The Oratical Investigation On Dwell Time In Double Barrier Quantum Well

Since the early 1930s, there have been many attempts, especially in recent years, to answer the question"what is the average length of time spent in a classically inaccessible region by an incident tunneling particle?"The double-barrier heterostructure (DBH) research work was pioneered by Tsu, Esaki, and Chang, since then quantum transport of electrons in double barrier resonant-tunneling (DBRT) heterostructure has been extensively investigated and studied. The negative differential resistance (NDR) observed in these heterostructures has already been applied in the development of fast devices such as micro-millimeter-wave oscillators and ultra fast logic elements. These works motivate a detailed research of the dynamics of these tunneling events, especially estimation of the various time scales for tunneling events. However, electron transport process in these heterostructures system is far from being completely understood, there is still considerable controversy and confusion in the literature about the basic concept and definition of tunneling time.For the transport process of electron resonant tunneling through a double barrier heterostructure system there exist various dynamic characteristic such as the time to tunnel through a barrier (traversal time), the time required for the wave packet to travel through the entire structure (transit time), the build-up time or charging time, and the escape time of electrons from the quantum well, as well as the dwell time of electrons residing in the quantum well. More research work is needed to clarify these concepts. Although there are different notions of tunneling events in the DHB, it is generally accepted that calculation of quantum transport of electrons using dwell time will achieve a better result.The dwell time for an electron tunneling though a single rectangular barrier is calculated by the continuous condition of the wave function, We find that dwell time increases with enegy of the incident particle. Then we study the one-dimensional symmetric AlAs-GaAs-AlAs DBQW and consider barrier heights V of 0.29988 eV,the width of the barrier and the well are 4 nm and 10 nm, respectly. Particle transmission through one quantum well, which is enclosed by two tunneling barriers, can exhibit sharp peaks when the incident-particle energies coincide with the energies of the quasi-bound states of the quantum well.We study the dwell time in each barrier and quantum well, and find its'contribution to the total dwell time. To have a quantitative feeling about the effects of the barriers and the quantum well on the incident particle, it is necessary to perform numerical calculations on the times (n) that the particle travels inside the structure. The influence of well width, barrier width on dwell time characteristic curves are also discussed. We find that dwell time increases with the width of quantum well or quantum barrier.In conclusion, transmission and reflection probabilities only reflect the character that the particle appear on the right side or the left side after a long time, there are already applicable method, the focus of our study is to find out the mean time spent by a particle in quantum barrier or well, and this is very important for designing quantum device.