Semiconductor (solid state) detectors

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Daniela Navrátilová
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1 1. Introduction Semiconductor (solid state) 2. Principle of semiconductors detectors 3. Silicon detectors, p-n junction, depleted region, induced charge 4. energy measurement, germanium detectors 5. position measurement, silicon strip detectors, pixel detectors silicon drift detectors 6. DEPFET 7. Photon detectors, APD, SiPM 8. 3D detectors 1

2 1. Introduction 2

3 3

4 4

5 5

6 Principle of semiconductors 6

7 hole conduction 7

8 8

9 - E - E f k ~8.6 x 10 5 ev T 1 9

10 electron concentration g(e) - density of electron state in the conduction band f(e) g( E) electron concentration E c lowest energy level in the conduction band g(e c ) N c density of electron states in the lowest energy level approximation : f e ( E E f)/kt Boltzmann constant k ev K 1 E-E f 1 ev electron concentration in the lowest energy level n e = N c e E c E f kt hole concentration E V highest energy level in the valence band N V - density of hole state in the highest energy level of the valence band hole concentration in the highest energy level n h = N V e E f E v kt 10

11 E g = E c - E V 11

12 v e = μ e E v h = μ h E μ mobility, E external electric field Current : J = e n i (μ e + μ h ) E = σ E, σ - conductivity R = 1/σ - resistivity μ e μ h 12

13 Recombination and trapping of the charge carriers i) Direct recombination ii) Recombination resulting from impurities in the crystal a) b) iii) Trapping resulting from impurities in the crystal iv) Structural defects in the lattice 13

14 3. Silicon semiconductors, p n junction Si: 14

15 15

16 n- type semiconductor 16

17 17

18 p- type semiconductor 18

19 19

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23 23

24 Concentration of acceptors N A Concentration of donors N D Approximation of charge densities Maxwell equations: 24

25 25

26 Using resistivity R n of n-type d= 2 ε R n μ e V 0 R = 1/(e n i (μ e + μ h ) ) in n-type, μ h = 0 n i = N D d= 2 ε R p μ h V 0 R R n R p V 0 For R Ω, V 0 = 1 V d= 75 μm For reversed bias V= V 0 + V B ~ V d ~ 300 μm 26

27 d d d d p + over-dopped p-type 27

28 28

29 metal depletion region HV Ohmic contact : direct metal p-type not possible, because of the barrier between metal and p-type instead heavily doped p-type p + on the p type substrade and then a metal 29

30 Induced charge d - thickness of the depletion region Q - charge in the depletion region page 25: but different coordinate frame, zero at the junction x x - x p, x p d, E=-dV/dx,resistivity R=1/( ) τ = ε R t d 30

31 Induced charge at t d q e (t d ) = i.e. If x(t) =0 q h t = t q h = 31

32 Ex. /pair a good preamplifier needed, low noice 32

33 DC direct coupling, AC 33

34 4. Energy measurement Construction of p-n junctions Diffused junction diode: diffusion of donors to p-type at the temperature 1000 C Surface barrier junction: junction between a semiconductor and a metal n-type Si with Au, p-type Si with Al sensitive to light Ion-implanted junctions: a substrate is bombarded by ions from an accelerator Depleted region small energy measurement for low energies 34

35 Guard ring 35

36 in Si particle energy ( MeV) 36

37 Compensating materials developed to increase the depletion region by lithium drifting process known as p-i-n junction Li diffused to p-type, a narrow n-type is created electrons drifted to p-type, negative space charge application of HV positive Li ions drifted to p-type for sufficient time to create the same concentration of positive ions and electrons t no space charge, i.e. compensated region resistivity up to Ω width of compensating region mm Si(Li), the noise is much greater then in normal Si cooling is needed 37

38 Energy resolution Fluctuation of energy losses in the depleted region, ΔE m.p. most probable energy loss Landau fluctuation 38

39 - Germanium detectors suitable for γ detection, - High purity germanium (PHGe), depletion region~ cm, low temperature during - measurement only Resolution at 1.33 Mev Ge detector 0.15 % NaI 8 % 39

40 Shape of Ge detectors - planar, circular shape, diameter 1-2 cm, volume cm 3 coaxial, volume up to 400 cm 3 40

41 5. Position measurement, silicon strip and pixel detectors i) Manufacturing of Si strip detectors ii) Microstrip detectors iii) Position resolution iv) Pixel detectors v) Silicon drift detectors 41

42 i) 42

43 43

44 44

45 ii) R 45

46 46

47 47

48 48

49 iii) 49

50 50

51 51

52 analog readout 52

53 iv) 53

54 Advantages and disadvantages 54

55 55

56 56

57 v) 57

58 58

59 59

60 Application of strip, pixel and pad detectors Trackers: precise determination of particle tracks (strips or pixels) Vertex detectors: in collider experiments, detectors situated around the interaction vertex Topology: sensors mounted on a planar carbon frames or cylindrical carbon frames Calorimeters: as active layers in sampling calorimeters 60

61 forward and backward silicon tracker of the H1 experiment Collider HERA, DESY Hamburg, electrons (~26 GeV) vs protons (920 GeV) several layers of circular planes equipted with strip sensors Si sensors particle protons Beam pipe electronics Emitted particle Interaction vertex electrons 61

active layers from Si wafers electronic layer above active layer Si wafers 6

62 Pad silicon detectors for the readout of the electromagnetic calorimeter CALICE (calorimeter for linear collider) calorimeter: absorber tungsten, active layers from Si wafers electronic layer above active layer Si wafers 6 x 6 cm, 1 pad 1x1 cm, depletion region Si 500 μm readout board W - layer Si wafers 62

63 5. DEPFET Bipolární tranzistor: Nepřipojený k obvodu Připojený k obvodu emitor báze kolektor 63

FET tranzistor Polem řízené (neboli unipolární či FET) tranzistory spínají/omezují protékající proud na základě toho, jaké napětí je na drain Tři jednotky FETu:

64 FET tranzistor Polem řízené (neboli unipolární či FET) tranzistory spínají/omezují protékající proud na základě toho, jaké napětí je na drain Tři jednotky FETu: řídicí se nazývá gate a značí se "G", spínaný proud vstupuje do drainu "D" a vystupuje z source "S". drain je zde jako kolektor, source jako emitor a gate jako báze 64

65 FET Proud teče mezi S a D mezi nimiž je napětí. Napětí na D mění vodivost substrátu, tj proud teče/neteče Zdroj proudu je S, výstupní proud je v D. 65

66 DEPFET je FET vytvořený na plně vyčerpanén substrátu. Působí současně jako senzor a zesilovač 66

67 Top gate n + n-si P channel FET on a fully depleted n-bulk 67

68 electrons from photon are collected at the internal gate the energy deposited by a photon is determined by the change of the FET conductivity 68

69 This difference ~to the total amount of collected charge clear mode - change of the FET conductivity, 69

70 7. Semiconductor photon detectors APD - avalanche photodiode replace e.g. photomultipliers in calorimeters, very small devices, can be connected with fibers Usual photodiode PD 70

71 avalanche photodiode 71

72 72

73 HAPD - hybrid APD 73

74 SiPM Silicon Photon Multipliers 1156 photodiodes on the area 1.1 x 1.1 mm 2 depletion region 74

75 SiPM detects individual photons, current ~ to the number of fired pixels 75

76 SiPM were first developed for the readout of scintillation light of the hadron calorimeter within CALICE collaboration Hadron calorimeter WLS fibre Scintillation light from the tile is collected by a WLS fiber which is directly connected to a SIPM. 76

77 (pixel photodiode) Pedestal noise 77

78 3D detectors 78

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