DD300682A7

DD300682A7 - Si (Li) -Driftdetektor

Info

Publication number: DD300682A7
Application number: DD25187383A
Authority: DD
Inventors: Klaus Matauschek; Klaus Schwerd; Barbara Adolphi; Waltraut Friedrich
Original assignee: Robotron Messelekt
Priority date: 1983-06-09
Filing date: 1983-06-09
Publication date: 1992-07-02

Abstract

Die Erfindung beinhaltet einen Si(Li)-Driftdetektor und betrifft das Gebiet der Kernstrahlungsdetektoren auf Halbleiterbasis. Ziel der Erfindung ist ein Detektor mit verbesserter Langzeit- und Temperaturstabilität sowie verringertem Materialeinsatz. Die Erfindung löst die Aufgabe, Instabilitäten von Sperrstrom und Rauschen, die durch die Eigenschaften der sperrenden p-leitenden Schicht und ihrer Kontaktierung bedingt sind, durch konstruktive Maßnahmen zu beseitigen. Das Wesen der Erfindung besteht darin, daß der Si(Li)-Driftdetektor eine p-leitende Schicht mit einem Widerstand von maximal 100 Ohm besitzt, auf die erfindungsgemäß die metallische Kontaktschicht auf diejenigen Flächen der p-leitenden Schicht begrenzt ist, die mit dem p-leitenden Gebiet des Siliziumkörpers verbunden sind, der bei angelegter Sperrspannung feldfrei bleibt. Durch Ausbildung des Detektors in Form eines Streifens wird die erforderliche Siliziummenge pro Detektor verringert. Die Erfindung kann für die Aufklärung, Warnung und Kontrolle von Kernstrahlungsfeldern angewendet werden.The invention includes a Si (Li) drift detector and relates to the field of semiconductor-based nuclear radiation detectors. The aim of the invention is a detector with improved long-term and temperature stability and reduced use of materials. The invention solves the problem of eliminating instabilities of reverse current and noise, which are due to the properties of the blocking p-type layer and its contacting, by constructive measures. The essence of the invention is that the Si (Li) drift detector has a p-type layer with a maximum resistance of 100 ohms, according to the invention, the metallic contact layer is limited to those areas of the p-type layer, which with the p Conductive region of the silicon body are connected, which remains field-free with applied reverse voltage. By forming the detector in the form of a strip, the required amount of silicon per detector is reduced. The invention may be used for the detection, warning and control of nuclear radiation fields.

Description

Kontaktschicht auf dem p-leitenden Teil des Siliziumkörpers angeordnet ist. Wird an einen Detektor dieser Art die für den Betrieb erforderliche Speerspannung angelegt, so bildet sich das elektrische Feld nur in dem Bereich der p-leitenden Schicht aus, der keine metallische Kontaktschicht besitzt. Während des Driftprozesses reicht die Querleittähigkeit der p-Schicht aus, um eine ausreichend homogene Kompensation zu erzeugen. Während des Betriebes können die oben beschriebenen „Kurzschlüsse" an den Fehlstellen nicht mehr auftreten. Damit wird eine hohe Temperatur- und Langzeitstabilität erreicht. Ferne' ist es möglich, den Si(Li)-D.^Tiftdetektcr in Form eines Streifens auszubilden, bei dem die metallische Kontaktschicht im Bereich eines Endteils des Streifens angeordnet ist. Gegenüber den üblichen rotationssymmetrischen Strukturen verringert sich damit dsr Anteil dos für den Strahlungsnachweis „toten" Volumens. Für einen Detektor dieser Konstruktion wird bei der Herstellung eine verringerte Siliziummenge benötigt.Contact layer is disposed on the p-type part of the silicon body. If the spear voltage required for operation is applied to a detector of this kind, the electric field is formed only in the region of the p-type layer which has no metallic contact layer. During the drift process, the transverse conductivity of the p-layer is sufficient to produce a sufficiently homogeneous compensation. The "short circuits" at the defects described above can during operation no longer occur. Thus a high temperature and long term stability is achieved. Distance 'it is possible to use the Si (Li) D. Form ^T iftdetektcr in the form of a strip, wherein In contrast to the conventional rotationally symmetrical structures, the proportion of dos for the radiation detection of "dead" volume is reduced. For a detector of this construction, a reduced amount of silicon is needed during manufacture.

exemplary

Die Erfindung soll nachstehend an einem Ausführungsbeispiel sowie anhand einer Zeichnung näher erläutert werdGn. Ein streifenförmiger Siliziumkörper mit einer Abmessung von 25mm Länge, 1 mm Dicke und omrr. Breite besitzt eine lithiumdiffundierte Schicht 1 mit einer Dicke von 200 pm und einer Länge von 20 mm. Sie ist η-leitend und mit einer metallischen Kontaktschicht 2 (z.B. aus Nickel) versehen.The invention will be explained below with reference to an exemplary embodiment and with reference to a drawing. A strip-shaped silicon body with a dimension of 25mm length, 1 mm thickness and omrr. Width has a lithium-diffused layer 1 with a thickness of 200 pm and a length of 20 mm. It is η-conductive and provided with a metallic contact layer 2 (e.g., nickel).

Unter der lithiumdiffundierten Schicht 1 befindet sich das durch lonendrift kompensierte Gebiet 3, dessen spezifischer Widerstand im Bereich von lOOkOhmcm liegt. Die gesamte, dei lithiumdiffundierten Schicht 1 gegenüberliegende Fläche des Siliziumkörpers besitzt eine sperrende p-leitende Schicht 4 aus Platinsilizid mit einem Schichtwiderstand von 250hm. Die metallische Kontaktschicht 5 (z. B. aus Nickel) ist mit der p-leitenden Schicht 4 auf den Dockflächen des p-leitenden Gebietes 6 verbunden, das aus dem Ausgangsmaterial, p-dotiertem Silizium mit einem spezifischen Widerstand von 1 kOhmcm, besteht. Nach dem Anlegen der Sperrspannung bildet sich das elektrische Feld nur im Bereich des kompensierten Gebietes 3 aus. Dio Verbindungsstellen der p-leitenden Schicht 4 und der metallischen Kontaktschicht 5 sowie der metallischen Kontaktschicht 5 und dem p-leitenden Gebiet β sind feldfrei. Detektoren dieser Konstruktion zeigen bei Temperaturen um 55°C nach 1000 Betriebsstunden Rauschhalbwertsbreiten von 25keV. Dies ermöglicht dio Zählung von Gammaquanten von minimal 80keV.Below the lithium-diffused layer 1 is the area 3 compensated by ion drift, the resistivity of which is in the range of 100 kOhmcm. The entire, the lithium-diffused layer 1 opposite surface of the silicon body has a blocking p-type layer 4 of platinum silicide with a sheet resistance of 250hm. The metallic contact layer 5 (eg made of nickel) is connected to the p-type layer 4 on the docking surfaces of the p-type region 6, which consists of the starting material, p-doped silicon with a resistivity of 1 kOhmcm. After applying the blocking voltage, the electric field is formed only in the region of the compensated region 3. Dio connection points of the p-type layer 4 and the metallic contact layer 5 and the metallic contact layer 5 and the p-type region β are field-free. Detectors of this construction show noise half-value widths of 25keV at temperatures around 55 ° C after 1000 operating hours. This allows the counting of gamma quanta of a minimum of 80keV.

Claims

1. Si (Li) -Driftdetektor, provided with a p-type layer having a sheet resistance of 100 ohms maximum, characterized in that the metallic contact layer (5) on the p-type region (6) is arranged so that they themselves on the p-type layer (4) and / or on the surface of the p-type region (6).

2. Si (Li) -Driftdetektor according to item 1, characterized in that the silicon body has the shape of a strip, of the sin end portion is formed as a p-type region (6) on which the metallic contact layer (5) is arranged.

3. Si (Li) -Driftdetektor according to item 1 and 2, characterized in that at least two boundary surfaces of the silicon body are both Begrenzungsfiächen the compensated area (3).

For this 1 page drawing

Field of application of the invention

The invention relates to nuclear radiation detectors for the detection, warning and control of gamma radiation fields and the dosimetric monitoring of nuclear power and radionuclide plants,

Characteristic of the known state of the art

Lithium-drilled silicon nucleation detectors, also known as Si (Li) drift detectors, are predominantly made with a deposited gold layer that acts as a pervious surface barrier. Detectors of this type are described by H. Süker, "Theory and Practice of Semiconductor Detectors", Springer-Verlag 1971, pp. 121 to 139 and pages 182 to 187. The disadvantages of such detectors are their high reverse currents at elevated temperatures continue to increase in operation for a long time. This is already required at temperatures above 40 ⁰ C for suppressing noise pulses Diskriminatorenergien of more than lOOkeV so that gamma rays with energies below 100 keV are no longer detectable. Similar constructions where blocking p-type layers are produced by diffusion, ion implantation or alloying and are over-evaporated for contacting and increasing the transverse conductivity with a metal layer, show a similar temperature and long-term behavior as those Denors that have a gold surface barrier.

Object of the invention

The aim of the invention is to improve the temperature and long-term stability and to keep the amount of silicon used per detector as small as possible.

Explanation of the essence of the invention

The invention solves the problem of providing Si (Li) -Driftdetektoren with a temporally and even at elevated temperature stably blocking p-lcitenden layer. Si (Li) drift detectors are pin diodes in which the η-region is made by diffusion of lithium with a thickness of about 0.1 to 0.3 mm. This layer does not change its barrier properties during operation. The i-region is formed during production in the ion drift process by compensation of Borstörstellen by lithium and is therefore referred to as a compensated region. When the required blocking p-type layer is formed by vapor deposition of gold, a blocking surface barrier is formed at the silicon-gold interface by bonding oxygen. The binding de? Oxygen, however, increases with increasing temperature .ib. At the same time, the existing low mobility of the lithium ions in the silicon lattice is sufficient to partially compensate for the p-conduction. The incipient injection of charge carriers increases the reverse current and in particular the noise. If the p-layer as stated above z. B. produced by ion implantation of boron and vapor-deposited with a metal contact, so these detectors have at room temperature small reverse currents and a low noise pulse level. The metal contact is required for a low-noise contacting of the p-type layer. It was also applied for a reduction in the transverse conductivity of the p-layer during the ion drift process, which occurs at 120 ° C. Too high film resistances result in an inhomogeneous compensation of the boron noise. Detectors with the latter on construction of the p-type layer also operate at temperatures in the range of 5O ⁰ C unstable. The reason for this are defects in the p-type layer. These are unavoidable with large-area components. These include nuclear radiation detectors, whose sensitive surfaces are usually more than 100mm *. At the defects caused by the obon mentioned migration of lithium ions "shorts" between compensated silicon and the metal contact layer during operation.

The features of the invention are that the Si (Li) -Driftdetektor has a p-type barrier layer with a low sheet resistance, which is provided according to the invention with a metallic contact layer, dl ·? is limited to those surfaces of the ρ conductive layer, which are connected to the p-type part of the silicon body orfer that the metallic