Asuo Aishima

An analysis of wide-band transferred electron devices

The trapping conditions of a high-field domain at the anode are studied by varying doping density, applied bias voltage, and doping notch depth and width near the cathode. It is shown that the frequency band of negative conductance of the trapped-domain mode depends significantly on the doping density, and a diode having the doping density of 3 × 1015/cm3exhibits the negative conductance over the wide range from 4 GHz to 42 GHz. The upper frequency limit of the negative conductance is due to the series resistance in the low-field region and the lower limit is determined by carrier transit-time effects in high-field region. The operation mode of a trapped-domain diode will change into a traveling dipole or accumulation mode from a trapped-domain mode depending on the doping density and the operation frequency for a large-signal operation.

Negative resistance in a finite superlattice owing to quantum mechanical reflection

Sasaki [Jpn. Inst. Electron. Commun. Eng. Tech. Rep. ED‐84, 27 (1984)] has proposed a new type of superlattice, a modulation mass superlattice where the effective mass of electrons is changed periodically and the conduction‐band edge is aligned so as to eliminate potential discontinuity. We investigate the quantum mechanical transmission of electrons for the case where a voltage is applied perpendicularly to the layers. We find that the modulation mass superlattice exhibits a new type of negative resistance owing to quantum mechanical reflection of electrons. The threshold voltage of negative resistance is much lower (around 10 mV than that (above 0.1 V) of compositional superlattice. The current density of the modulation mass superlattice is two orders of magnitude greater than that of a compositional superlattice. Such properties are very desirable for achieving a low‐power ultrafast logic device.

Rectification Properties of Asymmetrical Superlattices

A rectifying superlattice which can be used for detecting THz waves is proposed. The device is created by using an effective-mass superlattice in which the superlattice cycle is gradually changed. The operating principle is based on the fact that the quantum mechanical transmission coefficient with asymmetrical geometry is asymmetrical with respect to the applied voltage. The forward current is several orders in magnitude greater than the reverse current at a relatively low applied voltage. This feature is potentially useful for detecting and mixing small signals at THz frequencies.

Numerical study of an n‐gallium arsenide diode distributed oscillator

The dynamic electron velocity, electron temperature, etc., in an n‐gallium arsenide ballistic diode have been calculated by solving the Boltzmann equation under a hydrodynamic approximation. It has been found from the results that an n‐gallium arsenide ballistic diode exhibits a negative conductance at a fairly high frequency range and over a wide frequency range from 1500.0 to 2300.0 GHz. From the small signal analysis using a simplified diode model, it has been shown that the negative conductance arises as a result of density modulation effects of the carriers, namely, space‐charge transit time effects. High growth rate, up to 300.0 Np/cm, has been predicted in an n‐gallium arsenide ballistic diode distributed oscillator. The diode can be expected to act as a new solid‐state source at a far infrared frequency range.

New Negative Conductance in GaAs n+-n-n+ Ballistic Diode –Time-Dependent Computer Simulation–

Time-dependent computer simulations were performed to investigate the high-frequency effects of a GaAs n+-n-n+ ballistic diode. A new negative conductance, found previously using a simplified diode model, was confirmed by the numerical simulation, though the results differed considerably from those obtained previously. It is demonstrated that a GaAs n+-n-n+ ballistic diode exhibits negative conductance over a wide frequency range over 1000 GHz. The diode can be expected to act as a new solid-state source in the far-infared frequency range.

New Negative Conductances in GaAs n+-n-n+ Ballistic Diodes

Two terminal conductances for GaAs n+-n-n+ ballistic diodes are calculated by using a simplified diode model. It is found from the results that, due to space charge transit time effects, negative conductances appear in such ballistic diodes at a far infrared frequency range. It is also demonstrated that diode conductance-frequency characteristics are affected significantly by the plasma oscillation frequency.

Experimental observation of large-signal behavior in trapped domain transferred electron devices

The large-signal behavior of the anode trapped domain diodes (n-GaAs) is experimentally studied. It was confirmed that the negative conductance of the diodes was bell shaped as a function of the magnitude of the terminal RF voltage, as predicted by the authors. The injection operation characteristics of the diodes were clarified: An oscillation can be initiated by applying an external microwave signal where a frequency difference between the oscillation and the signal is less than 20 MHz. While if the frequency difference becomes greater than 20 MHz, quenching behavior of oscillation is appeared due to the bell-shaped negative conductance of trapped domain diodes.

Various Space Charge Modes in TED's with Schottky Barrier Cathode Contact

Computer simulation has shown that, depending on the current injection characteristics at the cathode, five different space charge modes appear in transferred electron devices with the Schottky barrier cathode contact when time-independent diode terminal voltage is applied. In a coaxial resonant cavity, the devices operate in five different resonant space charge modes. It has also been demonstrated that, under suitable conditions, such devices exhibit the bistable switching phenomena of high speed, and high current drop ratio.

Monte Carlo Calculations of Diffusion Constant in n-InP

Ensemble Monte Carlo simulations are carried out to ascertain the magnitudes of the parallel and perpendicular diffusion constants in n-InP and their dependence on the electric field. The two-dimensional locations of 1000 electrons in real space after many accelerations by the electric field and collisions with phonons are illustrated in order to clarify the anisotropy in electron diffusion behavior. It is also demonstrated how both the parallel and perpendicular diffusion constants are affected by impurity scatterings. It is found that, because of the randomizing nature of impurity scatterings, both the parallel and perpendicular diffusion constants in n-InP with higher impurity density are greater than those in n-InP with lower impurity density.