QUANTUM WELLS, WIRES,
AND DOTS
9.1. INTRODUCTION
When the size or dimension of a material is continuously reduced from a large or
macroscopic size, such as a meter or a centimeter, to a very small size, the properties
remain the same at first, then small changes begin to occur, until finally when the
size drops below 100 nm, dramatic changes in properties can occur. If one dimension
is reduced to the nanorange while the other two dimensions remain large, then we
obtain a structure known as a quantum well. If two dimensions are so reduced and
one remains large, the resulting structure is referred to as a quantum wire. The
extreme case of this process of size reduction in which all three dimensions reach the
low nanometer range is called a quantum dot. The word quantum is associated with
these three types of nanostructures because the changes in properties arise from the
quantum-mechanical nature of physics in the domain of the ultrasmall. Figure 9.1
illustrates these processes of diminishing the size for the case of rectilinear geometry,
and Fig. 9.2 presents the corresponding reductions in curvilinear geometry. In this
chapter we are interested in all three of these ways to decrease the size. In other
words, we probe the dimensionality effects that occur when one, two, or all three
dimensions becomes small. Of particular interest is how the electronic properties are
Introduction to Nanotechnology, by Charles P. Poole Jr. and Frank J. Owens.
ISBN 0-471-07935-9. Copyright 0 2003 John Wiley & Sons, Inc.
226
AND DOTS
9.1. INTRODUCTION
When the size or dimension of a material is continuously reduced from a large or
macroscopic size, such as a meter or a centimeter, to a very small size, the properties
remain the same at first, then small changes begin to occur, until finally when the
size drops below 100 nm, dramatic changes in properties can occur. If one dimension
is reduced to the nanorange while the other two dimensions remain large, then we
obtain a structure known as a quantum well. If two dimensions are so reduced and
one remains large, the resulting structure is referred to as a quantum wire. The
extreme case of this process of size reduction in which all three dimensions reach the
low nanometer range is called a quantum dot. The word quantum is associated with
these three types of nanostructures because the changes in properties arise from the
quantum-mechanical nature of physics in the domain of the ultrasmall. Figure 9.1
illustrates these processes of diminishing the size for the case of rectilinear geometry,
and Fig. 9.2 presents the corresponding reductions in curvilinear geometry. In this
chapter we are interested in all three of these ways to decrease the size. In other
words, we probe the dimensionality effects that occur when one, two, or all three
dimensions becomes small. Of particular interest is how the electronic properties are
Introduction to Nanotechnology, by Charles P. Poole Jr. and Frank J. Owens.
ISBN 0-471-07935-9. Copyright 0 2003 John Wiley & Sons, Inc.
226