HgCdTe (photoconductive) 2 - 26 µm
HgCdTe is a ternary semiconductor material. Its composition determines the cut-off wavelength.
HgCdTe Detectors
HgCdTe is a ternary semiconductor material. Depending on its composition the cut-off wavelength can be shifted.
Materials
The real detector is made of a thin HgCdTe layer (ca. 10 to 20 µm) with metalized contact surfaces limiting the active area.
Photons with energy greater than the bandwidth of the forbidden zone (bandgap) of the semiconductor (band model) excite electrons. The electrons then jump to the conduction band and in doing so increase the conductivity of the detector material.
The peak wavelength of the detector depends on the width of the forbidden zone and can be changed by altering the composition. To realize the change in conductivity a bias current or bias voltage is required.
Typical manufacturing shapes of detectors are square or rectangular. This enables a uniform field distribution.
Sensitivity and Detectivity of the J15 Series
Both the sensitivity and detectivity (D*) of all of the J15 (HgCdTe) series detectors depend on the bias current. At low bias currents the sensitivity increases almost in a linear fashion equal to that of the bias voltage. Normally, the bias voltage range, in which maximum sensitivity is reached, is not the recommended value for the bias voltage.
The working principle of the system (detector + electronics) depends on the total SNR. At low bias currents either the preamplifier noise or the system noise can dominate. At very high bias voltage levels the 1/f surface noise often becomes unacceptably high.
Quality Check
Prior to shipping, each individual detector is measured by the manufacturer and delivered with a datasheet, on which the optimal bias current, the PA-101 preamplifier, and other information is stated.
