Quantum confinement effect
Due to quantum confinement the electronic and optical properties of a material changes as its size goes to around 10nm or less and using this property two dimensional semiconductors which are confined to operating in a two dimensional space can be created. Because of their unique properties, they can be put to use in highly specialized quantum optical and electrical applications. So far research on these semiconductors has been done using materials like graphene.
Quantum membranes
Nanoscale size effects drastically alter the fundamental properties of semiconductors. A team of researchers at the University of California, Berkeley, has developed a two-dimensional semiconductor called quantum membranes (QM) using indium arsenide having a band structure and can be turned from a bulk material to a two-dimensional one by reducing its size. The unique feature of QMs is that they can be used as a free standing material and thus can be used with a variety of substrates, unlike other such structures which are based on just a single one.
Quantum membrane fabrication
To make the QMs, indium arsenide is grown in a GaSb and AlGaSb substrate. Then the top layer is made into the required shape and the bottom layer is etched away. The remaining indium arsenide layer is then moved to whichever substrate is desired to make the final product.
Properties
In addition to adding a new material to the bank available to researchers in using semiconductor materials, the results of this work also provide insight into how structurally confined materials work which could lead to more materials with truly unique properties. The electrical properties of the material indicate that electron mobility does not depend on the field that was applied, except in the case of very high fields, which is quite different from conventional semiconductors.
Investigations have been carried out on the dominant role of quantum confinement in the field-effect device properties of free-standing InAs nano membranes with thicknesses varying from 5–50 nm.
Optical absorption studies were also performed by transferring InAs “quantum membranes” (QMs) onto transparent substrates, from which the quantized sub-bands are directly visualized.
It was observed by the researchers that these sub-bands determine the contact resistance of the system with the experimental values consistent with the expected number of quantum transport modes available for a given thickness. Also, the effective electron mobility of InAs QMs is shown to exhibit anomalous field and thickness dependences that are in distinct contrast to the conventional MOSFET models, arising from the strong quantum confinement of carriers. The researchers claim that results provide an important advance toward establishing the fundamental device physics of two-dimensional semiconductors.