Question

Addition of arsenic in small amount to pure germanium will result in the formation of (a) \(\mathrm{n}\) -type semiconductor (b) germanium arsenide (c) p-type semiconductor (d) a superconducting alloy

Short answer

Addition of arsenic to pure germanium will result in the formation of an n-type semiconductor.

Step-by-step solution

Understanding Semiconductor Doping

Doping is the process of adding impurities to an intrinsic (pure) semiconductor to change its electrical properties. The type of impurity added determines the type of semiconductor formed.

Recognizing the Impurity Atom

Arsenic (As) is a group V element. When added to a group IV semiconductor like germanium (Ge), it will contribute extra electrons to the material.

Determining the Semiconductor Type

Since arsenic adds extra electrons, the doped semiconductor will have a surplus of negative charge carriers (electrons). This excess of electrons makes it an n-type semiconductor.

Key concepts

n-type Semiconductor

When we delve into the fascinating world of semiconductors, one term that often comes up is the n-type semiconductor. It's a type of material crucial in the electronics industry, mainly for its role in constructing various electronic components like diodes and transistors.

An n-type semiconductor is created through a process known as doping, which involves intentionally introducing impurities into an intrinsic, or pure, semiconductor. These impurities are typically atoms from group V of the periodic table, such as phosphorus, arsenic, or antimony. Unlike intrinsic semiconductors, which have four valence electrons, these atoms have five. When a group V element is introduced into the semiconductor lattice, four of its electrons form covalent bonds with the surrounding silicon or germanium atoms, but the fifth electron is extra and becomes a free charge carrier.

These additional electrons increase the semiconductor's conductivity significantly by providing more carriers for electric current. However, they do not create any additional positive charge; hence the material is 'n-type' for its negative charge carriers. The activity of these surplus electrons explains many of the electrical properties exhibited by n-type semiconductors.

Semiconductor Doping

Semiconductor doping is a precisely controlled process used to modify the electrical properties of semiconductors in order to meet specific technological needs. This process is akin to adding a pinch of salt to a dish to enhance its flavor; just as a chef carefully measures salt, engineers meticulously calculate the amount and type of impurity to add to the semiconductor.

Intrinsic semiconductors, which are chemically pure, hardly conduct electricity at all. By introducing a controlled amount of an impurity through doping, charge carriers are introduced, thereby increasing the semiconductor's conductivity. This is absolutely crucial for the semiconductor to be practically useful in electronic devices.

The impurity atoms introduced can create either an n-type or a p-type semiconductor, depending on whether they provide free electrons or create holes by accepting electrons. The interplay of these two types of doped semiconductors is used to create p-n junctions, the fundamental building blocks of most semiconductor devices.

Electrical Properties of Semiconductors

The electrical properties of semiconductors are what make them so versatile in electronic circuits. One of the hallmark properties is their conductivity, which can be precisely controlled through doping and is intermediate between that of a conductor and an insulator.

A key aspect of semiconductors is their energy band structure. This structure consists of a valence band filled with electrons and a conduction band where electrons can move freely to conduct electricity. The energy gap between these bands is called the band gap, which determines a semiconductor's electrical behavior. At room temperature, some electrons have enough energy to jump from the valence band to the conduction band, leading to electrical conductivity.

Doping influences this band structure by either adding free electrons (in n-type) or creating holes (in p-type), both of which can carry an electrical current. The amount and type of doping can tailor the electrical properties for specific applications, such as changing the conductivity or modifying the response of the semiconductor to light or heat. Understanding this intricate balance is fundamental for designing and using semiconductor-based devices effectively.