Semiconductor (solid state) detectors

Semiconductor (solid state) detectors Introduction Principle of semiconductors Silicon detectors, p-n junction, depleted region, induced charge energy measurement, germanium detectors position measurement, silicon strip detectors, pixel detectors silicon drift detectors 6. DEPFET 7. Photon detectors, APD, SiPM 8. 3D detectors Experimentální metody jaderné a subjaderné fyziky

1. Introduction Experimentální metody jaderné a subjaderné fyziky

Experimentální metody jaderné a subjaderné fyziky

Principle of semiconductors Experimentální metody jaderné a subjaderné fyziky

hole conduction Experimentální metody jaderné a subjaderné fyziky

- E - Experimentální metody jaderné a subjaderné fyziky

electron concentration g(E) - density of electron state in the conduction band f(E) ⦁ g( E) – electron concentration lowest energy level in the conduction band g() ≡ density of electron states in the lowest energy level approximation : f ≈ electron concentration in the lowest energy level hole concentration - density of hole state in the highest energy level of the valence band hole concentration in the highest energy level Boltzmann constant k ≈ 8.6 ⦁ eV⦁ E- Experimentální metody jaderné a subjaderné fyziky

= - Experimentální metody jaderné a subjaderné fyziky

= = μ mobility, E external electric field Current : J = e + = σ E, σ - conductivity R = 1/σ - resistivity Experimentální metody jaderné a subjaderné fyziky

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

3. Silicon semiconductors, p – n junction Si: Experimentální metody jaderné a subjaderné fyziky

n- type semiconductor Experimentální metody jaderné a subjaderné fyziky

p- type semiconductor Experimentální metody jaderné a subjaderné fyziky

Concentration of acceptors Concentration of donors Maxwell equations: Approximation of charge densities

Using resistivity of n-type R = 1/(e + ) in n-type, = 0 d= d= For R≈ 20 000d= 75 μm For reversed bias V= d ~ 300 μm R Experimentální metody jaderné a subjaderné fyziky

d d d d over-dopped p-type Experimentální metody jaderné a subjaderné fyziky

metal HV depletion region Ohmic contact : direct metal – p-type not possible, because of the barrier between metal and p-type instead heavily doped p-type and then a metal Experimentální metody jaderné a subjaderné fyziky

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

Induced charge at ( i.e. If x(t) =0 t ⟶ Experimentální metody jaderné a subjaderné fyziky

Ex. /pair a good preamplifier needed, low noice

DC direct coupling, AC Experimentální metody jaderné a subjaderné fyziky

4. Energy measurement • Construction of p-n junctions • Diffusedjunction 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 Experimentální metody jaderné a subjaderné fyziky

Compensating materialsdeveloped 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 100 000 Ω width of compensating region 10-15 mm Si(Li) , the noise is much greater then in normal Si cooling is needed Experimentální metody jaderné a subjaderné fyziky

Energy resolution Fluctuation of energy losses in the depleted region most probable energy loss Landau fluctuation Experimentální metody jaderné a subjaderné fyziky

Germanium detectors suitable for γ detection, Operation at low temperature, liquid nitrogen lithium compensated germanium Resolution at 1.33 MevGe detector 0.15 % NaI 8 % Experimentální metody jaderné a subjaderné fyziky

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 Experimentální metody jaderné a subjaderné fyziky

i) Experimentální metody jaderné a subjaderné fyziky

ii) R Experimentální metody jaderné a subjaderné fyziky

iii) Experimentální metody jaderné a subjaderné fyziky

Semiconductor (solid state) detectors