Study On The Long Afterglow Spectra Of Aluminum Nitride Crystal By PVT

Aluminum nitride(AlN)is a direct bandgap wide bandgap(?6.02 eV)compound semiconductor,which has excellent acoustooptic and electrical properties,and has a great prospect in the field of optoelectronic devices.However,the performance of aln-based photoelectric devices and electronic devices is far from the theoretical prediction.On the one hand,the high effective doping is difficult to obtain,on the other hand,energy level distribution of defects and impurities bring much difficulty.In this paper,X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and other characterization methods were used to characterize the AlN crystal,and it was determined that the AlN crystal surface was a non-polarized m-plane,and the only impurity element in the AlN crystal was oxygen.A 266 nm laser is used to excite the sample.By setting different integration times and test temperatures to collect afterglow spectra,we systematically studied the defects and impurities that cause long afterglow luminescence in AlN crystals and the effect of temperature on the long afterglow attenuation,and discussed long afterglow luminescence mechanism.The method of segmented test is used to collect the afterglow spectrum,which is simple and effective.The afterglow time of the test is up to 5orders of magnitude,and there is some innovation in the experimental method.The main research contents and conclusions are summarized as follows:The afterglow spectra of samples excited by 266 nm laser were studied.Eight luminescence peaks,including ultraviolet light(?3.66 eV,?3.47 eV,and?3.22 eV),red light(?2.0 eV,?1.83 eV,and?1.52 eV),and blue light(?2.7 eV and?2.45 eV),were determined by the gaussian peak fitting method,which were respectively related to the aluminum vacancy-oxygen nitrogen replacement complex defect VA1-ON center and the aluminum vacancy VA1center.Blue light comes from the transition between the conduction band/valence band and theVA1 center.Ultraviolet light comes from the electron radiation transition between the conduction band and theVA1-ON center,while red light comes from the transition between theVA1-ON center and the valence band.The multipeak characteristics of ultraviolet and infrared light are related to the complexity of central structure and composition of VA1-ON.The total and partial attenuation curves of long afterglow at different temperatures at 266nm are studied.We believe that the attenuation mechanism of long afterglow at room temperature is as follows:the initial slow attenuation of ultraviolet band is due to the existence of a set of traps with short life,and the later fast attenuation is formed by the composite luminescence of(O_N)^-center,(V_Al-O_N)^1-?(V_Al-2O_N)⁰ center.The initial slow attenuation of the red band is(V_Al^2--O_N^-)^3-center and valence-band hole composite generation,and the later fast attenuation is(V^-_Al-O_N^-)^2-center and valence-band hole composite generation.The difference between the initial afterglow luminescence intensity at each temperature and the afterglow luminescence intensity at 0 ms decreases with the increase of temperature,so the attenuation rate in the early period decreases with the increase of temperature.The attenuation process of 210 K has corresponding stages with that of 17 K and 297 K.Therefore,we hypothesized that the afterglow attenuation characteristic of 210 K combines the attenuation characteristic of room temperature and low temperature.Through the irradiation of ultraviolet light on the surface of AlN crystal,the irradiation trajectory of ultraviolet light can be observed because of its long afterglow phenomenon.Therefore,the long afterglow phenomenon of aluminum nitride can be used to record the trajectory of light.