Analysis and Simulation of Variable Range Hopping Parameters Under Photo-excitation رسالة ماجستير

Abstract

For the purpose of improving the performance of random access memory (RAM) in computers, the electrical current conduction mechanism which is governed by the variable range hopping (VRH) of electrons from one energy state to another distant site of states is reconsidered. Some recent developments that include less energy consumption, shorter time of response and less heating during run process are attained by getting use from the cheap light energy. Photoexcitation of these devices and device related materials have shown that while the variable range hopping parameters like the degree of disorder, average hopping energy, average hopping energy sharply decreases with increasing light intensity, the density of localized energy states (DOS) near Fermi level and average hopping range significantly increases. The increase of DOS with increasing light intensity is very abnormal and makes the use of Mott's variable range hopping theory questionable. The Mott's theory which was derived assuming invariant DOS was simulated to state the reasons for abnormality. In addition the validity of this theory under variable DOS was analytically proved assuming linear variation of DOS with light energy and was also tested against exponential DOS variation. Mathematical analysis of the theory and its testing parameters have shown that the Mott's model for variable range hopping is still applicable even if the DOS is variable function of energy. This study, which is carried for the first time, is supposed to provide an excellent method for increasing the ability of storage in RAM by increasing the density of states that occupy electrons and shorten the response time of the device by increasing the hopping distance and decreasing the hopping energy through the