JPS62163939A - Evaluation method for infrared detector - Google Patents

Abstract

PURPOSE:To enable comparison between a theoretical value and a measured data, by measuring sensitivity after a rise in the temperature of a detector itself caused by heat due to a bias current is offset. CONSTITUTION:In the evaluation of sensitivity of a photoconductive type infrared detector with a large heat generation by a bias current, a means for adjusting the temperature of a detector holder is provided and the maximum of an output is read from a data obtained with the output of the detector at a several bias current values as function of temperature of a detector holder and are plotted as functions of bias currents to correct the effect of the heat generation. In other words, in order to correct the effect of the heat generation, it is necessary to offset a rise in the temperature of the detector itself by setting the temperature of the detector holder at a low temperature. The responsivity as obtained when the temperature of the detector holder is lowered step by step reaches the maximum at a certain temperature. This measurement is conducted for several bias currents and the maximums of the response are plotted with respect to the bias currents to obtain a data for the dependence of response on bias current with a corrected effect of the heat generation.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for determining the correct sensitivity by correcting deterioration in sensitivity due to heat generation in evaluating the sensitivity of a photoconductive infrared detector that generates a large amount of heat due to bias current. It is something.

(Prior Art) When measuring the bias current dependence of the sensitivity of a HgCdTe photoconductive infrared detector, the temperature of the detector holder was fixed at, for example, the liquid nitrogen temperature of 77 K (FIG. 4). In the figure, infrared radiation from a blackbody furnace 1 is converted into alternating current by a chopper 2 and is incident on a detector 4 attached to a detector holder 5 in a dewar 3.

6 is a single deyuwa. The quantity detector holder is cooled by a liquid nitrogen reservoir 7, and its temperature can be determined by a temperature measuring resistor and a temperature measuring device 11 attached to the holder.

The output of the detector is amplified by a preamplifier 9 and then input to a spectrum analyzer 10. It has been known for some time that when the evaluation device shown in the figure is used, the temperature of the detector itself increases due to the heat generated by the bias current, and the sensitivity decreases (C.T. Elliot
tt) etc. Infrared Physics (Infrared
Physics) Vol. 22 (1982, p. 31).

(Problems to be Solved by the Invention) According to the conventional evaluation method for HgCdTe photoconductive infrared detectors, when the temperature of the detector holder is kept constant, the susceptibility decreases when a bias current larger than a certain value is applied. The details are as follows. HgCdT
The e-detector is bonded to an insulating substrate such as sapphire with an epoxy adhesive. Adhesive thickness is 311m
At low thermal conductivity, large bias currents are required due to the low thermal conductivity.

In the case of a HgCdTe detector, the temperature of the detector itself increases due to Joule heat. If the dependence of the responsivity of the detector on the bias current is plotted under this situation, the result will be as shown in FIG. As can be seen from the figure, when the temperature of the detector holder is kept constant, the responsivity decreases when the bias current exceeds a certain value. The main cause of this is heat generated by bias current. This makes it very difficult to compare the performance of the detector with the theoretical value, which means that it is not easy to find a correspondence between the various quantities that determine performance that should be improved to improve performance. The purpose of the present invention is to provide a method that offsets the temperature rise of the detector itself due to heat generated by bias current, measures sensitivity, provides data corrected for the effects of heat generation, and facilitates comparison with theoretical values. It's about doing.

(Means for Solving the Problems) The present invention includes a means for adjusting the temperature of a detector holder in evaluating the sensitivity of a photoconductive infrared detector that generates a large amount of heat due to bias current, and detects detection at several bias current values. The present invention is characterized in that the maximum value of the output is read from data obtained as a function of the temperature of the detector holder and the maximum value of the output is plotted as a function of the bias current to correct for the effect of heat generation.

(Function) In order to correct the effect of heat generation mentioned above, it is necessary to offset the temperature rise of the detector itself by lowering the temperature of the detector holder. When the temperature of the detector holder is lowered, the responsiveness reaches a maximum value at a certain temperature.

By performing this measurement for several bias currents and plotting the maximum value of responsivity against the bias current, it is possible to obtain data on the bias current dependence of responsivity that has been corrected for the effects of heat generation. can. By correcting the effects of heat generation in this way, it becomes possible to compare theoretical values and measured data, and it is also possible to find correspondences that determine which variables that determine performance should be improved to improve performance. .

(Example) Figures 1 to 3 show examples of the present invention. The photoconductive infrared detector 4 is an n-type Hg0.795CdO, 205T.
An integral type crystal, commonly called SPRITE, was used, which was made by thinning a single crystal of E to a thickness of 13 pm and attaching a Cr--Au electrode. The dimensions of the device are as follows: the length of the drift region is 700 pm, the width of the same region is 65 pm, the length of the read region is 6011 m, and the width of the same region is 40 pm. This element is attached to a sapphire substrate with a thickness of 0.5 mm using an epoxy adhesive. The thickness of the adhesive is 4.511m
Met.

FIG. 1 shows an apparatus for evaluating the sensitivity of an infrared detector. Infrared radiation from the blackbody furnace 1 is converted into alternating current by a chopper 2 and is incident on a detector 4 attached to a detector holder 5 in a dewar 3. The output of the detector is amplified by a preamplifier 9 and input to a spectrum analyzer 10. A resistance temperature detector is attached to the detector holder 5, and the temperature is displayed on the temperature detector 11. Further, by reducing the pressure in the liquid nitrogen reservoir 7 using the pressure reducing device 8, the temperature of the detector holder 5 can be lowered. As shown in the figure, a diaphragm 12 with an aperture ratio of 16°7 and a narrow band interference filter 13 (center wavelength 10.9 pm, wavelength width 0.75
pm, transmittance 75%) and was placed in a Dewar-3 and cooled to liquid nitrogen temperature. The liquid nitrogen reservoir 7 is depressurized by a pressure reducing device 8 consisting of a rotary pump, a needle valve, and a Bourdon tube, and is cooled to a solid nitrogen temperature of about 50K. The temperature was measured by connecting a Pt-Co resistance temperature detector attached to the detector holder 5 to the temperature meter 11. The temperature meter consists of a 1 mA constant current source digital portometer. The blackbody furnace 1 is set at 500K, and the infrared rays from the furnace are converted to 13Hz by the rotary chopper 2.
is converted into alternating current and enters the detector 4. The signal from the detector is amplified by a low noise preamplifier 9 with a gain of 100 and input to a spectrum analyzer 10. As is well known, the responsiveness (v/w) of a detected word is determined by dividing the voltage (V) analyzed by the spectrum analyzer by the incident power (W) from the blackbody furnace.

As mentioned above, the temperature of the detector holder 5 can be lowered by reducing the pressure of the liquid nitrogen reservoir 7 using the pressure reducing device 8. FIG. 2 shows the relationship between responsiveness and temperature measured at a bias current of 8 mA. As can be seen from the figure, the responsivity continues to increase until the detector holder cools down to 62.5K, and below that, it decreases. Here, Joule heat H due to bias current
The temperature rise ΔT of the detector due to (Watt) is approximately expressed from the viewpoint of heat conduction as ΔT: IH/kA. Here, 1 is the thickness of the adhesive, k is the thermal conductivity of the adhesive, and A is the area of the detector. In this example, 1=4.5pm.

A=5X10-'am2, the thermal conductivity of the epoxy adhesive at liquid nitrogen temperature is ~1.4 mW/am-, so ΔT
~0°643H (H is in mW). When the bias current is 8 mA, H~20 mW, so ΔT~13. The temperature rise Δ of the detector itself obtained in this way
When T is added to the temperature of the detector holder that maximizes responsiveness, Tm = 62.5K, the temperature of the detector itself is T.
It becomes D near 5.5K. Table 1 shows the values of Δ'r, 'rm, 'r, ., obtained as a result of such measurements and considerations for several bias currents (IB).

As you can see from the table, as the I''-bias current increases, T
While m is decreasing, the temperature TD of the detector itself after correcting the influence of heat generation remains almost constant. Therefore, the data (Figure 3) in which the value of responsivity at Tm (K), that is, the maximum value, is plotted against the bias current represents the correct relationship between responsivity and bias current, corrected for the effects of heat generation. .

In the figure, the broken line indicates the theoretical responsivity curve of the integral photoconductive HgCdTe infrared detector.

This curve is the result of solving a one-dimensional diffusion equation under the boundary condition of ohmic contact.

The parameters used in the calculation are as follows. Measurement wavelength 1
0.9pm 7 oton background 8 x 1013ph
c1013ph, quantum efficiency 0.7, majority carrier concentration 1
015cm-3, minority carrier life 2.511sec,
Minority number table 1. The temperature rise ΔT of the detector itself for each bias current IB, the temperature Tm of the detector holder that maximizes the responsiveness, and the temperature TI of the detector itself expressed by the sum of these values. seeo Here, the majority carrier concentration was obtained by Hall measurement. In addition, the lifetime is determined by the line radiation of a semiconductor laser oscillated at high frequency.
It was obtained by irradiating the detector and displaying the output of the detector on a storage oscilloscope. The quantum efficiency is 0.7 considering the refractive index of the HgCdTe crystal since the detector used this time does not have an anti-reflection coating.
It is calculated as follows. The photon background is calculated from the situation where 300° of thermal radiation from the environment falls on the detector through the narrow band filter and diaphragm described above.

By using the above-mentioned evaluation method that corrects for the effects of heat generation, it becomes easy to compare measured data with theoretical values, and determine which parameters should be modified to effectively improve the performance of the detector. be able to.

Note that the present invention is not limited to the crystal materials, semiconductor types, wavelength bands, and cooling methods shown in the above embodiments, but is universally applicable to photoconductive detectors that require a large bias current. For example, the present invention can also be applied to a temperature control method using a detector circulation cooler made of single crystal Pb5nTe.

(Effects of the Invention) As explained above, according to the present invention, in evaluating the responsiveness of a photoconductive detector that generates a large amount of heat due to bias current, the temperature of the detector itself increases due to heat generation by lowering the temperature of the detector holder. This provides a correct relationship between responsiveness and bias current, which facilitates comparison of measured data with theory and allows efficient improvement of detector performance.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an infrared detector evaluation device for explaining the present invention in detail. 1 is a blackbody furnace, 2 is a chopper, 3 is a dewar-14 is a detector, 5 is a detector holder, 6
1 is a dewar, 7 is a liquid nitrogen reservoir, 8 is a pressure reducer, 9 is a preamplifier, 10 is a spectrum analyzer, 11 is a measuring fL
12 is a diaphragm, and 13 is a narrowband interference filter. FIG. 2 is a diagram showing the change in responsivity with respect to a bias current of 8 mA as the temperature of the detector holder is lowered. FIG. 3 is a diagram showing the relationship between responsivity and bias current after correcting the influence of heat generation. In the figure, black circles indicate measured data, and broken lines indicate theoretical values. FIG. 4 is a diagram showing a conventional evaluation method for an infrared detector, and the numbers in the diagram are the same as those in the explanation in FIG. 1. FIG. 5 is a diagram showing the relationship between responsivity and bias current when the temperature of the detector holder is maintained at 77K. 72 Figure Xlo6V/W Detector holder temperature IKI 73 Figure xlo6V/W Bias current (mAl

Claims (1)

[Claims] In a method for evaluating the sensitivity of a photoconductive infrared detector that generates a large amount of heat due to bias current, the method includes means for adjusting the temperature of the detector holder, and the output of the detector at several bias current values is determined as a function of the temperature of the detector holder. An evaluation method for an infrared detector, characterized in that the maximum output value is read from data obtained as a function of bias current, and the effects of heat generation are corrected by plotting them as a function of bias current.