| Ultraviolet detection technology has a wide range of application scenarios in the military and civilian fields.Among the many semiconductor materials used in the production of ultraviolet detectors,the emerging third-generation semiconductor material 4H-SiC has a wide band-gap and many advantages such as high critical electric field,higher thermal conductivity,and higher anti-irradiation.At present,SiC UV detectors mainly have various device structures such as PIN diodes,APD avalanche detectors,MSM UV detectors and Schottky UV detectors.Compared with other structural devices,the BJT structure detector can obtain a larger internal gain at a lower bias voltage with simple manufacturing process and low internal noise.This article mainly discusses the mechanism of the BJT structure 4H-SiC ultraviolet phototransistor,simulates the BJT structure of the new type punch-through transistor,and studies the influence of the device structure parameters on the photoelectric characteristics.In addition,the corresponding surface micro-etching method is used to improve the responsivity of the detector.The main research methods and research results are as follows:Firstly,the characteristics of the new punch-through structure SiC ultraviolet phototransistor are simulated.Through the controlled variable method,the various parameters of the device are designed,and the optimized parameter values of the punch-through transistor are determined as follows:The thickness of the n-type collector region in the narrow base region is 0.7?m,and the doping concentration is 1×1019cm-3.The thickness of the p-type base region is 0.6?m,the doping concentration is 1×1016cm-3.The thickness of the n-type emitter is 0.7?m,and the doping concentration is 1×1019cm-3.The thickness of the n-type collector region in the wide base region is 0.1?m,the doping concentration is 1×1019 cm-3.The p-type base region thickness is 1.8?m,the doping concentration is 1×1016 cm-3.The n-type emitter region thickness is 0.1?m,and the doping concentration is 1×1019 cm-3.Under this parameter value,the order of magnitude of the photocurrent reaches 10-5,while the ratio of light to dark current is an order of magnitude.Secondly,this article also conducts experimental research on changing the surface morphology of the device to improve the response of the device,designing the process flow of the UV phototransistor of the BJT structure,using the L-Edit software to design and draw the layout,and finally carry out the tape test.Through the device IV characteristic test,the photo-dark current ratio of the device after surface microetching can reach four to five orders of magnitude.The linearity is better under different areas and different optical power densities,and the response speed of the device is also faster.The rise time is about 180m,and the fall time is about 50ms.The same device of different units has good consistency.At the same time,due to surface micro-etching,the reflection path of ultraviolet light on the surface of the device can be changed,and the light absorption rate of the device is improved.Take a square device described in this article as an example.When irradiated with an ultraviolet wavelength of 254 nm,the surface is not micro-etched.The photocurrent density during etching is 2.32×10-2A/m2,after surface microetching,the photocurrent density is3.11×10-2A/m2,the value of the photocurrent is increased by 31.4%,and the ratio of light to dark current is increased by 31%.When irradiated with 365nm ultraviolet wavelength,the photocurrent density is 7.85×10-4A/m2 without surface microetching,and the photocurrent density is 1.23×10-3A/m2 after surface microetching,and the photocurrent value is increased by 56.6 The ratio of light to dark current has also increased by 56.6%. |
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