They are based on earlier ‘quantum well infrared photodetectors’ (QWIPs) that are flying on Landsat 8, and will be flying Landsat 9, which monitor vegetation from space.
SLS imaging arrays are fabricated on a semiconductor wafer, using hundreds of alternating epitaxially layers tuned to absorb infrared photons and convert them into electrons, according to NASA. A read-out chip is directly mated to the array.
SLS detectors are 10x more sensitive than QWIMPs, operate over a broader spectral range and, importantly operate at 70K instead of 42K for QWIPs.

Resolution of SLS detector array (right) compared warlier QWIP

It consumes little power, operates at liquid-nitrogen temperatures, is easily fabricated, and is inexpensive “almost to the point of being disposable,” said NASA detector engineer Murzy Jhabvala of the Goddard Space Flight Center, who worked with New Hampshire-based QmagiQ to create a practical SLS detector assembly – shown – which is ~400mm long and 150mm high.