The camera sensor of the new iPhone SE is similar to that of the iPhone 8. This is apparent from a teardown from iFixit. The iPhone SE and iPhone 8 camera modules are interchangeable, as are a number of other components.
Judging by the specs Apple released, it looked like the iPhone SE would include the camera sensor from the iPhone 8 or from the iPhone XR. iFixit’s teardown removes any doubt about that; the camera module that Apple puts in the iPhone SE is identical in size to that of the iPhone 8. The camera sensor used in that module is slightly smaller than that of the iPhone XR and other newer iPhones, as can be seen in photos from iFixit.
From left to right: camera module of iPhone SE, iPhone 8, iPhone XR
The photo quality of the iPhone SE can be improved compared to the iPhone 8, because of better image processing with the A13 Bionic-soc. At the announcement it already appeared that the new iPhone SE does not have support for the night mode, which is on all other new iPhones. This may have to do with the sensor used.
IFixit has made an overview of the parts that are interchangeable between the iPhone 8 and the new iPhone SE. In addition to the camera module, the simtray, Taptic Engine and the full screen module including microphone and proximity sensor are also interchangeable. Differences are in the housing; the iPhone SE has different antennas for faster 4g speeds and Wi-Fi 6 support. The battery also has a different connection, so it is not interchangeable.