V A R I O U S C H A R A C T E R I S T I C S

OF S I L I C O N D I F F U S I O N - D R I F T E D D E T E C T O R S

~. K. S t e p a n o v , Bo Po S m i r n o v , a n d N V q ' y u t i k o v

UDC 621.38%462

In the spectrometry of B-radiation wide use is made of silicon diffusion-drifted detectors with a surface bar- rier. !t is therefore of interest to stud}, the influence of different conditions of the experiment on various character- istics of these detectors and to determine the relationships between these characteristics.

For the measurements we took several silicon diffusion-drifted detectors made of p-type silicon with a rests- ttvity of .500 fa " cm and a thickness of the sensitive region equal to 2 mm. Such detectors can be used in spectrom-

etry of ~-radiat ion wieh an energy up to 1 MeV, and also tn spectrometry of soft x-rays and 7-radiatt~ The sen- sitive area of the chosen detectors was as follows: 20 mm 2 for the detectors Nos. 252 and 276; 125 mm ~ for Nos. 197 and 256, and 250 mm z for detector No. 238.

The detectors were developed by a team under the direction of A. V. yurovskii.

It is well known that semiconductor detectors exhibit optimal spectrometric properties when cooled, since the cooling of the detector leads to a decrease in the reverse currents [1]. This circumstance was taken into account in

the measurement of the range of the working voltages. This measurement was made in the vacuum chamber of a

g-spectrometer with a semiconductor detector. The mounting stand, set up in the chamber, ensured cooling of the

detector which was fixed to it to a temperature of 150-160~ The noise of the electronic part of the spectrom- eter used in the experiment was 2.7 keV in the energy equivalent for zero input capacitance.

Monoenergetic electrons were obtained from spectrometric taTCs internal conversion electron sources. Analy-

sis of the curves of the dependences of the energy resoludon on the bias voltage, obtained for detectors cooled to

i60~ showed tlmt for them (with the exception of No. 238) the lower l imit of the working voltage was equal to

100 V, and the upper l imit of the range in which the energy resolution did not change significantly was of the order

of 300 V,

For detector No. 238 which had a large sensitive area, the dependence of the resolution on the voltage had

a more characteristic form: the range of working voltages was not large (~ 50 V) and was displaced toward lower

voltages. The result of the measurements indicates that the influence of the reverse current on the resolution in

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Fig. 1

this case is manifested much more strongly as the voltage increases than in

the case of detectors with a smailer area.

Analysts of the characteristics of the domestic diffusion-drifted de- tectors showed that the ques[ion of the influence of the detector tempera-

ture on the energy resolution requires further elucidation. In this connec-

t ion we obtained the characteristics of the energy resolution of the detec-

tors as a ftmction of their temperature. The temperature measurements

were carried out in the vacuum chamber of a ~-spectrometer. The change

in the temperature was due to the natural heating of the previously cooled

detector. The detector temperature was controlled by a copper-constantan

thermocouple fixed to the frame of the detector. The spectrometric laCs internal conversion electron sources were selected in advance on the basis

of their activity in such a way that the spectrum could be obtained during a short t ime (1-2 min). During the course of this t ime, the change in the temperature of the detector was not large (from 2 to 6"). The energy reso- lution of the spectrum was then referred to the average temperature. Dur- ing the complete cycle of measurements, the stability of the electronic

Translamd from Izmeri te i 'naya Tektmika, No. 3, po 106, March, 1989. Originalar t icle submitted February22,

1968.

457

circuit was controlled by means of a generator of stable amplitude. The energy resolution was measured at

a fixed voltage U = 125 V.

The results of the measurements of the energy resolution of the different detectors as functions of the temper-

ature are shown in Fig. 1. In the same way we obtained the dependences of the reverse currents of the detectors on

their temperature. Analyzing the results of the measurements, we arrived at the following conclusions:

1. There exists for the detectors a definite temperature range (220-230~ below which the energy resolution

does not change significantly.

2. A sharp increase in the reverse current occurs at temperatures above 220-230*K. Consequently, the worsen-

ing of the energy resolution as the temperature is increased is connected, as one would expect , with an increase in

the reverse current.

The reverse current exerts a decisive influence on the energy resolution. It is therefore expedient to deter-

mine the influence on the current-vol tage characteristic of various conditions of the experiment: a) room tempera-

ture and atmospheric pressure; b) room temperature and vacuum; c) cooling to 160~ and vacuum.

The results of the measurements showed that the current-vol tage characteristics for the cases a and b) are the

same, and that cooling decreases the reverse current by more than two orders of magnitude.

The results obtained on the optimal working temperature, the range of the working voltages and the current-

voltage characteristics under different conditions show that these data are typical for this type of detector.

1.

LITERATURE C I T E D

F. J. Waiter, J. W. T. Dabbs, and L. D. Roberts, Solid State Radiation Detectors, Inst. of Radio Engineers, New

york (1961).

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