JPS6070774A - Detector for radiation - Google Patents

Abstract

PURPOSE:To improve radiation sensitivity and frequency response characteristics by bringing the thickness of a high resistivity P type CdTe crystal substrate to predetermined thickness so that a depletion layer generated in a CdTe crystal under a Schottky-barrier junction electrode reaches to an ohmic junction electrode. CONSTITUTION:When radiation is projected into a CdTe crystal substrate 1 from the Schottky-barrier junction electrode 2 side, free carriers generated in a depletion layer 4 are accelerated by an electric field in the depletion layer 4, and reach to a Schottky-barrier junction electrode 2, and ionization currents I are obtained through a lead wire 5. The resistance of P type CdTe crystal substrate 1 itself is not made to be contained substantially in the series resistance component of a detector because the depletion layer 4 reaches to an ohmic junction electrode 3 at that time. Consequently, the depletion layer 4 generated by a Schottky-barrier junction expands with the increase of the resistivity of the crystal substrate 1, and sensitivity is improved. Large substrate resistance hardly has an effect on the series resistance component of the detector by making the thickness (t) of the CdTe crystal substrate 1 the same as that of the depletion layer 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a radiation detector using a high resistivity P-type CdTe crystal substrate.

[Description of prior art]

FIG. 1 is a perspective view of the configuration of an example of a conventional X-ray detector of this type, and FIG. 2 is a sectional view of the main part.

This detector is constructed by forming a thin film electrode 2 having Schottky barrier characteristics on a high resistivity P-type CdTe crystal substrate 1, and forming an ohmic junction electrode 3 opposite to this. Electrode 2 and C
X-rays entering from the electrode 2 side are detected using a sensitive layer (depletion layer) 4 created by bonding with the dTe crystal substrate 1.

In a conventional detector with such a configuration, capacitance components such as junction capacitance, etc., which the detector has, and

There is a resistance in the part of the crystal substrate A that is not depleted in the CdTa crystal caused by the barrier, and a parasitic series resistance of the contact resistance, and these determine the frequency response characteristics of the detector, and the frequency response characteristic of the detector is determined by these. Response characteristics could not be obtained. Furthermore, in order to expand the sensitive layer of the detector and increase its X-ray sensitivity, it is necessary to use a high resistivity single crystal, and the substrate resistance increases the series resistance of the detector.

[Object of the present invention]

The present invention aims to realize a radiation detector that uses a high resistivity P-type CdTe crystal, has high radiation sensitivity, and has good frequency response characteristics.

[Summary of the invention]

The radiation detector according to the present invention has a structure in that the thickness of the CdTe crystal substrate is set to a predetermined thickness so that the depletion layer generated in the CdTe crystal under the Schottky barrier junction electrode reaches the ohmic junction electrode. It has characteristics.

[Explanation based on examples]

FIG. 6 is a side sectional view of essential parts showing an example of a radiation detector according to the present invention. In this figure, 1 is, for example, 3X1
A P-type CdTs crystal substrate with a high specific resistance of about 0.05 Ωam, 2 is formed on this CdTe crystal substrate by a method such as vacuum evaporation, and fc) Lt Schottky barrier junction electrode;
5 is formed on the other side of the CdTe crystal substrate, for example, A,
4 is a sensitive layer (depletion layer) formed under the Schottky barrier electrode 1, and 5 is a lead wire connected to each electrode.

In the detector of the present invention, the thickness t of the CdTe crystal substrate 1 is selected to be as thin as, for example, 0.25 nm, so that the sensitive layer 4 formed under the Schottky barrier electrode 1 forms an ohmic contact. It has reached electrode 3.

A detector configured in this manner is manufactured as follows.

First, CD and Te are mixed in chemical equivalents, vacuum sealed in a quartz glass ampoule, heated in a vertical Bridgman furnace, and the resulting single crystal ingot is cut into wafers. This was polished to a thickness of about 0.3 mm, chemically etched with a bromine methanol solution, and made to a thickness of 0.25 mm.
A CdTe crystal substrate of m is made. Next, the surface of the CdTe crystal substrate was sputter-etched with Ar ions and cleaned, and then a 20nrn thick film was vacuum-deposited with Schottky.
A barrier junction electrode 2 is formed.

Subsequently, gold chloride is applied to the other surface of the CdTe crystal substrate to form an Au ohmic electrode 3. Next, a lead wire 5f for signal extraction is connected to each electrode 2, 5 using, for example, a conductive adhesive to complete the process.

In the detector shown in FIG. 3, when radiation enters the CdTe crystal substrate 1 from the At Schottky barrier junction electrode 2 side, free carriers generated in the depletion layer 4 are accelerated by the electric field in the depletion layer 4. , a reaches the barrier junction electrode 2, and an ionizing current / is obtained via the lead wire 5. In the present invention, since the depletion layer 4 reaches the Au ohmic junction electrode 3, the series resistance component of the detector does not essentially include the resistance of the KP type CdTe crystal substrate 1 itself. Therefore, the thicker the specific resistance of the crystal substrate 1, the Schottky
The depletion layer 4 generated by the barrier junction becomes larger, increasing the sensitivity. At the same time, by setting the thickness t of the CdTe crystal substrate 1 to the width of the depletion layer 4, the large substrate resistance hardly affects the series resistance component of the detector. It disappears. Therefore, the frequency response characteristic of the detector, which is determined by the series resistance component of the detector and the capacitance such as the junction capacitance, can be improved.

In Figure 4, the thickness t of the crystal substrate is 155 mm, 0.53
mrn.

The frequency response characteristics obtained by changing the width to 0.25 mm are shown. According to the experimental results, the one with a thickness of tf O of 25 nm, that is, the one configured so that the depletion layer reached the ohmic junction electrode, had the best frequency response characteristics.

[Effects of the present invention]

As explained above, according to the present invention, a radiation detector having high radiation sensitivity and good frequency response characteristics can be realized.

[Brief explanation of drawings]

FIG. 1 is a perspective view of the configuration of an example of a conventional detector, FIG. 2 is a cross-sectional view of the main parts thereof, FIG. 5 is a side cross-sectional view of the main parts of an example of the detector according to the present invention, and FIG. is a characteristic diagram showing an example of experimental results. 1... P-type CdTe crystal substrate, 2... Schottky
Barrier junction electrode, 3... Ohmic junction electrode, 4...
・Depletion layer, 5... Lead wire.

Claims (1)

[Claims] (1) In a radiation detector in which a Schottky barrier junction electrode is formed on one surface of a high resistivity P-type CdTe crystal substrate and an Ohmink junction electrode is formed on the other surface, the thickness of the P-type CdTe crystal substrate , the Schottky
The depletion layer generated in the CdTa crystal under the barrier junction electrode is
A radiation detector characterized in that a predetermined thickness is selected so as to reach the ohmic junction electrode.