Research on Dynamics of Two-dimensional Carriers in Ultrathin semiconductor Heterostructure Devices

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Dynaics of carriers in quantum wells ( Ws) and related hetero- structures (HS) are the key factor that dominates the performances of various quatntum HS devices; in this project, we investigate dynamics in W lasers, resonant tunneling diodes (RTD), and HSFETs.(1) Recombination dynamics in Ws: Although a controversy exists as to the relative roles of excitons and free carriers in Ws, the radiative recombination in W lasers may well be dominated by the free carrier process, since excitons are quenched under a high excitation condition. The lifetime of such free carriers is determined by using picosecond laser pulse and found to be well explained by the theory of band-to-band transition.(2) Tunneling dynamics in RTDs: Since electrons tunneling through double-barrier RTDs involves the multiple reflection, it may lead to an intrinsic time delay. We have successfully measured this delay for the first time and nave shown that this delay is well explained by the theory.(3) Acceleration dynamics in HSFETs: The velocity-field relationship of electrons is established for HEMT and other HSFETs and key mechamisms for velocity saturation are disclosed. Implementation of thie finding to HEMT device modeling has shown the importance of low field mobility for the achievement of high gm and high drain current.