Novel tunneling barrier designs for resonant tunneling diodes

Resonant Tunneling Devices are based on quantum transport of electrons through ultra-thin heterostructure layers. These devices have the potential to become the foundation for the next generation of ultra-high speed electronics and multi-values logic devices. Resonant Tunneling Diodes (RTD) provide an excellent research vehicle to study the fundamentals of electron transport in ultra-thin layered semiconductors.; Effects of X-valley transport of electrons were studied in triple barrier RTDs with significantly different AlAs barrier thickness. We have found that the electron tunneling through GaAs/AlAs quantum well structures is dominated by {dollar}Gamma{dollar} valley tunneling when AlAs layer is thin (less than 30A) and bias is low. Electron tunneling through X valley dominates when AlAs barrier is thick (more than 130A). The X valley tunneling is significant when bias is sufficiently high so that the Fermi level in front of the tunnel barrier is equal to or higher than the X barrier height in AlAs barrier.; The effects of Si impurity scattering on double barrier resonant tunneling diode (DBRTD) performance were studied by systematically varying the Si doping levels in the AlAs barriers and measuring the current-voltage characteristics of the DBRTDs. The results show that the resonant tunneling diode performance is virtually unaffected by up to 1.2 {dollar}times{dollar} 10{dollar}sp{lcub}17{rcub}{dollar}cm{dollar}sp{lcub}-3{rcub}{dollar} Si doping in the AlAs barrier. Reasonably good peak-to-valley current ratio (PVCR) is observed even with 3 {dollar}times{dollar} 10{dollar}sp{lcub}18{rcub}{dollar}cm{dollar}sp{lcub}-3{rcub}{dollar} Si doped AlAs barrier. Improvement in PVCR of DBRTDs by using two step spacer layers has been attributed to the band bending in the spacer layers.; An improved design of DBRTD with an AlGaAs chair barrier has been introduced. The chair barrier is a low AlGaAs barrier in front of an high AlAs barrier. DBRTD with different chair barrier structures were fabricated and characterized. The highest room temperature PVCR for AlGaAs/GaAs DBRTD to date, 6.0, was observed in the chair barrier structure with an Al{dollar}sb{lcub}0.25{rcub}{dollar}Ga{dollar}sb{lcub}0.75{rcub}{dollar}As chair barrier in the cathode side. The improvement in PVCR is attributed to the reduction of two valley current components by the AlGaAs chair barrier. These components are tunneling current from the accumulation layer and tunneling through the X valley in the barrier. The chair barrier structures provide an extra design parameter for optimizing DBRTDs for specific applications.