Resonant tunneling and intraband transitions in quantum wells and their device applications

Theoretical studies of resonant tunneling in semiconductor quantum well structures have been carried out for both time-independent and time-dependent cases. Calculations of a new tunneling contribution (two-body term) have been made within Tsu-Esaki's original model. A generalized unitarity relation is derived for the present scattering problem. A compact tunneling current expression is found, which includes many-body Fermion effects. Frequency limit of double barrier oscillators has been studied considering both quantum mechanical tunneling processes and circuit constraints. It is shown that the standard theoretical approach to resonant tunneling together with a unitarity bound leads to a lower bound on the negative differential resistance which is in turn related to the maximum oscillator frequency. Double barrier diodes are also considered for logic applications. The theoretical lower bound on switching times is found to be in the picosecond or subpicosecond range with appropriately designed GaAs-AlGaAs devices.; Intraband transition processes can be used for both infrared detection and source applications. A fast quantum well photodetector concept is developed, in which a specific intraband process (intersubband transition) is employed together with resonant tunneling to achieve high speed operations. Device parameters are discussed for application as a high data rate receiver for use with long wavelength non-silica fibers. Aimed at infrared and/or microwave source applications, radiative transitions associated with intraband electron tunneling through dc biased quantum well structures are analyzed. The absence of an inherent long wavelength emission cutoff is in contrast with interband transition devices. The radiative transition rate is compared with the damping loss.; Finally, some theoretical issues pertaining to the detailed device modeling have also been investigated. (a) Lattice mismatch and band offsets is strained quantum wells are studied. It is found that a potential barrier, normally associated with a band offset, acquires an additional energy-dependent term. (b) Light-heavy hole mixing is analyzed, and an effective potential is constructed which describes mixing within the effective mass theory. (c) Image force effects due to different permittivities in different planar regions are discussed. The effects are generally small enough to justify dropping them and employing the widely-used square well potential.