pn Junction type CdTe
CdTe radiation detector is direct conversion type semiconductor having Ws value of 4.43eV and higher stopping power due to high mass densities of its components.
Semiconductor detectors i.e. Ge(Li), Si(Li), and (HPGE) are in use for long time in sophisticated research facilities and applications; however, they are expensive to produce and use; Furthermore, these detectors require cooling and/or complex setups.
CMOS has been redefining pinnacle of advancement in optical imaging technology since long. Although CMOS sensors are best for low energy photons(optical range), they are being utilized for detecting higher energy(X-ray) photons in conjunction with scintillator materials, which are denser and capable of absorbing shorter wavelength electro-magnetic waves and convert them into visible range energy photons that can subsequently be detected by CMOS sensors. The two-step conversion method i.e. Photon to Photon to Electrons, emanates other complexities and limitations in the imaging systems; and concludes to loss of energy information contained in incident photons.
CdTe detector directly converts X-ray photons to electric signals and thus eliminates false detection of scattered visible light photons, reduces the point spread, and results in better modular transfer for any X-ray imaging system. Direct conversion of X-ray photons happens at the CdTe junction in an individual pixel unit, the stopping of high energy photon and conversion to electrical charge occurs and sensors pixels in proportion to incident photon energy. This enables imaging system to achieve high sensitivity and greater resolution, when compared to conventional scintillator systems.
Laser doping technique for pn junction
As compared to Silicon, Cadmium Telluride detector material is extremely difficult to process and make it a X-ray sensor. With conventional CdTe detectors, junctions can only be made at the electrode interface, and the characteristics of semiconductor light-conversion elements have not been entirely utilized.
An advanced semiconductor process developed at Shizuoka University that utilizes laser-based doping enabled us to achieve required embedded bond.As a result, we have succeeded in manufacturing a higher-performance CdTe detector, and have a great advantage in X-ray sensors that make full use of the characteristics of CdTe.