A study of signal generation and charge collection in a-Si:H diodes for radiation imaging

Technical Report · Mon Oct 01 04:00:00 EDT 1990

DOI:https://doi.org/10.2172/5632939· OSTI ID:5632939

Fujieda, I

Its high radiation resistivity and large-area capability are the expected advantages of this material together with its ability to provide a front-end readout electronics in the vicinity of the sensor element. Electrons and holes created by incoming charged particles, X-rays, {gamma} rays, are drifted by the electric field inside a-Si:H diodes and this carrier movement induces signal charges on electrodes. Charge collection and signal generation process are analyzed in terms of carrier mobilities, lifetimes and electric field. Charge collection in thick a-Si:H diodes is often limited by deep-level trapping of carriers during transit and a finite charge integration time required for single particle counting in some applications and sometimes by volume recombination of carriers for detecting heavily-ionizing particles such as {alpha} particles. The charge collection process is also strongly affected by the non-uniform electric field profiles in a-Si:H diodes caused by the fixed space charges inside the material under reverse-bias. Signal generation due to a weak light pulse irradiating each end of a thick diode is measured as a function of a reverse-bias and it gives a valuable information about the fixed space charges. Field profiles can be manipulated by either doping, electrode geometry, or combination of both to improve the charge collection process. One can apply a higher reverse-bias on a diode with an equivalent thickness by providing buffer layers at each end of the diode and thus suppressing soft breakdown phenomena. X-ray detection with a good sensitivity is demonstrated by an a-Si:H photodiode coupled to an evaporated CsI scintillator. The scintillation quality of evaporated CsI layers can be made almost identical to its single crystal counterpart. Fields of a-Si:H radiation detector application include high energy physics, medical imaging, materials science and life science. 78 refs., 68 figs., 11 tabs.

• Research Organization: Lawrence Berkeley Lab., CA (USA)
• Sponsoring Organization: DOE; USDOE, Washington, DC (USA)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 5632939
• Report Number(s): LBL-30291; ON: DE91010243
• Country of Publication: United States
• Language: English

Related Subjects

440100* -- Radiation Instrumentation
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
AMORPHOUS STATE
CARRIER LIFETIME
CARRIER MOBILITY
CHARGE COLLECTION
DETECTION
ELECTRIC FIELDS
ELECTRODES
ELEMENTS
HIGH ENERGY PHYSICS
LIFETIME
MATERIALS
MEASURING INSTRUMENTS
MOBILITY
PHYSICS
RADIATION DETECTION
RADIATION DETECTORS
READOUT SYSTEMS
SCINTILLATION COUNTERS
SCINTILLATOR-PHOTODIODE DETECTORS
SEMICONDUCTOR DETECTORS
SEMICONDUCTOR DEVICES
SEMICONDUCTOR DIODES
SEMICONDUCTOR MATERIALS
SEMIMETALS
SI SEMICONDUCTOR DETECTORS
SIGNALS
SILICON
SPACE CHARGE
TRAPPING
USES
X-RAY DETECTION