Real-space Electron Transfer Research Articles

High-field transport in organometallic VPE AlxGa1-xAs transferred-electron devices

The velocity-field characteristics of hot electrons in planar organometallic vapor phase epitaxial (VPE) Al x Ga 1-x As (0.1 ≤ x ≤ 0.6) transferred-electron devices have been measured by the probe technique. The characteristics in layers with x ≤ 0.30 show normal subthreshold behavior. For x > 0.30, the characteristics exhibit high values of drift velocity. The effects are more enhanced when an undoped 0.4-µm GaAs buffer layer is grown first on the GaAs: Cr substrate before the ternary layer is grown. Monotonically increasing drift velocities with electric field, with a value of 2 × 107cm/s at 6 kV/cm, have been measured in these devices. These effects and overshoots in the pulsed current-time profiles indicate the onset of real-space electron transfer at the heterointerface at high fields.

Monte Carlo simulation of real-space electron transfer in GaAs-AlGaAs heterostructures

The Monte Carlo method has been used to simulate electron transport in GaAs/AlGaAs heterostructures with an electric field applied parallel to the heterojunction interface. The simulations indicate that a unique physical mechanism for negative differential conductivity is provided by such layered heterostructures, which is analogous in many respects to the Gunn effect. This mechanism has been termed ’’real-space electron transfer’’ since it involves the transfer of electrons from a high-mobility GaAs region to an adjacent low-mobility AlGaAs region as the applied electric field intensity is increased. The simulations further indicate that the important details of the resulting velocity-field characteristics for these layered heterostructures can be controlled primarily through material doping densities, layer thicknesses, and the material properties of the individual layers. Thus, the phenomenon of real-space electron transfer potentially provides the ability to ’’engineer’’ those basic material properties which influence the performance of negative resistance devices.

Real-space electron transfer by thermionic emission in GaAsAl xGa 1−xAs heterostructures: Analytical model for large layer widths

Calculations are presented for negative differential resistance (NDR) and switching in layered GaAsAl x Ga 1− x As heterostructures with a high electric field parallel to the interface. The mechanism is based on thermionic emission of hot electrons from the GaAs layers into the Al x Ga 1− x As layers. An analytical model is obtained in the limit of relatively large layer widths (400 Å or wider). The method of moments is employed to solve the Boltzmann equation, assuming a position-dependent electron temperature and Quasi-Fermi level in the Al x Ga 1− x As layers, and a position-independent electron temperature and Quasi-Fermi level in the narrower GaAs layer. Thermal conduction of hot electrons from the GaAs layer into the Al x Ga 1− x As layers is taken into account. The results of the calculations show that the threshold electric field for the onset of NDR and the peak-to-valley ratio can be controlled to a large extent by adjusting the mobility of the Al x Ga 1− x As layer, the layer dimensions, and the potential barrier (Al mole fraction in the Al x Ga 1− x As).

Negative differential resistance through real-space electron transfer

A new mechanism is proposed to obtain negative differential resistance in layered heterostructures for conduction parallel to the interface. The mechanism is based on hot-electron thermionic emission from high-mobility GaAs into low-mobility AlxGa1−xAs. Preliminary calculations indicate that high peak-to-valley ratios can be achieved. The transfer speed is estimated to be of the order of 10−11 s. We further show that the concept of hot-electron thermionic emission can be applicable to a variety of devices.