Image sensor for time-of-flight system and methods of making the same

A Time-of-Flight imaging system, comprising:

• an illumination unit configured to emit light signals;
• an image sensor that detects the light signals from the illumination unit that are reflected from one or more objects in a field-of-view of the image sensor and are received at the image sensor;
• and
• a processor configured to determine distance information for the one or more objects based on the light signals detected at the image sensor, wherein:
• the image sensor comprises an array of sensor elements, each sensor element including a photodetector and a sensing circuit, and the array includes a plurality of primary sensor elements and at least one secondary sensor element, where each primary sensor element includes a photodetector that includes a photovoltaic junction formed at least partially in a germanium-containing material that includes germanium at an atomic percentage greater than 50%, and each secondary sensor element includes a photodetector that includes a photovoltaic junction formed in a second material that includes germanium at an atomic percentage between 0% and 50%.