![]() In the analysis of BJT under an X-ray beam, in addition to its operation as a sensor to measure the dose or some diagnostic X-ray tube parameter, it has also led to technological innovation in the technique of digital data storage based on the effect of radiation.ġ.1. In electronics, the BJT is used as a current amplifier, and depending on the bias and point of view it also becomes a voltage amplifier. Even knowing that the most complete theory to describe the “transistor effect” is based on quantum theory (the energy band theory of solids), here it is preferable to take a simpler experimental approach to clearly understand the operation of the BJT. Therefore, it addresses some topics such as the structure of the device, the bias configuration when operating in active mode, and so on. In this article an overview on the BJT and its principle of operation were made for the purpose of better understanding how such a semiconductor device behaves when under diagnostic X-ray beam. These free electrons which are available in minute quantity also carry a little amount of current in the p-type semiconductors.Although not manufactured to be used under X-ray photons, the commercial bipolar junction transistor (BJT) is an electronic device that can be used as an ionizing radiation sensor. The mobility of holes is poor as they are more bound to the nucleus.Įven at the room temperature, the electron-hole pairs are formed. The electrons available in the conduction band of the n-type semiconductor are much more movable than holes available in the valence band in a p-type semiconductor. The conductivity of an n-type semiconductor is nearly double to that of p-type semiconductor. In a p-type conductivity, the valence electrons move from one covalent to another. As the current flow through the crystal is by holes, which are carriers of positive charge, therefore, this type of conductivity is known as positive or p-type conductivity. The holes are available in the valence band are directed towards the negative terminal. ![]() When a potential difference is applied across this type of semiconductor as shown in the figure below: In a p-type semiconductor, a large number of holes are created by the trivalent impurity. The word “p” stands for positive material. It is because of the predominance of holes over electrons that the material is called as a p-type semiconductor. ![]() But the holes are more in number as compared to the electrons in the conduction band. They are produced when thermal energy at room temperature is imparted to the germanium crystal-forming electron-hole pairs. A small or minute quantity of free electrons is also available in the conduction band. The energy band diagram of a p-type Semiconductor is shown below:Ī large number of holes or vacant space in the covalent bond is created in the crystal with the addition of the trivalent impurity. Thus, each gallium atom provides one hole in the germanium crystal.Īs an extremely small amount of Gallium impurity has a large number of atoms, therefore, it provides millions of holes in the semiconductor.Įnergy Band Diagram of p-Type Semiconductor This missing electron is known as a Hole. Hence, the fourth covalent bond is incomplete, having one electron short. In the fourth covalent bonds, only the germanium atom contributes one valence electron, while gallium atom has no valence bonds. ![]() Each atom of the impurity fits in the germanium crystal in such a way that its three valence electrons form covalent bonds with the three surrounding germanium atoms as shown in the figure below: Conduction Through p-Type SemiconductorĪ trivalent impurity like gallium, having three valence electrons is added to germanium crystal in a small amount.Energy Band Diagram of p-Type Semiconductor.Such types of impurities which produce p-type semiconductor are known as an Acceptor Impurities because each atom of them create one hole which can accept one electron. ![]()
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