Physical Concepts of Quantum Dots

**11**

**Chapter 2**

**Abstract**

2D Nanomaterials

Quantum Confinement Effect of

*Ganesan Ravi, Thangavel Elangovan, Bojarajan Arjun kumar,* 

Quantum confinement is the spatial confinement of electron–hole pairs (excitons) in one or more dimensions within a material, and also electronic energy levels are discrete. It is due to the confinement of the electronic wave function to the physical dimensions of the particles. In this effect can be divided into three ways, 1D confinement (free carrier in a plane), quantum wells; 2D confinement (carriers are free to move down), quantum wire; and 3D confinement (carriers are confined in all directions), which are discussed in detail. In addition the formation mechanism of exciton and quantum confinement behavior of strong, moderate, and weak confinement have been discussed below.

*Gopal Ramalingam, Poopathy Kathirgamanathan,* 

*Nadarajah Manivannan and Kaviyarasu Kasinathan*

**Keywords:** quantum dots, energy level, exciton, confinement, Bohr radius

energy levels lead to size confinement [1–3] (**Figures 1** and **2**).

The term "quantum confinement" mainly deals with energy of confined electrons (electrons or electron hole). The energy levels of electrons will not remain continuous as in the case of bulk materials compared to the nanocrystals. Moreover, obtaining the confined electron wave functions, they become a discrete set of energy levels as shown in **Figure 1**. Such kinds of effects appear when the dimensions of the potential approach near to *de Broglie wavelength* of electrons resulting in the changes or discrete levels of energy. The effects are defined as quantum confinement and consequently, for nanocrystals, are often called quantum dots (QDs). Furthermore, this quantum dot effect has an influence in the nanomaterial properties such as electrical, optical, as well as mechanical behavior of the material. It is due to its peculiar nature why nanomaterials possess higher energy electrons than the bulk materials. Depending on the QD size, confined electrons have higher energy than the electrons in bulk materials. The semiconductor nanomaterials exhibit fascinating properties when reducing their dimensionality from 2D to 1D or 1D to 0D. Perhaps, the quantum confinement effect occurs when reducing the size and shape of nanomaterials less than 100–10 nm or even lesser. These changes due to the discrete set of electron

In order to understand to know more about quantum confinement, it is necessary to understand the phenomenon of quantum dots (QDs). QDs are the new class of materials in which quantum confinement effects can be evident. QDs are very tiny semiconductor crystals in the order of nanometer size, and also molecules are tightly confined electrons or electron–hole pairs called "excitons" (explained in

**1. Introduction of quantum confinement**
