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Photoconductive Mercury Cadmium Telluride Detectors

Mercury Cadmium Telluride Short Form Catalog in PDF Format

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J15 Series Mercury Cadium Telluride Detectors

HgCdTe is a ternary semiconductor compound which exhibits a wavelength cutoff proportional to the alloy composition. The actual detector is composed of a thin layer (10 to 20 µm) of HgCdTe with metalized contact pads defining the active area. Photons with energy greater than the semiconductor band-gap energy excite electrons into the conduction band, thereby increasing the conductivity of the material. The wavelength of peak response depends on the material's band-gap energy and can easily be varied by changing the alloy composition. In order to sense the change in conductivity, a bias current or voltage is required. Typically, detectors are manufactured in a square or rectangular configuration to maintain a uniform bias current distribution throughout the active region.

Detector Bias and Operating Circuit: A basic circuit for operating J15 Series PC HgCdTe detectors is shown in Figure 2. These detectors are low impedance devices, typically 10 to 150 ohms, and require a low voltage noise preamplifier. A constant bias current is produced in the detector using a low noise DC voltage supply or battery with a current-limiting resistor RB. An AC coupling capacitor blocks the DC bias voltage from the high gain preamplifier and prevents DC saturation. For optimum performance, the model PA-101 preamp is recommended for most J15 Series detectors. The PA-101 has built-in bias circuitry and is specially matched to each detector at the factory. The PA-101's low noise, high gain and wide bandwidth insure proper performance for subsequent signal processing with oscilloscopes, A-D converters, lock-in amplifiers, etc.

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Figure 2
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D* and Responsivity vs. Bias: The responsivity and detectivity of all J15 Series HgCdTe detectors are a function of bias current. Figure 3 shows an example of relative responsivity and detectivity for a 1mm J15D14 Series LN2 cooled detector. At low bias currents, the responsivity increases nearly linearly with bias. At high bias currents, self-heating of the detector eventually causes the responsivity to fall. The point of maximum responsivity is generally not the recommended bias for the detector. System performance depends on the overall signal-to-noise ratio or detectivity. At low bias current the preamplifier noise or system noise may dominate. At high bias levels the 1/f surface noise often becomes unacceptably high. Each detector is supplied with a data sheet specifying the optimum bias current with the PA-101 preamp. The optimum bias may vary from application to application depending on background radiation levels.

Responsivity vs. Active Size: The voltage responsivity of all J15 Series HgCdTe PC detectors varies significantly with the active size of the element as shown in Fig. 4. Responsivity also depends on cutoff wavelength, field of view restriction, operating temperature and bias current. Responsivity for even "identical" detectors may range over a factor of 2 due to variations in material composition. The actual peak and blackbody responsivity data at optimum bias are supplied with each detector. As with all photon detectors, the optimum system performance is achieved with the smallest size detector capable of collecting the available incident radiation. Focusing optics are highly recommended for reducing radiation spot sizes and thereby improving signal-to-noise performance.

Figure 4
Figure 5
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Figure 4
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Figure 6

Responsivity and Noise vs. Frequency: The frequency response of HgCdTe detectors is related to the lifetime t of the electrons in the HgCdTe crystal, and t depends on material composition and operating temperature. Figure 5 is an example of responsivity and noise vs. frequency for a J15D12 Series LN2 cooled detector. The actual time constant for each detector type can be found in the specification tables. The 3dB cutoff frequency fc is given by fc = (2pt) -1. All HgCdTe PC detectors exhibit excess low frequency noise which increases approximately as f-1/2 below a certain "corner" frequency (typically 1kHz). The optimum detectivity is achieved over a wide range from the corner frequency up to the cutoff frequency fc. The actual responsivity, noise and detectivity data at 10kHz are supplied with each detector.

Figure 7
Figure 8
Figure 7
Figure 8

Linearity and Temperature Effects: Each J15 Series HgCdTe is specifically designed for a particular operating temperature range. Responsivity and detectivity will generally increase with decreasing temperature. HgCdTe PC detectors have a wide dynamic range (see Fig. 7). However, a reduction in responsivity may occur at very high incident power levels.

Applications

  • Thermal Imaging
  • CO2 Laser Detection
  • FTIR Spectroscopy
  • Missile Guidance
  • Night Vision

The J15D Series detectors are Mercury Cadmium Telluride (HgCdTe) photoconductive (PC) detectors designed for operation in the 2 to 26 µm wavelength region. The wavelength of peak response depends on the specific alloy composition used. All J15D Series detectors are designed for cryogenic operation at 77°K. Judson’s superior technology and careful device selection can provide background limited (BLIP) detectors with state-of-the-art performance.

J15D5 Series HgCdTe PC Detectors (2 to 5 µm): The J15D5 Series HgCdTe detectors peak at 5µm and are recommended for thermal imaging or infrared tracking applications which require liquid nitrogen cooled PC detectors. Excellent performance in the 3 to 5 µm wavelength region can also be obtained from the J15TE2, J15TE3 and J15TE4 Series thermoelectrically cooled HgCdTe detectors.

J15D12 Series HgCdTe PC Detectors (2 to 12 µm): The J15D12 Series HgCdTe detectors peak at 11µm with a cutoff wavelength greater than 12 µm. The devices offer optimum performance in the 8 to 12µm wavelength region with high responsivity, near-BLIP performance and fast response time. Applications include thermography, CO2 laser detection and missile guidance. Minimum and typical detectivities for all standard sizes with a 60° FOV cold stop are listed in the adjoining specification table. Cold stops for reduced FOV’s are provided for a small additional cost and may improve detectivity since detector performance is often background limited. Custom cold filters may also improve detectivity by eliminating radiation in unwanted wavelength regions. The detector is mounted in the M204 or the M205 metal dewar with ZnSe window. A wide variety of glass and metal dewar options are available, including dewars for Joule-Thomson cryostat and closed-cycle cooling. The LC1 and RC2 cooler systems allow for operation of J15D12 detectors without bulk liquid nitrogen. All Judson HgCdTe PC detectors are fully passivated and can be provided on a dewar mount or a miniature flat pack for mounting by the customer. The J15D12 Series detectors can be manufactured in a wide variety of special configurations including linear arrays, quad cells and two-color sandwich devices.

J15Dxx Series HgCdTe PC Detectors for FTIR Spectroscopy (2 to 26 µm): The J15D14, J15D16, J15D22 and J15D24 Series HgCdTe detectors are specifically designed for use in conventional or Fourier Transform Infrared (FTIR) Spectroscopy. The J15D14 series offers the highest sensitivity for "narrow band" use (750 to 5000 cm-1). The 1 mm active size is recommended for conventional sampling, and the 0.1 and 0.25 mm active sizes are best for microscope applications.

The J15D16 Series offers extended wavelength coverage for "midband" applications (600 to 5000 cm-1) while still maintaining excellent detectivity. The J15D22 Series or J15D24 Series are the detectors of choice for general "wide band" spectroscopy (425 to 5000 cm-1). They have much higher sensitivity and speed than alternative pyroelectric devices. J15D Series detectors are mounted in the standard M204 or M205 metal dewars. A variety of alternative dewars designed to fit most FTIR manufacturers’ instruments are available as options. Standard window materials for FTIR detectors are ZnSe for narrow band and midband, and KRS-5 for wide band. All windows have "wedged" surfaces to prevent unwanted interference effects. Detectivity performance data and a spectral response curve are provided with each detector.

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Literature Click for more MCT information.

J15TE Series Thermoelectrically Cooled MCT Detectors

J15TE Series "Short-Wave" detectors are photoconductive HgCdTe elements on thermoelectric coolers. They are designed for industrial and military applications that require good sensitivity in the 2 to 5 µm wavelength region without liquid nitrogen cooling. J15TE Series HgCdTe detectors offer significant advantages when compared to PbSe detectors, including high detectivity, low bias voltage, selective peak wavelength response, and fast response times.
Applications

  • Thermal Imaging
  • Industrial Process Control
  • Heat-Seeking Guidance
  • Laser Warning Receiver
  • Laser Monitoring
  • Temperature Monitoring

J15TE2 Series 2-Stage Thermoelectrically Cooled HgCdTe Detectors: J15TE2 Series detectors include a high-quality HgCdTe element, a two-stage thermoelectric cooler, and a thermistor; hermetically sealed in a TO-style package (66C, 3CN or HS1). The detector cutoff and peak response wavelengths vary depending on the selected HgCdTe material composition. Standard cutoff wavelengths for J15TE2 Series devices are 4.0 µm, 4.5 µm and 5.0 µm.

Figure 9
10Figure 8
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The 2-Stage Cooler: The two-stage thermoelectric cooler operates on low-voltage DC current to provide detector temperatures as low as –40°C (Fig. 11). The built-in thermistor can be used to monitor or control the detector temperature. Judson TE cooler power supplies and temperature controllers are recommended for convenient operation of the cooler.

J15TE3:5 Series 3-Stage Thermoelectrically Cooled HgCdTe Detectors: J15TE3:5 Series detectors include a high-quality HgCdTe element, a three-stage thermoelectric cooler, and a thermistor; hermetically sealed with dry nitrogen in the flanged, "66C" package. The detector is designed for optimum performance at 1 to 5 µm without the expense of four-stage TE or liquid nitrogen cooling.

The 3-Stage Cooler: The three-stage thermoelectric cooler operates on low-voltage DC current to provide detector temperatures as low as –65°C (Fig. 12). The built-in thermistor can be used to monitor or control the detector temperature. Judson TE cooler power supplies and temperature controllers are recommended for convenient operation of the cooler.

The 4-Stage Cooler: The four-stage thermoelectric cooler operates on low-voltage DC current to provide detector temperatures as low as –80°C (Fig. 13). The built-in thermistor can be used to monitor or control the detector temperature. Judson TE cooler power supplies and temperature controllers are recommended for convenient operation of the cooler.

Figure 11
Figure 12
Figure 11
Figure 12

Figure 13
Figure 13

Thermoelectric Cooler Operation: Figures 11, 12 and 13 show typical TE2, TE3 and TE4 cooler power requirements. The Judson CM21 assembly is recommended for optimal cooling and temperature control. The HS1 package option provides a convenient heat sink for two-stage TE cooled detectors. Heat sinks, hybrid amplifiers and temperature controllers for the TE coolers are also available.

Preamplifiers: The recommended preamplifiers for both the TE2 and TE3 Series detectors are Judson's Model PA-101 and PA-300 voltage-mode preamps. The PA-101 provides constant bias current and signal amplification for 5Hz to 1MHz operation. The PA-300 provides constant bias voltage and signal amplification for DC to 1MHz operation.


3CN Package


66S and 66Z Package

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J15TE Series "Long-Wave" detectors are photoconductive HgCdTe elements on thermoelectric coolers for CO2 laser detection at 10.6µm or for FTIR Spectroscopy The HgCdTe detectors offer significant advantages over alternative pyroelectric detectors, including low microphonics, immunity to EMI, and high detectivity over a broad range of frequencies (100Hz to 20MHz). The J15TE3:10 detectors include an economical three-stage cooler, while the J15TE4 detectors are mounted on high-performance four-stage coolers.
Applications

  • Laser Warning Receiver
  • Laser Heterodyne Detector
  • Laser Monitor
  • FTIR Spectroscopy

J15TE3:10 Series 3-Stage Thermoelectrically Cooled HgCdTe Detectors: A J15TE3:10 detector includes a high-quality HgCdTe element, a three-stage thermoelectric cooler, and a thermistor, all hermetically sealed inside the compact 66GE package. The package is flanged for convenient mounting on a heat sink. The detectors are designed for economical detection of pulsed or modulated high-power CO2 lasers.

The 3-Stage Cooler: The three-stage thermoelectric cooler operates on low-voltage DC current to provide detector temperatures as low as –60°C. The built-in thermistor can be used to monitor or control the detector temperature. The Judson CM21 cooler heat sink and temperature controller is recommended for convenient operation of the cooler.

Figure 14
Figure 14

Preamplifiers: Judson's voltage-mode preamplifiers are recommended for both the TE3 and TE4 Series detectors. The Judson preamps provide detector bias as well as signal amplification. The PA-300 preamplifier is recommended for FTIR applications and supply a constant bias voltage to the detector.

J15TE4:10 Series 4-Stage Thermoelectrically Cooled HgCdTe Detectors: A J15TE4:10 detector includes a high-quality HgCdTe element, a four-stage thermoelectric cooler and a thermistor in the 3GN hermetic package. The 3GN is a rugged package with welded seals to insure superior hermetic integrity and long life. The detectors are designed for pulsed or modulated CO2 laser applications at 10.6 µm where the highest sensitivity possible without liquid nitrogen cooling is required.

J15TE4:FTIR Series: A J15TE4:FTIR detector includes a high quality HgCdTe element a four-stage thermoelectric cooler, and a thermistor in the 3GN hermetic package. The detectors are designed to give maximum signal to noise ratios for wideband FTIR applications from 1.0 µm to the cutoff wavelength specified. In combination with the CM21 assembly and a PA-300 amplifier this series gives reliable 24 hour performance.

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The 4-Stage Cooler: The four-stage thermoelectric cooler operates on low-voltage DC current to provide detector temperatures as low as 195°K (Fig. 16). The built-in thermistor can be used to monitor or control the detector temperature. For optimum performance, the package should be mounted on a heat sink capable of dissipating 5 to 10 watts (Fig. 17). The Judson CM21 heat sink and temperature controller is recommended for convenient cooler operation.

TE4 Cooler Specifications:

- Number of Stages: 4
- Cooldown Time: 30 to 150 sec
- Min. Temp. @ 25°Ambient: -90°C
- Power Required @ 6V: 3 to 7 Watts
- Ambient Temp. Range: -55 to +60°C

66GE Package
3GN Package

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J15InSb Series MCT/InSb "Sandwich" Detectors

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Figure 18

The J15InSb Series device consists of a high quality InSb detector mounted in a "sandwich" configuration over a HgCdTe detector. The InSb detector responds to incident radiation from 1 to 5 µm while the HgCdTe detector responds to radiation from 6 to 13 µm (Fig. 18). Devices with response to longer wavelengths are also available.

The detector focal planes are spaced within 0.5 mm and their centers are aligned to within 0.15 mm. The detectors operate at 77°K and are mounted in the standard M204 or M205 metal dewar with ZnSe window. The InSb and HgCdTe elements require separate preamplifiers.

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Literature Click for more information on HgCdTe/InSb sandwich detectors.


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