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

量子阱中的载流子动力学及其相关的异质结构（HS）是决定各种量子HS器件性能的关键因素；在这个项目中，我们研究了W激光器，谐振隧道二极管（RTD）和hsfet的动力学。(1) W中的复合动力学：尽管激子和自由载流子在W中的相对作用存在争议，但由于激子在高激发条件下被猝灭，W激光器中的辐射复合很可能是由自由载流子过程主导的。利用皮秒激光脉冲确定了这种自由载流子的寿命，并用带间跃迁理论很好地解释了这种寿命。(2) rtd中的隧穿动力学：由于电子在双势垒rtd中隧穿涉及到多重反射，可能会导致固有的时间延迟。我们第一次成功地测量了这种延迟，并证明了这种延迟可以用理论很好地解释。(3)高速场效应管中的加速动力学：建立了HEMT和其他高速场效应管的电子速度场关系，揭示了速度饱和的关键机理。将这一发现应用到HEMT器件建模中，表明了低场迁移率对于实现高gm和高漏极电流的重要性。

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.