Research On Key Technologies Of SiC-Based High-Temperature Ultraviolet Photodetector

As an important semiconductor optoelectronic device,ultraviolet（UV）photodetectors（PDs）play a key role in various fields,such as flame combustion monitoring,missile warning,geothermal monitoring,deep well detection,and aerospace energy management systems.These applications are often in extremely high-temperature environments above 400°C.At present,commercial silicon（Si）-based and gallium arsenide（Ga As）-based UV detectors are limited by their own material constraints,making it difficult for them to perform UV detection tasks in environments above 200°C alone.The accompanying filtering and cooling systems greatly increase the size and cost of the equipment.In this regard,it is urgent to seek new technologies to solve the problem of high-temperature UV detection.Silicon carbide（SiC）,as an excellent representative of third-generation semiconductors,has attracted much attention in the fields of high temperature,high power,and irradiation resistance due to its excellent characteristics such as wide confinement band,high critical electric field,and high thermal conductivity.Based on the SiC semiconductor process,this paper presents an in-depth study of high-temperature gold half-contacts,device design and development,device performance optimization,and large-scale arraying for high-temperature UV detection applications.The main research contents are as follows.（1）An n-type low-doped 4H-SiC high-temperature Ohmic contact is proposed.The novel Ohmic contact can be formed directly on the low doping concentration n-type 4H-SiC epitaxial layer(2.5×10¹⁵ cm^-3)without the extra ion implantation process.The contact metal is W/C multi-nanolayers stacked structure and comprised 5 pairs of W layer（10 nm）and C layer（5 nm）,and ten layers in total.After 1200°C annealed,the contact transformed into Ohmic contact.The test results showed that the specific contact resistance was 2.53×10^-4Ωcm² and 1.29×10^-5Ωcm² at room temperature and 500°C,respectively.The high-temperature aging results showed that it could withstand long-time high-temperature thermal storage at 500°C in the air atmosphere for 100 hours.After 100 hours of thermal storage,the specific contact resistance was 5.72×10^-5Ωcm² at room temperature（RT）and 500°C,respectively.After 100 hours of thermal storage,the specific contact resistance was 5.72×10^-4Ωcm² and 1.19×10^-4Ωcm² at RT and 500°C,respectively,without failure.（2）The potential of W/4H-SiC Schottky contact for high-temperature UV PDs was explored.It is found that the W/4H-SiC Schottky contact annealed at 1000°C increases the Schottky barrier height（SBH）from 1.21 e V to 1.61 e V.The dark current of the device is reduced from1.34×10^-11 A to 1.34×10^-13 A（about two orders of magnitude）at RT and only 1.34×10-9A（n A order of magnitude）at 400°C.（n A order of magnitude）.The PDs can operate up to400°C under 254 nm illumination（Photo-to-dark ratio,PDCR=16.1）,and improve the PDCR and responsivity,and the response time is maintained at～2 ms over the full temperature range.（3）W_xSi_yO_1-x-y interlayer technology is proposed to further enhance the limiting operating temperature of SiC-based PDs and improve the responsivity.Based on this technology,a Schottky photodiode can work up to 600℃and a metal-insulator-semiconductor-insulator-semiconductor（MISIM）UV PDs operating can work up to 550℃are realized for the first time.The novel technology inserts a 2-nm-thick W_xSi_yO_1-x-y barrier height-enhanced interlayer at the W/4H-SiC interface through the plasma pretreatment of oxygen and high-temperature annealing process.The interlayer further increases the SBH from 1.61 e V to1.96 e V.The enhanced barrier restrains the dark current deterioration in the high-temperature environment,thus increasing the limiting operating temperature.The dark current of the two PDs 1.7×10^-8A（photodiode,at 600℃）and 2.2×10^-10A（MISIM,at 550℃）,respectively.Compared with traditional SiC-based UV PDs,the novel technology solves the problem of low responsivity and quantum efficiency（QE）.Under 275 nm illumination,the responsivity of two PDs is 0.23 A/W（diode）and 0.17 A/W（MISIM）at RT,corresponding QE is about100%and 80%.In addition,W_xSi_yO_1-x-y interlayer endows two PDs with a positive dependence trend on operating temperature,and the responsivity at the highest operating temperature which is 0.52 A/W（diode,600℃）and 0.54 A/W（MISIM,550℃）.In terms of reliability,the photodiode can withstand 100 hours of high-temperature thermal storage in the 600℃air atmosphere without failure,and the MISIM structure device can withstand1000 cycles of rapid temperature shock（room temperature/550℃）in air atmosphere without failure.（4）Aβ-gallium oxide（β-Ga₂O₃）overlay technique is proposed to enhance the weak response band wavelength of SiC-based UV PDs by addressing the problem of a single response peak of SiC-based UV PDs.The technique uses magnetron sputtering and oxygen atmosphere annealing processes to grow a 120-nm-thickβ-Ga₂O₃ film on the 4H-SiC epitaxial layer.Based on this technique,photodiode and metal-semiconductor-metal（MSM）PD structures have been successfully fabricated and characterized from room temperature RT to 500℃.The novel technique enhances the responsivity at 254 nm and improves the responsivity at275 nm.The responsivity of the photodiode at 254 nm is improved from less than 0.1 A/W to 0.67 A/W at RT,corresponding to a QE of 302%.The MSM structure is even better,with3.63 A/W at RT,corresponding to a QE of 1637%.At 200°C,it is 12.91 A/W,corresponding to a QE of 5821%.The ultimate operating temperature of 1.42 A/W at 500°C corresponds to a QE of 640%.At 275 nm,the photodiode shows responsivity advantage above 200°C,and the MSM PD increases the responsivity to 1 A/W order of magnitude in the full temperature range.In terms of thermal reliability,the device has reproducible detection performance at 300°C with the introduction of aβ-Ga₂O₃ overlay.Although the detection performance of the device degrades in the high-temperature repeatability test at 500°C,the maximum operating temperature of 500°C is not affected.（5）Large-scale arraying of single-tube devices based on the key technologies of（3）and（4）.The 4×4 and 8×8 scale UV detector arrays that can operate in high-temperature environments are realized.Among them,the arrays usingβ-Ga₂O₃ overlay technology can operate up to 500°C,and the detection performance of each array point is uniformly distributed.The overall performance matches that of the single device demonstrated in work（4）.The array using the W_xSi_yO_1-x-y interlayer technique can operate up to 450°C,but the performance distribution of the array points is slightly worse.