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J12 Series
detectors are high-quality Indium Arsenide photodiodes for use in the 1
to 3.8 µm wavelength range. The equivalent circuit is a
photon-generated current source Iph with parallel capacitance Cd, shunt
resistance Rd, and series resistance Rs (Fig. 1). The output signal
current Is is defined as:
Is = Iph Rd/Rd + Rs + Rload
Rd varies as a function of detector
temperature (Fig. 2). Rs depends on the position of the source light
spot on the detector surface; it varies with the distance from the spot
to the detector contact ring . When Rs is small compared to Rd it may be
disregarded, but with room temperature InAs the effects of Rs are
significant.
Figure 1  Figure
2
Responsivity
The effect of Rs on the apparent response of an InAs detector is illustrated below. At 22°C, Rs and Rd may have the same order
of magnitude (~10 ohms). As a result, although incident photons generate carriers uniformly over the detector area, some of the carriers
generated near the center of the area may be "shunted away" through Rd and fail to reach the contact ring. This results in a "dip" in response at
the center of the detector's active area (Fig. 3). The effect is less pronounced in small-area detectors, which have higher Rd and less surface
area. The effect is also reduced or eliminated by cooling the diode, thereby increasing the detector Rd.
 
Figure
3
Temperature Effects: Cooling an InAs photodiode reduces noise and improves detectivity (Fig.
4). Cooling also increases shunt resistance
Rd as described in the previous section, allowing more of the photocurrent Iph to reach the contact ring. The result is an increase in the diode
response (Fig. 3). For high-power applications such as pulsed laser detection, cooling is generally not necessary. For sensitive, low-power
applications such as temperature measurements, the InAs detector should be cooled or at least temperature-stabilized. Stabilizing the
temperature near 22°C room temperature will not improve performance, but will prevent changes in detector response due to ambient temperature
drift.
 Figure
4 
Figure 5
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Applications
Laser Warning Receivers Process Control Monitors Temperature Sensors Pulsed Laser Monitors Infrared Spectroscopy Power Meters
Thermoelectric Cooler Operation: Figure
6 shows typical power requirements for the TE1, TE2 and TE3 coolers. The built-in thermistor can be
used to monitor or control the temperature. Figure 7 shows typical thermistor resistance vs. temperature values. Sensitivity, cutoff
wavelength and response uniformity are all functions of temperature. Detector temperature should be optimized for a particular
application.
Figure 6 
Figure 7
Detector Shunt
Impedance |
Recommended
Cooler Module |
Part Number |
<
400 ohms |
CMAMP-TO66-PA5
CMAMP-3CN-PA5 |
490130
490132 |
400
ohms to 50Kohms |
CMAMP-TO66-PA6
CMAMP-3CN-PA6 |
490146
----- |
>
25Kohms |
CMAMP-TO66-PA7
CMAMP-3CN-PA7 |
490139
490141 |
CMAMP assembly includes heat sink, temperature controller and transimpedance
amplifier for the J12TE packages. |
Operating Circuit
The recommended operating circuit for most applications is an operational amplifier in a negative-feedback transimpedance
configuration (Fig. 8). The feedback circuit converts the detector output current to a voltage, while the op-amp maintains the detector near
zero-volt bias for lowest noise. Because RD varies significantly with temperature, selection of the proper op-amp will depend on the detector
operating temperature as well as the desired bandwidth. The feedback resistor RF should be at least 10x greater than RD for best signal-to-noise
ratio. Judson has preamplifiers for optimum performance with each detector type. For high frequency applications, the detector may be reverse
biased and terminated into a low impedance load (Fig. 9). Maximum reverse bias is 1 volt.
 Figure
8
Figure 9
Advantages of InAs
Unlike the photoconductors commonly used in the 1-3.8 µm wavelength region, InAs operates in the photovoltaic mode
and does not require a bias current for operation. This makes InAs the better choice for DC and low-frequency applications, as it does not
exhibit the low-frequency or "1/f" noise characteristic of the photoconductors PbS, PbSe, and HgCdTe (Fig.
10). InAs also offers superior
pulse response for applications in monitoring and detecting high-speed pulsed lasers.
Figure 10
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Models
The J12 Series Indium Arsenide (InAs) detectors are photovoltaic infrared photodiodes sensitive in the 1.0 to 3.8 µm wavelength region. Diode
sensitivity, speed of response, impedance and peak wavelength can be optimized by operation at the proper temperature. Judson offers a variety
of convenient packages for room temperature and thermoelectrically cooled operation. Linear arrays, X-Y position sensors and special
configurations are also available.
J12 Series Room Temperature InAs Detectors: These photodiodes operate at ambient temperatures and are excellent for wide bandwidth (DC to
16MHz) applications such as infrared laser monitors and fast temperature sensors. The devices are available in 0.25 mm, 1 mm or 2 mm diameter
active sizes and are mounted in the 18C, 5AP or convenient LD2 BNC connector packages. For low frequency applications (DC to 50KHz) the
Model PA-5 transimpedance gain preamplifier is strongly recommended. The PA-5 has extremely low voltage noise, low offset voltage and
adjustable gain for the best possible match to these low shunt resistance detectors. For high speed applications, the Model PA-101 (5Hz to
1MHz) preamplifier can be used. InAs detectors can be reverse-biased to reduce junction capacitance
and improve frequency response.
Click for more InAs information.
Thermoelectrically
Cooled Indium Arsenide
J12TE1 Series 1-Stage Thermoelectrically Cooled InAs: The J12TE1 Series detectors are high quality temperature stabilized InAs detectors
mounted on a one stage thermoelectric cooler. The TE1 series was developed for applications such as temperature monitoring, power meters and
infrared spectroscopy where low cost, responsivity, stability and low noise are important issues.
J12TE2 Series 2-Stage Thermoelectrically Cooled InAs: The J12TE2 Series detectors are high quality InAs photodiodes mounted with
thermistors on two-stage thermoelectric coolers and hermetically sealed package. The 8B6 package is standard, with the 66S or HS1 packages
available as options. At the standard operating temperature of -40°C, the J12TE2 Series detectors have a much higher shunt resistance than
room temperature detectors, resulting in higher responsivity, lower noise and better stability for DC or chopped light applications. See Figs.
6 and 7 for thermoelectric cooler operating information.
J12TE3 Series 3-Stage Thermoelectrically Cooled InAs: The J12TE3 Series detectors are high quality InAs photodiodes mounted in the 66S
package which includes a built-in thermistor, three stage thermoelectric cooler and hermetically sealed package. J12TE3 devices are ideal for
critical military, space or industrial applications requiring high detectivity, good uniformity of response and wide bandwidth.
J12TE4 Series 4-Stage Thermoelectrically Cooled InAs: The J12TE4 Series detectors are high quality InAs photodiodes mounted in the 3CN
package which includes a built-in thermistor, four stage thermoelectric cooler and hermetically sealed package.
Click for more TE Cooled InAs information.
View Model Number Table
18C Package
5AP Package
37S Package
66D Package
3CN Package
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