Questions about Silicon Diode Detectors

In summary, a silicon diode can be used as an ionizing radiation measurement instrument in both non-biased and reverse-biased modes. In non-biased mode, the built-in potential allows for measurement of charge through the connection to an electrometer. In reverse-biased mode, the depletion zone widens, creating a high resistance to the flow of charge carriers and allowing for minimal electric current to cross the p-n junction. This prolongs the life of the diode and can improve detection efficiency and signal-to-noise ratio. The type of diode (p-type or n-type) does not affect the migration of electrons to the n-side, but p-type diodes are often preferred for radiation measurement. It is also
  • #1
CL39
9
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I have some questions about how silicon diode works, specifically as a ionizing radiation measurement instrument. I will write what my understanding is so far from different textbooks/websites (please comment whether I have it correct) and also write question where I get confused. Thank you.


- For radiation measurement, can be used in non-biased and reverse-biased mode.

CONSTRUCTION:

- When p-type silicon and n-type silicon come into contact

The majority carrier (hole) of p-side diffuse to n-side, leaving negatively-charged acceptor ion.

The majority carrier (e-) of n-side diffuse to n-side, leaving positively-charged donor ion (the minority carrier).

This forms the space charge region or depletion layer, with built-in potential (positively charged on the n-side and negatively charged on the p-side).

This built-in potential prevents any further movement of majority carriers.

The space charge region is a zone with a net charge provided by the fixed ions (donors or acceptors) that have been left uncovered by majority carrier diffusion

There are two types of p-n junction diode detectors, p-type diode (made with p-type silicon substrate doped with small amount of n-type silicon) and n-type diode (made with n-type silicon substrate doped with small amount of p-type silicon)


- For radiation measurement, can be used in non-biased and reverse-biased mode.

FOR OPERATION IN NON-BIAS MODE

- Due to the built-in potential, electrons from the electron-hole pair (created in the depletion zone by ionizing radiation) moves to the n-side, where the connection to the electrometer allows measurement of charge

FOR OPERATION IN REVERSE-BIAS MODE
- Because the p-type material is now connected to the negative terminal of the power supply, the 'holes' in the P-type material are pulled away from the junction, causing the width of the depletion zone to increase. Similarly, because the N-type region is connected to the positive terminal, the electrons will also be pulled away from the junction. Therefore the depletion region widens, and does so increasingly with increasing reverse-bias voltage. This increases the voltage barrier causing a high resistance to the flow of charge carriers thus allowing minimal electric current to cross the p–n junction.

When ionizing radiation creates electron-hole pairs in the depletion zone, the electrons are swept to the n-side by the positive external potential on the n-side and the charges are collected by the electrometer.


QUESTIONS

- in reverse-bias mode, “there is no current, except some leakage”. But isn’t this also true for non-bias mode (once equilibrium is established, there’s no more migration, isn’t it?)

- Between p-type diode detector (with p-type silicon substrate doped with small amount of n-type silicon) and n-type diode detector (with n-type silicon substrate doped with small amount of p-type silicon), why is p-type detector better for collecting electrons at the n-side. Wouldn’t electrons (liberated by ionizing radiation migrate to the n-side in p-type or n-type just the same? I believe most radiation measurement diodes are p-type.

- I read that p-type diode suffers less damage over time than n-type, why is this true?

- why does operating in reverse-bias mode prolong the life of diode (as compared to non-biased mode)?

- what is the significance of the increased width of the depletion zone in reverse-bias mode? Does it give you better detection efficiency? Better signal to noise ratio?
 
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  • #2
CL39 said:
in reverse-bias mode, “there is no current, except some leakage”. But isn’t this also true for non-bias mode (once equilibrium is established, there’s no more migration, isn’t it?)
Yes, that's also true.

It is difficult to reply without links to the sources of the assertions you are asking about.
 

1. What is a silicon diode detector and how does it work?

A silicon diode detector is a type of radiation detector that is commonly used in scientific research and medical imaging. It operates by converting incoming radiation, such as X-rays or gamma rays, into electrical signals that can be measured and analyzed.

2. What are the main advantages of using silicon diode detectors?

Silicon diode detectors have several advantages, including high sensitivity, fast response time, and a wide dynamic range. They are also relatively inexpensive and can be easily mass-produced.

3. How accurate are silicon diode detectors in measuring radiation?

Silicon diode detectors are highly accurate and precise in measuring radiation. They have a linear response to radiation, meaning that the electrical signal produced is directly proportional to the amount of incoming radiation. This makes them ideal for quantitative measurements.

4. Can silicon diode detectors be used for different types of radiation?

Yes, silicon diode detectors can be used to detect a wide range of radiation types, including X-rays, gamma rays, and charged particles such as electrons and protons. This versatility makes them a popular choice for various scientific and medical applications.

5. How do silicon diode detectors differ from other types of radiation detectors?

Compared to other types of radiation detectors, such as scintillation detectors or Geiger-Müller counters, silicon diode detectors offer better energy resolution and can operate at lower voltages. They also have a more compact size and can be easily integrated into electronic systems.

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