Zero-bias Condition Research Articles

Electron interactions in the two-dimensional electron-gas base of a vertical hot-electron transistor.

We present results on the interaction of hot and cold electrons in a large-area two-dimensional electron-gas-base hot-electron transistor. Four-terminal magnetoresistance measurements of the cold electrons in the two-dimensional electron-gas (2DEG) base, as a function of forward-emitter bias, ${\mathit{V}}_{\mathrm{EB}}$, show significant deviations from the zero-bias condition. We identify two distinct regimes: (i) an enhanced interface scattering as the 2DEG is forced against the collector-barrier heterojunction for low biases before emitter-current injection and (ii) an electron-heating effect in the 2DEG once current injection occurs. We invoke a simple heat-exchange argument to analyze the relaxation of the injected hot carriers.

Slow-wave microcoplanar variable phase shifter

The phase-shifting properties of a slow-wave microcoplanar structure are studied by means of a rigorous theoretical approach and the propagation losses are calculated. The Green function, which is used for the two-dimensional determination of the depletion layer profile, satisfies the real boundary conditions of the physical structure. The results obtained for the structure's electrical length are compared with the corresponding experimental data and a good agreement is obtained, in particular for zero-bias conditions.

Roles of shallow and deep electron traps causing backgating in GaAs metal-semiconductor field-effect transistors

In GaAs metal-semiconductor field-effect transistors under backgating conditions, electrons can be trapped in ‘‘shallow’’ and deep trap levels. It is shown that the characteristics of these traps can be determined and those responsible for backgating can be identified by examining the thermally excited emission currents under zero-bias short-circuit conditions. It is established, for the first time, that there are ‘‘shallow’’ traps located under the field-effect transistor active channel, and possibly related to the ion-implantation damage, that are directly related to the backgating, although the process is initiated due to filling of deep levels by electrons near the surface of the semi-insulating GaAs.

Characterization of deep levels using unconventional zero-bias thermally stimulated current in ion-implanted semi-insulating GaAs substrates

It has been observed that by forward biasing ion-implanted n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> /SI GaAs substrate junctions, electrons can be injected and trapped at deep levels in the substrate at low temperatures, and that when thermally stimulated they give rise to a pure emission current under a zero-bias condition. Characteristics of these emission peaks Provide information concerning trap energy levels and emission sections. Results obtained using test structures on undoped and lightly Cr-doped LEC-grown materials are reported.

Silicon X-ray sensor with modified electrode structures

New surface barrier silicon sensors, which work under zero-bias conditions have been developed to investigate the applications to X-radiation, especially to energy monitoring and position sensing. Four kinds of prototype sensors have been fabricated using high purity n-type silicon to meet these requirements by changing the configuration of electrode structures. They are designed for purely X-ray energy monitoring. X-ray beam position detecting for both linear and X- Y area categories, as well as combined energy monitoring and linear position sensing function, respectively. The zero-bias condition has enabled all these sensors, with modified electrode to directly couple to the I V converter and stable operational results were obtained.

Gamma-Ray Effects on an N-Channel MOS Microprocessor (Z8002) in the Zero-Bias Condition

A Cobalt-60 gamma-ray test of Z8002 n-channel MOS microprocessors in a zero-bias condition is described and discussed. The devices were irradiated at room temperature before being functionally tested at high, room and low temperatures. For all devices the total dose failure levels were found to reduce with increasing temperature. The results of these tests have shown a wide spread in failure level with temperature for one of the two manufacturer's products examined (AMD) with high temperature failure first recorded as low as 13.1 Krads (Si), after testing devices from three batches. The other manufacturer's product to be examined (Zilog) had a considerably better worst case failure level of 35.1 Krads (Si) at high temperature, but this result is based on devices taken from a single batch. Some limited parametric testing has provided trend information on supply current, input leakage and threshold voltage change versus total dose. Room temperature annealing effects on post irradiation performance were also studied for an approximate 40 day period and significant changes were found to occur.

Detection of 10-μ radiation with point-contact Schottky diodes

Point-contact Schottky diodes have been used to detect 10.6-μ radiation. Best results were obtained with n-Ge/W contacts. These gave voltage responsivity about an order of magnitude larger than typical metal-oxide-metal point contacts under zero-bias conditions, although with higher source impedance.

Spike-notch structure of (AlGa)As heterojunctions

The I-V characteristics and optical properties of (AlGa)- As p-n heterojunctions, with a larger bandgap on the n side, were studied. The discontinuity of conduction bands, tilted by the space-charge electric field, produces a spike-notch structure. At comparable low doping levels on both sides of the heterojunction, the notch is empty at zero-bias conditions and acts as a trap for injected electrons. Thermal injection into the p-type region becomes the predominant current mechanism after the notch has been filled with electrons. The notch population is a step function of the applied voltage and determines an S-shaped I-V characteristic. Radiative recombination and ac photocurrent under dc bias gives further support for the existance of captured electrons in the notch.

The Spacistor

A brief description is given of several Spacistor structures and the techniques of fabrication. Detailed measurements of the four-pole parameters are reported and described with the aid of physical models. The mutual conductance is shown to depend upon injector-modulator spacing, injector current and modulator bias, with little variation to 25 Mc. Improvement in both g <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> and shielding is shown to occur when the modulator is injecting charge. Values of g <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> of the order of several hundred micromhos have been observed. The input resistance depends upon the characteristics of the modulator contact in the space-charge region and upon the dc bias. Under forward-biased modulator conditions (optimum g <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> ) values of input resistance of the order of several hundred thousand ohms are obtained. Under zero-bias or reverse-bias conditions (somewhat reduced g <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> ), values of several megohms are obtained. Values of output resistance ranging to several hundred thousand ohms have been observed with possibilities of larger values being obtained with improved design. Low frequency voltage gain of the order of 10 and power gain of the order of several hundred have been exhibited. The reduction of power gain at 25 Mc is attributed mostly to the array of contact and device resistances, and device and header capacities, some of which may be reduced by appropriate design. These prevented the elimination of shunting capacities and precluded higher frequency measurements.