Band Structure In Quantum Wells

In order to interpret correctly the optical absorption experiments in quantum wells, we need to know the band structure. Figure 8.2 of Chapter 8 shows the absorption spectra of a 40 period multiple quantum well (MQW) GaAs-AlGaAs, in which the barriers have a width of 7.6nm 3 . Observe that the spectrum follows in general the steps of the DOS curve in 2D semiconductors (Section 4.2). At the edge of each step there is a sharp maximum that, as will be shown in the next section, is attributed to...

Lattice Vibrations

In this section we pretend to give a short review of vibrations in periodic systems such as crystals. The adiabatic approximation in solid state physics allows the separate study of those properties of materials, attributed to electrons, like the electrical conductivity, and those which depend on the vibrations of the atoms, such as the thermal properties. Suppose a mechanical wave, or a sound wave, travelling through a solid. If its wavelength X is much larger than the lattice constant of the...

Basic Properties Of Twodimensional Semiconductor Nanostructures

One of the most practical two-dimensional semiconductor structures consists of a sandwich of gallium arsenide (GaAs), with a thickness in the nanometre range, surrounded on each side by a semiconductor such as aluminium gallium arsenide (Alx Ga1-xAs) of higher bandgap. The bandgap of AlxGa1-xAs (x 0.3) is close to 2.0 eV while that of GaAs is 1.4 eV. As a consequence, the potential energy profile has the shape of a square well (Figure 4.1(a)), with a barrier height of 0.4 eV for electrons and...

Quantum Transport In Nanostructures

Next we are going to deal with quantum transport, which is produced when nanostructures are connected to an external current by means of leads or contacts. This transport is also called mesoscopic transport. As we explained in Section 1.3, the term mesoscopic refers to systems with a range of sizes between the macroscopic world and the microscopic or atomic one, and which have to be explained by quantum mechanics. These systems in electronics are also known as submicron or nanoscale devices....

Perpendicular Transport

In this section, we study the motion of the carriers perpendicularly to the planes of the potential barriers separating quantum heterostructures. This kind of transport is often associated to quantum transmission or tunnelling, since the carriers do not need to have enough energy to surmount the barriers. When a particle goes through a potential barrier, the wave function and its derivative in the perpendicular direction must be continuous, which leads to transmitted and reflected wave...

Mosfet Structures

The main contribution to present technology in general, and microelectronics in particular, is probably the metal-oxide-semiconductor field-effect-transistor MOSFET . This device is the basic unit of present ultra-large-scale-integration ULSI microelectronics industry. It is estimated that MOSFET-based electronic devices now constitute close to 90 of the semiconductor device market. The MOSFET is formed by a MOS structure and two p-n junctions in which the n material is heavily doped Figure 5.1...