We will come across many people in our life. They will all have a purpose (good/ bad) to fulfill. Some will teach us a lesson and some will leave our soul wounded. Some will love us for their selfish motives and some will love us “unconditionally” (the real good ones). Some will cheat us, lie to us and stab us in our back or absence. Learn from the lessons that life teaches us and don’t waste our time on people who are there in our life for their convenience and who never take us seriously. Don’t allow people to use us for their happiness. Just be Strong and don’t let anything break us or leave us shattered. We should choose the people whom we want in our life…………..whatever be the circumstances, we should never give up if our heart and soul knows what we are doing? for the right cause or action i.e. unconditionally.
Since the invention of the transistor by John Bardeen and William Shockley in 1948 constant miniaturization has led to devices with dimensions well below the 100 nm limit. Devices which exhibit charging effects including Coulomb blockade are known as single-electron devices. The name “single electron transistor” comes from the observation that the transistor turns on and off again every time a single electron is added to it. In this case, single electron transistor consists of a semiconductor and AlGaAs separated from metal electrodes by an insulator. The AlGaAs is doped with Si, which donates electrons. The resulting positive charge on the Si atoms creates a potential that holds the electrons at the GaAs or AlGaAs interface, creating a two dimensional electron gas. When the artificial atom has a spin, the tunneling results in the form of a chemical bond between the artificial atom. This is the origin of the Kondo effect, generally associated with magnetic impurities in metals. The mesoscopic phenomena coulomb blockade and the Kondo effect are common in SET.
Molecular beam epitaxy is used to grow the GaAs/AlGaAs structure. Electron beam lithography is used to fabricate the electrodes. With the increase in voltage on the gate electrode, keeping potential minimum, in which the electrons are trapped, becomes deeper causing the number of trapped electrons to increase.
The conductance changes by several orders of magnitude almost periodically in terms of gate voltage Vg causing the number of trapped electrons to increase. The charge in the trap increases in discrete steps, and this is reflected in the conductance between source and drain unlike a conventional transistor, in which the charge increases continuously.
The research on SETs looks very bright and semiconductor material can be replaced by graphene in the near future. There are strong efforts around the world to observe charge quantization by making the artificial atoms in SETs smaller. These involve self-assembly techniques and novel nano-lithography and oxidation methods whereby artificial atoms can be made nearly as small. This will be helpful in using SETs for practical applications. However, as SETs get smaller, all of their energy scales can be larger, so it is very likely that new phenomena will emerge at the mesoscopic level.
1. M. A. Kastner, Single electron transistor and artificial atoms, Ann. Phys. (Leipzig) 9 (2000) 11–12, 885 – 894.
2. M.A. Kastner, Physics Today 46 (1993) 24.