films exhibited an obvious infrared peak and the electron mobility of InN films is519cm2/v.s. This part of research lays foundations for the application of InN films in the fabrication of heterojunction devices.The NiO films have been deposited on Al₂O₃ and Si substrate by magnetron sputtering. The effects of the sputtering temperature and the oxygen partial pressure on the properties of NiO films have been studied and the optimized growth conditions are obtained. When the sputtering temperature is 300 ℃ and the oxygen partial pressure is 40%, the NiO films exhibited good crystal qualities and electrical properties. This part of research lays foundations for the application of NiO films in the fabrication of heterojunction devices.The NiO films have been prepared on InN epilayer by PAMBE combined with magnetron sputtering. The influence of the InN epilayer on the physical properties of the NiO films has been investigated. Compare to the NiO films grown directly on GaN/Al₂O₃ substrate, the NiO films grown with InN epilayers displayed a single orientation growth with better coalescent surface and p-type conductive properties.The p-NiO/n-InN/Al₂O₃ heterojunction light-emitting device was prepared on Al₂O₃ substrate by PAMBE combined with magnetron sputtering. The results indicated that the InN films had good crystalline qualities and optical properties. The device exhibited typical rectification characteristic and the NIR emission peakedaround 1565 nm from InN layer was realized at room temperature. By comparing with the PL spectrum, the NIR emission was attributed to the band-edge recombination of the InN films.The n-InN/p-NiO/p-GaN/Al₂O₃ heterojunction light-emitting device has been prepared on GaN/Al₂O₃ substrate by PAMBE combined with magnetron sputtering.The results indicated that the InN layer grown on the NiO nano-grains exhibited a smooth and dense nanodots surface and some of the nanodots combined together to form the small islands or discontinuous films. The device revealed a typical rectification characteristic. Under forward bias, dominant near infrared emissions peaked around 1565 nm were detected at room temperature. The intensity of the NIR emission enhanced remarkably as the operating current increasing from 30 mA to 75 mA. By comparing with the PL spectrum, the NIR emission was attributed to the band-edge recombination of the InN films.The n-InN/p-NiO/p-Si heterojunction light-emitting device has been prepared on Si substrate by PAMBE combined with magnetron sputtering. The results indicated that the InN films were preferentially grown along the c-axis direction. The only one NiO related diffraction indicated a strong（200） preferred orientation and a cubic phase of Nickel oxide. The InN layer grown on the NiO grains exhibited a discontinuous film instead of InN nanodots. The device exhibited diode-like rectifying current–voltage characteristics. Under forward bias, prominent narrow NIR emissions peaked around 1565 nm were observed at room temperature. The intensity of the NIR emission enhanced remarkably with the increase of operating current. By comparing with the PL spectrum, the NIR emission was attributed to the band-edge recombination of the InN films. In addition, the stability of the LED properties was investigated in terms of the preliminary stability study of the EL performance at different driving currents and the reason for the degradation of the device characteristics was discussed.