Sensors and Actuators, 5 (1984) 103 - 117

103

REVIEW OF SEMICONDUCTOR DETECTORS FOR NUCLEARRADIATION

P A TOVEElectronic Department, Institute of Technology, University of Uppsala, Uppsala (Sweden)

(Received February 23, 1983, accepted in revised form September 6, 1983)

Abstract

The basic requirements on semiconductor materials for nuclear radia-tion detectors are reviewed Comparison between the different propertieswith respect to energy resolution, y-detection efficiency, low energy X-raydetection, room temperature performance etc for detectors of Si, Ge or lesscommon materials such as HgI 2 , CdTe, GaAs, diamond etc is based onmaterial parameters such as bandgap, atomic number of the constituents,carrier mobility and lifetime and degree of crystal purity and perfectionobtainable

The influence of noise sources in the detector and preamplifier onspectrometer resolution is treated with a simple model, which also clarifiesthe influence of material properties This gives a background for under-standing present development work in which the common Si and Ge detec-tors are replaced by other materials in specific detection situations

The advantages then gained are illustrated by a brief discussion of theobtained performance for some newer designs described in the literature,including semiconductor scintillation counters

1 . Introduction

Radiation detectors make special demands on the semiconductor ma-terial, these demands are somewhat different from those required for othersemiconductor devices The most common principle is to make a pn-junction or a metal semiconductor junction (surface barrier diode) on verylow-doped material [1 - 3] The junction is reverse biased so that a thickdepletion layer is formed where the field is high and at the same time theleakage current is low The free electron-hole pairs created by the ionizingparticle (or other radiation) are collected in the field and give a current pulsewhich is detected with a charge-sensitive amplifier, see Fig 1

0250-6874/84/$3 00

© Elsevier Sequoia/Pnnted m The Netherlands

104

biassignal

,--Af III I~\)r" -- n s,

Fig 1 Basic principle of a semiconductor detector

A few mile-stones in the development of detectors are listed m Table 1The relationship between the demands on the semiconductor material

and the performance of the detector is shown in Table 2Silicon and germanium semiconductors have been fabricated m the

most pure form and as near-perfect monocrystals They therefore fulfilldemands 1 and 4 and form the basis of most of the present detectors The

ionizing particle

1

Low net concentration of doping -' Sufficiently thick depletion layers to stopatoms

the radiation can be obtained

2 Large bandgap -• Leakage current becomes sufficiently low,making room-temperature operation pos-sible, for example

3 High atomic number - Short absorption length for y, also for rela-tively high -1-energy, ,y-radiation can be de-tected with high efficiency

4

Long drift-length ('Schubweg) µPT, -+ Effective charge collection, the signal be-preferably ' the depletion width

comes independent of where in the detectorw, for both electrons and holes ({t

the radiation is absorbed, hence good energy= mobility, F = field, 7 = earner

resolutionlifetime)

TABLE 1

Germanium surface barrier detector for a-particles 1955 (J W Mayer)Silicon surface barrier detector for a-particles 1958Lithium-drifted p-silicon detector 1960Lithium-drifted p-germanium detector 1962High purity germanium detector 1970CdTe detector 1966GaAs detector 1970Exotic materials HgI2 , PbO etc 1972Improved planar detector in silicon 1980

TABLE 2

Demands

Performance

most common products are surface barrier Si detectors for general purpose,room-temperature operation, and 'high-punty' or Li-drifted [2, 3] (compen-sated) Ge detectors for -y-detection at liquid N 2 temperature The desire forimprovements, mainly with respect to points 2 and 3, motivates a closerlook at the whole situation, this is done in Section 2

2. Influence of material parameters

2 1 Low net dopingThe maximum obtainable depletion width for a one-sided abrupt junc-

tion is given approximately by [4]

w = 2 X 10 12/IND-NA B cm

where IND -NA B is the net doping concentration, in cni3 , of the lightlydoped side This expression follows from the usual expression for depletionwidth, combined with the requirement that the maximum field strength,which is obtained at the junction itself, must be smaller than the avalanchefield strength

Approximate net dopmgs obtainable with different materials appearin Table 3

TABLE 3

Material

High purity silicon [6, 6]Lithium-compensated silicon or germanium [7] (77 K)High-purity germanium [8, 9] (77 K)

CdTe

High purity [ 10]tCompensated [10, 11]

GaAs [12 ] ( Epi-layer (< 200 gm)l Bulk (< lmm)

SiC [13]HgI2Diamond

105

Net doping, INn - NAI CM-3

3 X 10t 0>los>5X109

10 12 . 10 13< 1010

10 13

1012

1019 .1017SeaminsulatingInsulating

2 2 Bandgap and atomic numberIn reverse-biased junctions with thick depletion layers of the type in use

here, thermally generated current in this layer may become important Thiscurrent can be comparable with, or larger than, the usual diffusion currentin a pn-junction or the Schottky current in a surface barrier detector [14]

106

The generation current becomes small for large bandgap and long carrierlifetime This is one reason why silicon is better than germanium for room-temperature detectors, only by cooling to liquid nitrogen temperature canthe leakage current for Ge be brought down to negligible values Leakagecurrents for surface barrier detectors, at room temperature, per em 2 detectorarea, are listed in Table 4 For Si, manufacturers' data were used

TABLE 4

Silicon*, e g, surface barrier

GaAs

CdTe

Hgi2

C diamonddetector0 1 pA/0 1 mm depletion

-0 05 pA/

-10-7 - 10-8 A -10-1e A -0layer

0 1 mm [27] [11, 15]

fill

*In extreme cases 1 nA/0 1 mm has been obtained [16] for Si planar detectors, whichcorresponds to a earner lifetime of - 15 ms'

However, a large bandgap means that the energy e required for genera-tion of one electron-hole pair increases The number of generated electron-hole pairs, N=E/e (for radiation with energy E) then becomes smaller Inprinciple a increases linearly with the bandgap The atomic number Z is ofimportance for the absorption depth of the radiation The absorption depthfor photoelectric absorption, which is utilized in X-ray and gamma spectros-copy, vanes as Z -5 For particles, e g, a-particles, the ionization-loss dE/dxvaries approximately as Z Gamma-radiation and particles are absorbeddifferently While gamma quanta are removed one by one from the incom-ing radiation beam and give rise to a photo-electron (or a Compton electron,which is not so favourable), the energy of an a-particle decreases successivelyduring the passage through the material by energy loss to electrons removedfrom nearby semiconductor atoms The bandgap, energy-loss parameter eand atomic number vary for different materials according to Table 5

TABLE 5

Material Bandgap 6 = energy loss/ Atomic number Z(eV) electron-hole pair (eV) [7]

Ge 0 66 3 0 32Si 1 1 3 65 14CdTe 1 4 4 4 48,52GaAs 1 4 4 7 31,33sic 22-33 9 14,6HgI2 2 1 4 2 80, 53C --6 17 6

1 0 7

2 3 Drift length (Schubweg)The drift length must be larger than the length the carriers have to

migrate in the depletion layer in order to be collected Values for differentmaterials are given in Table 6

Consider a cloud of careers formed close to one electrode by shallowabsorbed radiation The original charge qN o decreases during the transporttowards the other electrode, at x = w, according to

N=No exp(-t/T)

According to Ramo's theorem, the change in induced charge on the elec-trodes at time t when the cloud moves through dx, is SQ where SQ/qN=dx/w . Thus

i(t) = dQ = qNOoo exp(-t/T)aand the collected charge

wfpF

qNo w

gNOpFTQ = f i(t)dt = - f exp(-x/µFT) dx = {1 -exp(-w/µFT)}

t=o

W x-o

W

With Q 0 = qNo we obtain

Q µFT

Q0=w

{1 - exp(-W/µFT)}

This is Hecht's relation [21]To verify that both Le and Lh have to be large - consider two ionizing

particles with the same energy Eo which hit the detector at different places,see Fig. 3 The particles give the same collected charge, and the detectorcan be used for spectroscopy only if µFT/w is large for both electronsand holes

TABLE 6

Material Drift length Le,h = Pe,hTe,hF (F = field strength)

$1, Ge - 1 m

GaAs, CdTe, Hg12 _ 1 mmCdTe per, < 3 X 10-3,

phTh < 4 x j 0 -°ZCm2 V

C

HgIZ per, < 2 X 10 , PhTh < 10' Cm /V,Pee eg, [17-19]

-1 mm, µ ere and MhTh - 10-6 - 5 x 10-6 cm2 /V [20]

GaP, InP, PbO, Pbi 2 etc --1 µm

1 08

electronsti

uFT/w

holes

f + + + + + T f' E0aFI I I II11 1a1

04

10

4

8

Fig 2 Hecht's relation

Fig 3 Particles incident at two positions parallel to the electrodes of a detector

An exception to this is for shallow absorbed radiation close to oneelectrode, where only one type of carriers has to be collected, good spectro-meter resolution is still obtained A practical case is absorption of low-energy X-rays in an HgI 2 detector

3 Spectrometer resolution

Ideally, all radiation events with the energy E should give rise to pulsesof exactly the same height, i e , the energy resolution should be infinitelygood But even if pFTlw is large, the spectrometer resolution may be lessthan perfect because of the following reasons

(1) Statistical spread = (N X the Fano factor)' i2 in N where N = thenumber of generated electron-hole pairs and the Fano factor is = 0 1 Thisspread depends on the energy E of the radiation and the energy-loss param-eter e = E/N

(2) Noise component i„ 2 = 2qIB of the leakage current I of the detec-tor B is the amplifier bandwidth, see Fig 4

(3) Noise m the amplifier, most often a charge-sensitive preamplifier,using a JFET in the input stage The noise can usually be described by anoise resistance r8 , see Fig 4

Noise under (2) is mostly parallel noise, whereas type (3) is oftenseries noise Figure 5 visualizes these two sources as randomly spaced pulses(from individual electrons) It is seen that parallel noise decreases for shortTd while series noise decreases for large T, where Td is the differentiation tuneconstant and T, is the integration time constant Figure 5 also shows how Td

and T, reduce the bandwidth by influencing the lower and upper limits,respectively An analysis shows that the optimum noise situation is generallyobtained with equal time constants, 1 e , Ti = rd = T.* Figure 6 illustrates

also influences the signal amplitude

1000eV

100eV

10eV

Fig 4 Noise sources, amplifier and pulse shaping networks

T

fl-l/tTd>n

d

`

Parallel n

n n n

n °~Srfnoise

it

sr-•

Parallel noise decreases for short Td

fromleakagecurrent)

series vn n

f1

n n

n

n

IL S fu f

noes

`e

T

from

tut

Series noise decreases for large i i

shot noisein the input FET)

Fig 5 Schematic picture of the influence of Td and r, on the amplitude of parallel- andseries-type noise

(AE)

=energy resolutionFWHM

C=10 pF (detector - FET) assumed

wide band amplifier

parallel noise fromleakage current

contribution from statisticalspread in the number ofelectron-hole pairs (theexample of E=500 eV into 5i,with Fano factor 0 1, is drawn)

1 09

III1IItt T'. T , ~ Td

Was

10-7

10-6

10-5

10-4

10-3

Fig 6 Schematic picture of different contributions to the line width in a spectrum, andthe influence of the amplifier time constants (assuming r, = Td)

1 10

how the two types of noise vary with Ta and influence the energy resolution[22] The optimum choice of Ta = Td = T, obviously depends on the magni-tude of the two noise components in a particular case, and it is found inthe valley between two lines with opposite slopes

All three contributions (1), (2) and (3) to the spectrometer line widthare illustrated m Fig 6 They add quadratically and vary as

(AE)statistical cc (FE) 1/2(AE)paranel cc (ITa ) 1/2

(AE)senes a (TrsC 2 /Ta)1/2 where Tis charge collection timeThe leakage current in the detector is quite important in determining

optimum time constants From Fig 6 we see that for a Si-detector at roomtemperature with I ~ 5 X 10 -1 A, Ta can be chosen short (this means that ahigh pulse rate can be allowed), while a cooled Ge-detector with I= 5 X10-14 A requires a longer Ta , but also gives better energy resolution

4 Examples of detector applications

We can illustrate the previous discussion with a few examples of newdevelopments and some spectra taken with different detectors

(1) Figure 7 shows a simple set up for X-ray fluorescence measure-ments, for identification of materials or ores [23] Figure 8 shows how theX-ray fluorescence spectra look if "Fe with the gamma-energy 5 9 keV isused as a source and HgI 2 as a detector Figure 9 illustrates the case ofexcitation with 109Cd with the energy =100 keV, and shows how the spectralook for three different detectors, the Hg1 2 detector (at room temperature),a Si(Li)-detector cooled to 77 K and a proportional counter (gas counter)at room temperature One sees that the HgI 2 detector nearly reaches theperformance of the much more clumsy, cooled Si(Li)-detector Still betterresolution has been obtained with the HgI 2 detector at room temperature,see for instance Fig 1 in ref 24a This work shows that it is nearly possibleto resolve the characteristic X-ray of fluorine at 680 eV The use of HgI 2

109collimator

~ ca 1 cm

sourceI

~I

Hg l, detector

Fig 7 Simple arrangement for material identification using X-ray fluorescence, XRF

sulphur

e 55

iii

Fig 8 XRF spectra from (a) sulphur, (b) chlorine and calcium, (c) BCR Basalt samplesusing 55Fe source and Hg1 2 detector [23]

Fig 9 Comparison of cryogenically cooled Si(Li), room temp HgI 2 and proportionalcounter for detecting lead spectrum using 109Cd excitation [ 231

described here corresponds to the special case where the radiation is ab-sorbed at a very shallow depth in the crystal, and it is therefore not neces-sary to collect the holes (see Section 3) A case where it has been possible toobtain such a good HgI2 crystal that hole collection is also sufficiently effec-tive is shown in Fig 10 [17] The higher energy 59 6 keV of the radiationhere means that it has a greater penetration depth, so that both electrons andholes must be collected in order to get good energy resolution We canremark here that the basic idea of using a high-Z material such as HgI 2 isthat it can absorb gamma rays more efficiently and/or absorb higher energyradiation. Such a detector requires considerably smaller volume than, forinstance a Ge-detector, which has lower Z .

(2) The photomultiplier in a scintillation detector may be replaced byanother type of photodetector, such as a semiconductor photo-detectorhaving sufficiently low noise, so that weak scintillation flashes can be de-tected HgI2 crystals were used with CsI(Tl) or BGO (bismuth germanate)scmtillators in such an application [25], see Fig 11 This gives us an oppor-tunity to make some basic comparisons between scintillation and `direct'

1 1 2

zzu

CHANNEL NUMBER

Fig 10 60 keV grays detected with a HgI2 detector having good hole collection, at threetemperatures [171

detectors The low-noise properties of Hg1 2 due to the small leakage currentsmay be used to advantage in the `scintillation counter' case, while the de-ficient hole collection, which gives bad resolution in normal Hg12 operationwhen high y energies are detected, is of no importance This is because the

JWZzaxU

NzZ

0U

4000

0

Backscatterpeak

~f

511 keV

Compton

edge

H9LFCsi(TI)

BBGo source

1 13

75

160CHANNEL NUMBER

Fig 11 511 keV annihilation y-rays from a 68Ga positron source taken with an Hg1 2photodetector coupled to a Csl(T1) scintillator crystal

scintillation light is absorbed in the very top layer of the HgI2 crystal, sothat only electron transport is utilized However, the line width is worsened,compared to what is expected for normal Hg! 2 operation when both elec-trons and holes can be collected Thus, the FWHM resolution for 511 keVenergy radiation is 10% when using CsI(Tl) and 19% when using BGO,which has a higher y absorption coefficient but also smaller efficiency ofconversion from particle energy to light The conversion efficiency forCsI(Tl) is ^'6% and for BGO -15%, so the expected numbers of -3 eVphotons are about 10 000 and 2000, respectively The numbers of generatedelectron-hole pairs in the HgI2 crystal are about the same, because thequantum detection efficiency is not very far from 1 [25] The statisticalspread is the square root of the above numbers, to obtain the FWHM valuesone has to multiply by a factor -2 35, which gives 2 4% and 5 3% (of 511keV) respectively This is considerably less than the observed 10% and 19%Much of the difference must be attributed to different light collection forirradiation impinging on different spots of the scintillator Improvementseems possible If one uses a photodetector with smaller quantum efficiency,e g , a P M tube with - 10% efficiency, the expected statistical spread islarger than in the above case (and corresponds more closely to the measuredresolution)

Direct detection of 511 keV radiation in Hg12 with perfect hole collec-tion and amplification would give a statistical spread of only 0 15%, assum-ing F = 0 27 [ 26] This corresponds to a FWHM value of 0 35% or 1 8 keVIt is rare to obtain Hgi2 crystals with reasonable hole collection, though Fig10 shows one case

The interest in direct detection of very high energy y-rays with HgI 2by using very large crystals (several cm') and the problems then caused bypoor hole collection has stimulated attempts to do away with the variationwith position of the collected charge from electron motion The variation

1 14

TEMPGRAD(AT)

(b)

RADIATION SHIELDS

HEAT LAMPS

SILICON WAFER

QUARTZ PINS

-WATER COOLED PLATE

(C)

HOT SURFACE

Fig 12 (a) 3 X 3 X ray detector array with continuous cylinder wall and central postsfabricated by thermomigrationof Al through a silicon wafer (b) Fabrication arrangement(c) Thermomigration process

was discussed in the context of Fig 3 This can be done by measuring theamplitude of the instantaneous current pulse rather than the collected charge[27] . As can be seen from the expression in Section 2 3, i(t) is proportionalto No

Still another method of avoiding the problems due to inefficient collec-tion of one type of carrier, usually the holes, is to choose an electrode con-

DIAMOND, BIAS VOLTAGE

482 k .V

CONVERSION ELECTRONS

FwMM a5 kaY

Pulstrr

FWNM 3BkaV

554 kaV 972 k<V1044 kaV

CHANNEL NUMBERFig 13 Conversion electrons from a 207Bi source detected with a diamond detector [30]

figuration (a hemispherical cathode and a central anode) such that the signaldue to hole motion, which is given by Ramo's theorem, is negligible com-pared with that due to the electrons [28]

(3) We have expanded m point (1) the advantage an exotic materialsuch as Hgl2 has for the detection of low-energy X-rays However, there arecases where the well-established technology and properties of silicon aremore important Figure 12 shows an X-ray array detector where an Alpattern deposited on one side of a Si wafer was made to thermo-migratethroughout its entire thickness (-'0 4 mm) by applying a thermal gradientacross the wafer, thus forming 9 rectangular `bins', where the centre postsserve as positive electrodes and collect the free electrons created by X-rays[29] Though the fabrication technique is not easy, variable `bin' sizes froma few tens of pm to several 100 µm can be made and an 55Fe X-ray linewidth < 500 eV can be obtained by cooling to 130 K The structure is usefulup to ^-20 keV

(4) Another illustration of the general discussion in Section 3 is offeredby the diamond detector Such a detector can work up to 600 °C because ithas hardly any generation current It is, for instance, suitable for detectionof the low-energy a-rays from tritium Another specific feature of this de-tector is that it becomes nearly insensitive to gamma radiation because ofthe low atomic number, Z = 6 Still another feature is that, because thethreshold energy for defect formation is relatively high in diamond (= 80 eV ),the detector has a resistance against radiation damage 103 times higherthan other `semiconductor detectors' One application is for measurementsin reactors An example of a spectrum taken with a diamond detector isshown in Fig 13 [30]

References

1 (a) K G McKay, Electron-hole production in germanium by alpha-particles, PhysRev, 84 (1951) 829 - 832(b) J W Mayer and B R Gossick, Use of Au-Ge broad area barrier as alpha-particlespectrometer , Rev Set Instr, 27 (1956) 407 - 408

200 Vats7

1 15

1 1 6

2 G Dearnaley and D C Northrop, Semiconductor Counters for Nuclear RadiationDetectors, E A F N Spon Ltd , London, 1966

3 G Bertolms and A Coche (eds ), Semiconductor Detectors, North-Holland Pub]Co , Amsterdam, 1968

4 G L Miller, A brief review of recent advances in compound semiconductors forradiation detectors, IEEE Trans Nucl Set , NS 19 (1) (1972) 251 - 259

5 F Shiraishi, M Hosoe and Y Takami, Totally depleted surface barrier detectors madeof ultra-high purity p-type silicon crystals, IEEE Trans Nucl Set, NS 29 (1) (1982)775- 778

6 C Kim, H Kim, A Yusa, S Miki, K Husimi, S Ohkawa and Y Fuchi, High resistiv-ity n-type silicon detectors produced by neutron transmutation doping, IEEE TransNucl Set, NS 26 (1) (1979) 292-296

7 E E Haller and F S Goulding, in T S Moss and C Hilsum (eds ), Handbook ofSemiconductors, North-Holland Pub] Co, Amsterdam, 1981, Vol 4, Ch 6, pp799 825

8 L S Darken Jr, R C Trammell, T W Raudorf and R H Pehl, Neutron damage inGe(HP) coaxial detectors, IEEE Trans Nucl Set, NS 28 (1) (1981) 572 578

9 G S Hubbard and E E Haller, The influence of material parameters on fast neutronradiation damage of high purity germanium detectors, IEEE Trans Nucl Set , NS 27(1) (1980) 235 - 239

10 P A Glasow, B Conrad, K Killig and W Lichtenberg, Aspects of semiconductorcurrent mode detectors for X-ray computed tomography, IEEE Trans Nucl Sci,NS 28 (1)(1981)563-571

11 C Scharager, P Siffert, A Holtzer and M Schieber, Performance comparison ofstandard CdTe and Hg1 2 detectors, IEEE Trans Nucl Set, NS-27 (1) (1980) 276-280

12 T Kobayashi, T Sugita, M Koyama and S Takayanagi, Performance of GaAs surface-barrier detectors made from high-purity gallium arsenide, IEEE Trans Nucl Set,NS 19 (3) (1972) 324 - 333

13 S Nishino, J A Powell and H A Will, Production of large-area single-crystal wafersof cubic SiC for semiconductor devices, Appl Phys Lett, 42 (5) (1983) 460 - 462

14 P A Tove, The role of contacts to nuclear radiation detectors, Nucl Instr Meth ,133 (1976) 445 - 452

15 M Hage-Ali, R Stuck, S Scharager and P Siffert, Correlation between surface pro-perties and detection characteristics of cadmium telluride detectors, IEEE TransNucl Set NS-26 (1) (1979) 281 291

16 J Kemmer, Fabrication of low noise silicon radiation detectors by the planar process,Nucl Instr Meth, 169 (1980) 499 - 502

17 M Slapa, A Harasiewiecz, W Seibt and P A Tove, Behaviour of Hg1 2 detectors atenvironmental temperature, Report INR 1884/SLDP/I/A, Inst of Nucl Res, Warsz-awa, 1980, pp 1 - 14

18 M Slaps, P A Tove and G Boberg, The characterization of CdTe and Hg1 2 crystalsand detectors by light spot scanning (LSS), Nucl Instr Meth , 150 (1978) 55 - 70

19 Z H Chu, M K Watt, M Slaps, P A Tove, M Schieber, T Davies, W Schnepple,P Randtke, R Carlaton and D Sarid, Characterization effort of HgI2 radiation de-tectors by pulsed laser transient charge injection techniques, IEEE Trans Nucl Set,NS 22 (1) (1975) 229 - 240

20 F Nave, C Canals, M Artuso, W Gatti, P S Manfredi and S F Kozlov, Transportproperties of natural diamond used as nuclear particle detector for a wide temper-ature range, IEEE Trans Nucl Set , NS-26 (1) (1979) 308 315

21 K Hecht, Zum Mechanismus des lichtelektrischen Primarstromes in isolierendenKristallen, Z Physik (Berlin), (1932) 235 - 245

22 P A Tove, Z H Cho and G Huth, The importance of the time scale in radiationdetection exemplified by comparing conventional and avalanche semiconductordetectors, Physica Scripta, 13 (1976) 83 - 92

1 1 7

23 M Singh, A J Dabrowski, G C Huth, J S Iwanczyk, B C Clark and A K Baird,X-ray fluorescence analysis at room temperature with an energy dispersive mercuryiodide spectrometer, Report on a contract DE-AS03-76-SF00113, pp 1-8

24 (a) A J Dabrowski, J S Iwanczyk, J B Barton, G C Huth, R Whited, C Ortale,T E Economou and A L Turkevich, Performance of room temperature mercuriciodide (HgI 2 ) detectors in the ultra low-energy X-ray region, IEEE Trans Nucl Sci,NS-28 (1) (1980) 536 - 540(b) J S Iwanczyk, J H Kusmiss, A J Dabrowski, J B Barton, G C Huth, T EEconomou and A L Turkevich, Room-temperature mercuric iodide spectrometryfor low-energy X-rays, Nucl Instr Meth , 193 (1982) 73 - 77

25 J S Iwanczyk, J B Barton, A J Dabrowski, J H Kusmiss and W M Szymczyk,A novel radiation detector consisting of an HgI2 photodetector coupled to a scm-tillator, Proc IEEE Nucl Sci Meeting, Oct 1982, IEEE Trans Nucl Sci, NS-30(1) (1983) 363 - 366

26 J S Iwanczyk, A J Dabrowski, G C Huth, A del Duca and W Schnepple, A studyof low-noise preamplifier systems for use with room temperature mercuric iodide(Hg12 ) X-ray detectors, IEEE Trans Nuct Sci, NS-28 (1) (1981) 579 - 582

27 A Beyerle, K Hull, B Lopez, J Markakis, C Ortale, W Schnepple and L van denBerg, Recent developments in thick mercuric iodide spectrometers, Proc IEEE NuctScs Meeting, Oct 1982, IEEE Trans Nucl Sci, NS 30 (1) (1983) 402 - 404

28 H L Malm, D Canali, J W Mayer, M A Nicolet, K R Zanio and W Akutagawa,Gamma-ray spectroscopy with single-carrier collection in high-resistivity semiconduc-tors, App! Phys Lett, 26 (6) (1975) 344 - 346

29 G E Alcora, K A Kost and F E Marshall, X-ray spectrometer by aluminiumthermomigration, IED 82, San Francisco, 13 16 Dec, 1982, Digest, pp 312 - 315

30 S F Kozlov, E Belcarz, M Hage-Ah, R Stuck and P Siffert, Diamond nuclear radia-tion detectors, Report CNR/PN 741 Laboratoire d'Electromque Nuclemre, Stras-bourg, pp 1 - 24

Biography

P A Tove was born in Sweden in 1924 and obtained a M S degreein Electrical Engineering from Chalmers University of Technology in 1947,and a Ph.D degree m Physics from the University of Uppsala in 1958 Hewas appointed professor in electronics at this university in the same yearHe has published some 80 papers m the field of radiation detectors, elec-tronic instrumentation, and on the physics of semiconductor devices, inparticular metal-semiconductor and silicide junctions