No abstract

No abstract

We present the first direct evidence of hot electrons traversing ballistically a thin GaAs layer. The energy distribution of the hot electrons associated with the momentum in the direction of the current was measured with the use of a tunneling-hot-electron-transfer amplifier as an electron spectrometer. The width of the ballistic peak was found to be about 60 meV for hot electrons with excess energy of some 300 meV above the thermal electrons. Those values are close to the expected initial injection values. PACS numbers: 72.20.i As the dimensions of semiconductor devices get smaller, the probability that electrons can traverse them without scattering at all, i.e. , ballistically, increases. Under these conditions the transport of electrons in the solid resembles that in vacuum, but with the effective mass and group velocity of the electrons in the semiconductor.A purely ballistic transport model was first calculated by Shur and Eastman. ' In a diode structure composed of n+-n -n+ layers, with the ballistic transport occurring in the n layer, a dc current-voltage characteristic at high injection levels was shown to obey the Child-Langmuir law I -V of a vacuum-tube diode if ideal boundary conditions were assumed. However, more realistic boundary conditions (due to carrier spillover from the n+ layers into the n layer) led to a different I Vcharacteristi-c, 2 which made the ballistic effect difficult to prove. Note also that most test structures suffered from inherent difficulties. Typical examples were large series resistances due to the Ohmic contacts and transport regions which could not be made short enough for the observation of the effect. 3 Three-terminal structures have been used as electron spectrometers and have demonstrated that hot electrons traverse thin semiconductor layers,~7 but no evidence for ballistic transport has been reported. We have measured the energy distribution of hot electrons at low temperatures, after they have traversed a thin n+-GaAs layer and were collected by a heterojunction collector. As we will show, about 50% of the injected hot electrons reached the collector without any measurable loss of energy, which proves for the first time the existence of ballistic transport in semiconductors.The energy diagram of the device used for this experiment is shown schematically in Fig.

Electrostatic focusing of ballistic electrons in a high-mobility two-dimensional electron gas is discussed and experimentally demonstrated. The focusing is achieved by a spatial modulation of the electrostatic potential along the electrons trajectories, in analogy with the modulation of the dielectric constant in conventional light-wave optics.The long electronic mean free path (mfp) in twodimensional electron-gas (2D EG) systems and improved electron-beam lithography have opened a new field of research which might be called "electron optics in solids. "A few recent examples are magnetic focusing, ' the collimation of an electron beam injected from a smooth con-

A narrow channel patterned in a novel GaAs heterostructure with tunable electron density is used to study the conductance of the electron gas in the very low-density regime where only a single one-dimensional subband is occupied. Periodic oscillations of the conductance versus density and nonlinearities in the conductance suggest the formation of a one-dimensional charge-density wave or Wigner crystal.A one-dimensional electronic system (1DES) is expected to have exotic quantum states, ' and has been the focus