Anzivino et al., NIM A430 (1999) 100) Advances in APD's Y.MusienkoĮxcellent photosensor: Large area High QE and gain Good uniformity over the sensitive area Low excess noise factor Low voltage and temperature sensitivity But: High operating voltage (~2000 V) High sensitivity to heavily ionizing particles Structure should be sensitive to hadron irradiation Difficult for mass production High price “Beveled edge” APD’s summary Advances in APD's Y.Musienko bias voltage before and after lethal a-particles damage (From G. These abnormal events were probably triggered by rare but highly ionizing nuclear collision events Pulse height spectra of APD response to a-particles at different bias voltages: U=1000 V, M=1.2 U=1500 V, M=2 U=1650 V, M=4 U=1700 V, M=5 U=1750 V, M=6 APD leakage current vs. “Beveled edge” APDs in HEP environment When operating these APDs at high gain in beam line environment, abnormal behavior and eventually permanent damage to the detectors were observed. Moszynski et al., NIM A497 (2003) 226) Advances in APD's Y.Musienko Solovov et al., NIM A488 (2002) 572) Energy spectrum of 662 keV g-rays measured with CsI(Tl) and YAP:Ce crystals (M. Low excess noise factor (measured by Advanced Photonix, Inc.) Advances in APD's Y.MusienkoĪPI APD – Scintillation Light Detection Pulse height spectrum of scintillation due to 5.5 MeV a-particles in liquid Xe (l=178 nm), measured at T=-102 C and M=120 (V.N.Farrell et al., NIM A353 (1994) 176 Advances in APD's Y.Musienko (from M.Moszynski et al., NIM A485 (2002) 504) Advances in APD's Y.Musienkoĭeep-diffused “beveled edge” APD (RMD) Gain ~104 possible Low energy gamma detection (~200eV threshold) R. Schematic cross-section and electric field profile, according to Advanced Photonix Inc. The APD edge (perpendicular to the junction) is beveled in order to reduce the field along the device edge, enabling the device to sustain the high biases necessary for APD operation. The broad gain region enables device operation at high gain with low excess noise and excellent gain uniformity. “Beveled edge” APD (API) It is made by growing the p-type epitaxial layer on n-type neutron transmutation doped silicon. In the CMS ECAL : - high radiation levels - 4T magnetic field - limited space - PbWO4 (low light yield, 420-450 nm emission peak) Photodetector must be : - radiation hard - operational in high magnetic field - small nuclear counter effect and reasonable gain - small excess noise factor - match the properties of PbWO4 light (high QE, high speed) - low sensitivity of the gain on temperature and voltage - high reliability (10 years of LHC) and low price !!! PIN photodiode has no gain and has high “nuclear counter effect” Avalanche Photo Diode APDs from several producers had been considered Photo Detector Requirements Advances in APD's Y.Musienko
Low light yield Advances in APD's Y.Musienko.ED-13 (1972) 164) Ionization coefficients as a function of electric field in silicon Advances in APD's Y.MusienkoĪPDs are used in telecommunications > 30 years To be used in HEP they should satisfy certain requirements Requirements depend on the application Applications: Calorimetry SciFi trackers Cherenkov light detection TOF … APD’s for supercolliders Here I will discuss mainly the applications of the APDs for HEP calorimetry CMS ECAL is a good example Advances in APD's Y.Musienkoģ Density 8.28 8.9 Rad length, X 0 Interaction length 224 Molière radius 21.9 Decay time 5 (39%) 15 (60%) 100 (1%) Refractive index 2.30 Max emission 425 Light yield ~50 Temp coeff -2 Lead Tungstate Properties Silicon is a good material for APD construction: high sensitivity in visible and UV range, significant difference between ionization coefficients for electrons and holes – smaller positive feedback and smaller multiplication noise Excess Noise Factor: F=k*M+(1-k)(2-1/M) k=b/a (k-factor) b- ionization coefficient for holes a- ionization coefficient for electrons (see R.J. With increasing reverse bias voltage, electrons (or holes) are accelerated and can create additional electron-hole pairs through impact ionization. Musienko* Northeastern University, Boston & CMS ECAL collaboration *On leave from INR(Moscow)Īvalanche multiplication APD’s for supercollider - requirements Different APD structures APDs for the CMS ECAL Radiation hardness and reliability APDs at low temperatures New APD developments Conclusion Outline Advances in APD's Y.MusienkoĪvalanche multiplication Avalanche photodiodes are photodiodes with built-in high electric field region.