JPS5812374A - Semiconductor detector - Google Patents

Abstract

PURPOSE:To obtain a semiconductor detector of large output, high sensitivity, and high efficiency by a method wherein a metal layer is formed on a P type layer thin and moreover in structure as to enable to prevent reduction of sensitivity as much as possible. CONSTITUTION:At a diode having P-N<->-N<+> structure, a metal 11 is formed uniformly on the P type layer 3, and in condition having ohmic contact with the P type layer 3, and a current flows from the P type layer 3, the metal layer 11, and a metal electrode 5 to a load resistor 6. As the material for the metal layer 11, a material being easy to make electrons to pass through like aluminum, and moreover having high electric conductivity is desirable. By providing the metal layer 11 like this, reduction of series resistance of the device can be attained without reducing sensitivity of the diode remarkably, large output current, namely large output can be obtained, and efficiency can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor detector for detecting electron beams, X-rays, etc. Recently, semiconductor detectors (SSD) have been used to detect electrons. Compared to previously used scintillators, this detector is small, has a simple structure, and is easy to handle. It can also be used for detection.

Such detectors often have the structure shown in Figure 1 ◇ In Figure 1, l is an n-layer substrate, 2 is an n-layer substrate, and a
tf p layer, 4 is silicon dioxide layer, 5 is metal electrode, 6
is a load resistance, and 7 is a bias power supply.

Here, explanation will be given by taking electrons as an example of the object to be detected. Electrons enter a region surrounded by the ring-shaped metal electrode 5. The electron penetrates into the 9 layer 3 and the n layer 2 according to its energy, and one electron creates one electron-hole pair per energy of 3.6 eV, corresponding to the energy.
This flows to the external circuit and generates a voltage drop across the load resistor 6. Furthermore, even higher sensitivity can be obtained by increasing the power supply voltage and causing avalanche breakdown to occur when electrons are incident.

In the case of a diode having such a structure, in order to operate at a high frequency and at the same time obtain a large current gain, that is, high sensitivity, the thickness of the p-soil layer 3 is made as thin as possible, for example, 0.1 to 0.2 pm. However, the resistance of the p-soil layer 3 is relatively high at 100 ΩcIR (impurity concentration 10"), so the output current is large. When K is 0, the voltage drop becomes large in this part, resulting in a decrease in the output voltage and output power, and the heat generation in this part causes the temperature of the passive vice to rise. This has the drawbacks of increased loss and limited frequency characteristics.

The present invention solves these drawbacks by forming a thin metal layer on the p-layer and having a structure that prevents a decrease in sensitivity as much as possible, thereby achieving high output.

The aim is to realize a highly sensitive and highly efficient semiconductor detector.

The present invention will be described in detail below with reference to the drawings. FIG. 2 shows an embodiment of the present invention, and 11 is a metal layer. This metal layer 11
is uniformly formed on the two layers 3 and is in ohmic contact with the two layers 3. Current flows through two layers 3, metal layer 11, metal electrode 5
and flows to the load resistor 6. - It is desirable for the material of the metal layer 11 to be a material that allows electrons to pass through easily and has high electrical conductivity, such as aluminum. Now, set the thickness of layer 2 to 0.
1 μm # impurity concentration 1020. /-, then 2 layers 3
The sheet resistance of 500 H thick aluminum is 5.3 x 10-107 holes, so the series resistance of the diode is significantly reduced. When a diode with the structure shown in FIG. When the same electron beam is irradiated onto a diode having the structure, the reflected electron beam energy is about 1.11 KeV, and the energy loss is only 0.2 KeV (2Δ qib> of the beam energy).

3(A) and 3(B) are a cross-sectional view and a plan view showing another embodiment of the present invention.0 The metal electrode 5 is formed thickly in the shape of a ring around the area where the electrons are irradiated. . metal layer 11
is made thinner in the center than in the periphery. Assuming that the electron beam is uniformly irradiated inside the metal electrode 5, the diode current generated in the center portion flows from the second layer 3 through the metal layer 11 to the nearest metal electrode 5.

The diode current generated in the peripheral area also reaches the metal layer 11 above it from the second layer 3 and flows into the nearest metal electrode.When an electron beam with a uniform current density is irradiated in this way, the metal layer 11 flows in the peripheral area. The current density increases. In reality, the metal layer 11 increases in proportion to the radius. Therefore, even if the thickness of the metal layer 11 at the center is made thinner than that at the periphery, the effect of increase in sheet resistance is smaller than when it is uniform. Since the loss of the incident beam in the metal layer 11 can be reduced, the sensitivity can be increased. Also, the same effect can be obtained even if the thickness of the inner thin part of the metal layer 11 is 0, that is, the metal layer 11 in this part is omitted. An example of a metal layer structure based on the same idea is shown below. In FIG. 4, the hatched areas are thick parts of the metal layer, and the unshaded areas are areas where the metal layer is thin or absent. In Figure 4, a region of low resistance is created in the shaded area, and a region of relatively high sensitivity is created in the non-shaded area, thereby realizing a semiconductor detector with overall high sensitivity and low series resistance. In addition to the structures shown in Figures 3 and 4, it is possible to create structures other than those shown in Figures 3 and 4 by adding a metal layer partially or distributing metal layers of different thickness in the area that is irradiated with electrons. It is clear that the concept of the present invention includes a configuration of the metal layer that has the effect of reducing the series resistance without significantly reducing the sensitivity.

In the embodiment shown here, a diode with a p-n--n+ structure was explained, but it is clear that the idea of the present invention can be applied in exactly the same way to a diode with an n-1)--p layer structure. Furthermore, in the embodiment, the operation was explained as an electron detector, but the idea of the present invention can be applied to a detector for X-rays, light, and radiation in addition to electrons.

Furthermore, it is clear that the idea of the present invention can also be applied to a semiconductor device that combines a semiconductor and an electron beam or a light beam.

As explained above, in the present invention, it is possible to reduce the series resistance of the device without significantly reducing the sensitivity, so a large output current, that is, a large output, can be achieved, and efficiency can be improved. Since the loss of high frequency signals is reduced, there are advantages such as higher frequencies can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional semiconductor detector, FIG. 2 is a sectional view of an embodiment of the semiconductor detector of the present invention, and FIGS.
) are a sectional view and a plan view of another embodiment of the present invention, and FIG. 4 (
A) and (B) are structural diagrams showing specific examples of metal layers used in the semiconductor detector of the present invention. 01...n soil layer substrate, 2.
...N single layer, 3...P layer, 4...silicon dioxide layer, 5...metal electrode, 6...load resistance,
7...Bias power supply, 11...Metal layer. Patent applicant Nippon Telegraph and Telephone Public Corporation agent Tsuneo Shiramizu and one other person Figure 1 Figure 2 Fang 3 times

Claims (2)

[Claims] (1) In a semiconductor device comprising a semiconductor having a first conductive characteristic and a semiconductor layer having a second conductive characteristic partially existing on the surface of the semiconductor having the first conductive characteristic, A semiconductor detector characterized in that a metal layer having a thickness through which an object to be detected can easily pass is formed on the surface of a semiconductor layer having second conductive properties. (2) The semiconductor detector 0 according to claim 1, characterized in that the thickness of the metal layer is partially changed or the metal layer is partially removed.