Which solid-state detector technology was developed first?

• A. CCD
• B. CMOS
• C. APD
• D. SPAD

Answer: (A)

The question tests understanding of the historical sequence of solid-state imaging detectors. The charge-coupled device was developed first, introduced in 1969 by Willard Boyle and George Smith. A CCD captures light as charge in an array of pixels and then transfers that charge across the chip to a readout node, enabling the first practical digital images with relatively simple and scalable architecture. This early approach set the standard for imaging sensors for many years. CMOS image sensors, which integrate pixel structures and readout circuitry on a single chip and later offered advantages in cost and integration, came later. Avalanche-based detectors like APD and SPAD exist as fast photodetectors and photon-counting devices rather than primary imaging sensors, and their development followed CCDs in the imaging context. So, the earliest solid-state imaging detector among these is the CCD.