Semiconductor Electronics: Basics and Devices

The primary difference lies in the energy gap between the valence and conduction bands. In conductors, these bands either overlap or are partially filled, allowing electrons to move freely and achieve high conductivity. Semiconductors, however, have a smaller energy gap, requiring less energy for electrons to transition to the conduction band, leading to a moderate level of conductivity.

The valence band represents the energy levels occupied by valence electrons, typically involved in bonding within the semiconductor. The conduction band, on the other hand, represents the energy levels where electrons can freely move and contribute to electrical conductivity. The energy gap is the energy difference between the top of the valence band and the bottom of the conduction band. This gap determines how easily electrons can move into the conduction band, dictating the semiconductor's conductivity.

In a solid, individual atoms come close together, causing their electron energy levels to interact. This interaction leads to the splitting of these energy levels, forming a range of closely spaced energy levels called energy bands. Conductors have overlapping or partially filled valence and conduction bands, enabling electrons to move freely and achieve high conductivity. Semiconductors exhibit a small energy gap between these bands, allowing for modest conductivity that can be controlled. Insulators, however, have a large energy gap, preventing electrons from easily transitioning to the conduction band, resulting in very low conductivity.

<p>An intrinsic semiconductor is a pure semiconductor material with no impurities added. It exhibits poor conductivity at absolute zero temperature but its conductivity can be increased by raising the temperature.</p> Signup and view all the answers

<p>N-type semiconductors are created by doping a pure semiconductor with impurities that have more valence electrons than the host semiconductor, like phosphorus. This results in an excess of free electrons, making electrons the majority carriers and holes the minority carriers. In contrast, p-type semiconductors are formed by doping with impurities that have fewer valence electrons than the host material, such as boron. This creates an excess of holes, making them the majority carriers and electrons the minority carriers.</p> Signup and view all the answers

<p>A p-n junction diode consists of a p-type semiconductor joined to an n-type semiconductor. Under forward bias, a positive voltage is applied to the p-side and a negative voltage to the n-side. This reduces the depletion region width and increases the current flow. Under reverse bias, the negative voltage is applied to the p-side and the positive voltage to the n-side. This widens the depletion region and reduces the current flow, typically resulting in a very small leakage current. The I-V characteristics show a sharp increase in current under forward bias and a negligible current under reverse bias. These characteristics are essential for its use as a rectifier.</p> Signup and view all the answers

<p>Electrons are majority carriers and pentavalent atoms are the dopants.</p> Signup and view all the answers

<p>Holes are majority carriers and trivalent atoms are the dopants.</p> Signup and view all the answers

<p>(Eg)c &gt; (Eg)Si &gt; (Eg)Ge</p> Signup and view all the answers

<p>All of the above.</p> Signup and view all the answers

<p>Lowers the potential barrier.</p> Signup and view all the answers

<p>The energy gap, or band gap, is the energy difference between the valence band and the conduction band in a material. In an insulator, this gap is large, preventing electrons from easily transitioning to the conduction band, resulting in very low conductivity. Semiconductors, on the other hand, have a smaller energy gap, allowing for a moderate level of conductivity. In essence, the size of the energy gap dictates the material's conductivity, classifying it as an insulator, semiconductor, or conductor.</p> Signup and view all the answers

<p>An intrinsic semiconductor is a pure semiconductor material with no added impurities. It exhibits poor conductivity at room temperature. Extrinsic semiconductors, on the other hand, are created by intentionally adding impurities (dopants) to a pure semiconductor, which alters its conductivity. This intentional doping allows for control over the material's electrical properties, making it useful for various electronic applications.</p> Signup and view all the answers

<p>(i) For n-type semiconductors, a common dopant for germanium is arsenic (As), which has five valence electrons, contributing to an excess of free electrons in the material. (ii) For p-type semiconductors, a common dopant for germanium is boron (B), which has three valence electrons, creating a deficiency of electrons (or an excess of holes) in the material.</p> Signup and view all the answers

<p>(i) The depletion region in a p-n junction is a thin region near the interface where mobile charge carriers (electrons and holes) are depleted due to diffusion. This region is characterized by immobile ions, creating an electric field that opposes further diffusion of charge carriers. (ii) The barrier potential is the potential difference across the depletion region, which acts as an electrostatic barrier, preventing the free flow of charge carriers across the junction in equilibrium. It is a crucial factor in determining the diode's forward and reverse bias characteristics.</p> Signup and view all the answers

<p>(i) Diffusion current in a p-n junction is the movement of charge carriers across the junction due to concentration differences, driven by the tendency of the system to reach equilibrium. (ii) Drift current is the movement of charge carriers under the influence of an electric field. This current is caused by the force exerted on the charge carriers by the electric field, which directs their movement towards the opposite polarity.</p> Signup and view all the answers

<p>A rectifier is a device that converts alternating current (AC) into direct current (DC). This conversion is achieved through the use of diodes, which allow current flow in only one direction. The key property of diodes used for rectification is their ability to conduct current easily in the forward bias direction and almost block current flow in the reverse bias direction. This &quot;one-way valve&quot; behavior of diodes enables the rectification process.</p> Signup and view all the answers

<p>Rectification is the process of converting alternating current (AC) into direct current (DC). A half-wave rectifier utilizes a single diode to achieve this conversion. During the positive half-cycle of the AC input, the diode is forward-biased and conducts, allowing current to flow through the load resistor. During the negative half-cycle, the diode is reverse-biased and blocks current flow. The output waveform is a pulsating DC signal with only the positive half-cycles of the AC input present. The circuit diagram shows a diode connected in series with a load resistor and an AC voltage source. The input waveform is sinusoidal, and the output waveform follows the positive half-cycles of the input, resulting in unidirectional DC output.</p> Signup and view all the answers

<p>An n-type semiconductor is formed by doping a pure semiconductor with a pentavalent impurity, such as phosphorus or arsenic. These impurities have five valence electrons, donating one extra electron to the crystal lattice. This extra electron becomes a free charge carrier, increasing the semiconductor's conductivity. Since electrons are the majority carriers in this case, the n-type semiconductor exhibits a higher concentration of free electrons compared to holes. The energy band diagram shows the conduction band partially filled due to the presence of these free electrons, and the energy gap is smaller compared to insulators. The donor energy level (ED) is located just below the conduction band, representing the energy level of the extra electrons contributed by the dopants.</p> Signup and view all the answers

<p>An intrinsic semiconductor is a pure semiconductor material with no intentional impurities added. It exhibits poor conductivity at room temperature. In the case of silicon (Si), each silicon atom forms four covalent bonds with its neighboring silicon atoms, sharing its four valence electrons to achieve stability. Now, imagine that one of these valence electrons gains enough energy to break free from its covalent bond and escape into the crystal lattice. This leaves behind a vacancy or a &quot;hole&quot; in the covalent bond structure. This hole effectively acts as a positive charge carrier, as the absence of an electron creates a region with a net positive charge. The formation of a hole is essential for understanding the electrical conductivity of semiconductors, as these holes contribute to the overall current flow.</p> Signup and view all the answers