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Introduction to Charged-Particle Detectors

Effects of Operating Temperature on Noise and Energy Resolution

ULTRA ion-implanted detectors, used primarily for alpha spectroscopy, are generally operated at room temperature. When optimum resolution is required, it is useful to reduce the detector noise by operation at low temperature. This is best accomplished by using surface barrier detectors instead of ULTRA detectors. The noise and energy resolution of surface barrier detectors can be substantially decreased by operating below room temperature, down to approximately –60°C. Below that temperature no further improvement is obtained because, with the leakage now »pA, the noise is dominated by the preamplifier noise and the detector capacitance, the latter, of course, not being a function of temperature. Figs. 1 and 2 show typical electronic noise and energy resolution measurements obtained with surface barrier detectors.

With ion-implanted ULTRA detectors, the noise is substantially lower at all temperatures, making them a clear choice at higher temperatures. The energy resolution increase that can be expected with ULTRAs at elevated temperature is approximately 15–20 keV FWHM at 60°C.

In some rare cases it is of interest to operate silicon detectors at temperatures below that of LN2, even down to <4 K. For such applications surface barrier detectors mounted with special cryogenic epoxy should be used. Totally depleted surface barrier detectors can be operated at such temperatures without adverse effects.1,2

1 M. Martini, T.A. McMath, I.L. Fowler, "The Effects of Operating Temperature on the Behavior of Semiconductor Detectors," IEEE Trans. on Nucl. Sci., Vol. NS-17, No. 3, pp. 139–148 (1970).
2 C. Canali, M. Martini, G. Ottaviani, A. Alberigi-Quaranta, "Measurement of the Average Energy per Electron-Hole Pair Generation in Silicon between 5 and 320 K," IEEE Trans. on Nucl. Sci., Vol. NS-19, N4, pp. 9–19 (1972).

fig8.jpg (29585 bytes)Fig. 1. Detector Noise and Alpha Energy Resolution as a Function of Temperature.

 

 

 

 

 

 

 

fig9.jpg (31652 bytes)Fig. 2. Detector Noise and Electron Energy Resolution as a Function of Temperature.