Which of the following accurately describes semiconductor diodes
a) Unlike junction diodes, point-contact diodes are enclosed in a suitable casing and have terminals for connecting them to a circuit.
b) Point-contact diodes are more likely to be used as rectifiers than junction diodes.
c) Unlike point-contact diodes, junction diodes utilize a point of metal wire in contact with a single wafer of P-type or N-type material.
d) Junction diodes are preferred over point-contact diodes for most purposes.
The answer is D.
Explanation:
Point contact diode:
The point contact diode is a type of diode that is made by forming a small area of contact by touching a metallic wire with an N-type semiconductor. This gives rise to the name “point contact diode.” These diodes have a faster switching speed than the traditional diodes that are typically used. These diodes are typically not recommended because of the low current ratings they offer and the poor reliability they offer.
P-N junction diode:
When two regions of opposing conductivity, N-type and P-type material, are joined together, a PN-junction is formed. This junction only allows current to travel in one direction, hence this kind of diode can only support that direction of current flow. The term “rectification” refers to the process by which alternating current is changed into direct current.
Semiconductor Basics
Semiconductors are materials with electrical properties that fall somewhere in the middle, between those of a “conductor” and those of a “insulator.” Examples of semiconductors include silicon (Si), germanium (Ge), and gallium arsenide (GaAs). They are poor conductors in addition to being poor insulators (hence their name “semi”-conductors). They have very few “free electrons” because the atoms that make up their structure are packed tightly together in a crystalline pattern that is referred to as a “crystal lattice,” but electrons are still able to flow through their structure, but only under specific conditions. It is possible to significantly improve the ability of semiconductors to conduct electricity by exchanging or adding specific donor or acceptor atoms to the crystalline structure of the material. This will result in the production of more free electrons than holes, or vice versa. This is accomplished by incorporating a minute quantity of a second element into the primary material, which can be silicon or germanium.
Both germanium and silicon are considered to be intrinsic semiconductors when considered on their own because they are chemically pure and contain no other components besides those that are semi-conductive. However, the conductivity of this intrinsic semiconductor material can be manipulated by carefully controlling the amount of impurities that are introduced into the material. To generate free electrons or holes, respectively, this intrinsic material can have various impurities, known as donors or acceptors, added to it. This process is called doping.
Doping refers to the process of adding donor or acceptor atoms to the atoms that make up a semiconductor. This process adds on the order of one impurity atom for every 10 million (or more) atoms that make up the semiconductor. Because the doped silicon is no longer pure, the donor and acceptor atoms are collectively referred to as “impurities.” If we dope the silicon material with a sufficient number of impurities, we can turn it into an N-type or P-type semi-conductor material. This is accomplished by doping the silicon material with a sufficient number of impurities.
The most common semiconductor fundamental material is silicon, by a wide margin. The four valence electrons in silicon’s outermost shell are shared with other silicon atoms to create complete orbitals, which have a total of eight electrons. Since each silicon atom shares an electron with its neighbor, the structure of the bond between the two silicon atoms makes the bond incredibly stable. Pure silicon (or germanium) crystals are good insulators or, at the very least, very high value resistors since there aren’t many free electrons available to travel around the silicon crystal. The lack of free electrons to traverse the silicon crystal is the cause of this. Crystalline solid structures are formed when atoms of a substance, such as silicon, are arranged in a particular symmetrical pattern. The term “intrinsic” is frequently used to refer to a crystal that is formed of pure silica, which is also referred to as silicon dioxide or glass.
However, in order to extract an electric current from a silicon crystal, it is not sufficient to merely connect the crystal to a battery supply. We must create a “positive” and a “negative” pole inside the silicon in order to achieve this. This will enable electrons, and consequently electric current, to flow away from the silicon. Doping the silicon with certain impurities results in the formation of these poles.
What is a semiconductor diode?
A diode that is composed of semiconductor material, most commonly silicon, is referred to as a semiconductor diode. It functions somewhat like a door through which electricity can flow, but unlike a door, it only opens in one direction. A diode is a device that is used to control the flow of electrical current so that only the desired direction is followed (the way the engineer wants them to). Electrical current can move through a material known as a semiconductor, but its speed is significantly slower than when it moves through a material such as copper, which is a stronger conductor. Most diodes in use today are semiconductor diodes. When referring to a semiconductor diode, the term “diode” is frequently used even though there is a more specific term.
N-type Semiconductor Basics
It is necessary for us to insert an impurity atom into the crystalline structure of our silicon crystal in order for it to be able to conduct electricity. Some examples of suitable impurity atoms include arsenic, antimony, and phosphorus (impurities are added). These impurities are commonly referred to as “pentavalent” impurities, and they are distinguished from other atoms by the fact that their outermost orbitals contain five electrons that can be shared with neighboring atoms. This makes it possible for four of the five orbital electrons to form bonds with the silicon atoms that are nearby, leaving one “free electron” that is able to move freely when a voltage is applied electrically (electron flow). In general, pentavalent atoms are referred to as “donors” due to the fact that each impurity atom “donates” one electron.
As a pentavalent additive to silicon, antimony (represented by the symbol Sb) and phosphorus (represented by the symbol P) are both frequently used. Antimony has a total of 51 electrons that are arranged in five shells around its nucleus, with the most distant orbital having a full complement of five electrons. The material that is produced as a consequence of semiconductor fundamentals having an excessive number of electrons that can carry current and that each have a negative charge is referred to as an N-type material. The “Majority Carriers” are the electrons, and the “Minority Carriers” are the holes that are created.
The electrons liberated from the silicon atoms by this stimulation are immediately replenished by the free electrons accessible from the doped antimony atoms when stimulated by an external power source. However, the doped crystal remains negatively charged due to the additional electron (the liberated electron) that is still floating around.
When a semiconductor material contains more electrons than holes, or when its donor density is higher than its acceptor density, it is classified as N-type, as shown. This results in a negative pole.
P-Type Semiconductor Basics
On the other hand, we introduce a “Trivalent” (3-electron) impurity into the crystalline structure, such as aluminium, boron, or indium, elements that only have three valence electrons available in their most outer orbital, then the formation of the fourth closed bond is prevented. Because of this, a complete connection cannot be made, and as a result, the structure of the crystal containing the semiconductor material has an abundance of positively charged carriers known as holes. These carriers are located in areas where electrons are absent.
Because there is now a gap in the silicon crystal, an electron in the surrounding area is drawn to it and will make an effort to move into the gap so that it can be filled. Nevertheless, as it moves, the electron that is filling the hole creates another hole behind it. To provide the impression that the holes are travelling as a positive charge through the crystal structure, this attracts another electron, which forms another hole behind it, which in turn attracts another electron, and so on (conventional current flow).
Because of this movement of holes, there is a deficiency of electrons in the silicon, which ultimately results in the transformation of the entire doped crystal into a positive pole. Trivalent impurities are commonly referred to as “Acceptors,” because they are constantly “accepting” extra or free electrons despite the fact that each impurity atom produces a hole in the material. Boron, denoted by the symbol B, is frequently utilised as a trivalent additive due to the fact that it possesses only five electrons, which are arranged in three shells around its nucleus, with the outermost orbital containing only three electrons. The doping of atoms with boron results in conduction that is composed primarily of positive charge carriers, producing a P-type material. The positive holes in the material are referred to as the “Majority Carriers,” while the free electrons are referred to as the “Minority Carriers.” When the acceptor density of a semiconductor basics material reaches a certain threshold, the material is classified as P-type.
References
https://answerswallet.com/which-of-the-following-accurately-describes-semiconductor-diodes-pxry/
Semiconductor diode Definition & Meaning | Dictionary.com
Semiconductor Basics & Semiconductor Physics Tutorial (electronics-tutorials.ws)