This paper presents theoretical calculations of the large-signal admittance and efficiency achievable in a silicon p-n-v-ns Read IMPATT diode. A simplified theory is employed to obtain a starting design. This design is then modified to achieve higher efficiency operation as specific device limitations are reached in large-signal (computer) operation. Self-consistent numerical solutions are obtained for equations describing carrier transport, carrier generation, and space-charge balance. The solutions describe the evolution in time of the diode and its associated resonant circuit. Detailed solutions are presented of the hole and electron concentrations, electric field, and terminal current and voltage at various points in time during a cycle of oscillation. Large-signal values of the diode's negative conductance, susceptance, average voltage, and power-generating efficiency are presented as a function of oscillation amplitude for a fixed average current density. For the structure studied, the largest microwave power-generating efficiency (18 percent at 9.6 GHz) has been obtained at a current density of 200 A/cm2, but efficiencies near 10 percent were obtained over a range of current density from 100 to 1000 A/cm2.

Large-signal analysis of a silicon Read diode oscillator

A general expression is derived from which the spectral density of the noise generated in a uniformly multiplying p-n junction can be calculated for any distribution of injected carriers. The analysis is limited to the white noise part of the noise spectrum only, and to diodes having large potential drops across the multiplying region of the depletion layer. It is shown for the special case in which \beta = k\alpha , where k is a constant and α and β are the ionization coefficients of electrons and holes, respectively, that the noise spectral density is given by 2eI_{in}M^{3}[1 + (\frac{1 - k}{k})(\frac{M - 1}{M})^{2}] where M is the current multiplication factor and I in the injected current, if the only carriers injected into the depletion layer are holes, and by 2eI_{in}M^{3}[1 - (1 - k)(\frac{M - 1}{M})^{2}] if the only injected carriers are electrons. An expression is also derived for the noise power which will be delivered to an external load for the limit M \rightarrow \infin .

Multiplication noise in uniform avalanche diodes

Molecular beam epitaxy

One of the "fundamental" problems in the continued scaling of MOSFETs is the 60 mV/decade room temperature limit in subthreshold slope. In this paper, we report initial studies on a new kind of transistor, the I-MOS. The I-MOS uses modulation of the breakdown voltage of a gated p-i-n structure in order to switch from the OFF to the ON state and vice versa. Since impact-ionization is an abrupt function of the electric field (or the carrier energy), simulations show that the device has a subthreshold slope much lower than kT/q. Simulations also show that it is indeed possible to make complementary circuits with switching speeds comparable to or exceeding CMOS. Experimental results on a silicon based prototype verify the basic concept and show very steep subthreshold slopes with high speed turn-on and turn-off. Lower bandgap materials are also being investigated to reduce the value of the breakdown voltage and permit lower voltage operation.

I-MOS: a novel semiconductor device with a subthreshold slope lower than kT/q

The short‐circuit photocurrent from an avalanche photodiode is calculated using an exact solution of the differential transport equations for the multiplication region. The dcelectric field and the hole and electron velocities are assumed constant in the avalanche region into which photoelectrons are injected. It is shown that the electron‐ and hole‐ionization coefficients α and β remain constant over a practical range of multiplied photocurrents. Computer studies of the solution show that avalanche multiplication does not reduce the device bandwidth as long as the dc multiplication M 0 is less than the ratio of α and β, i.e., as long as M0 α/β. The previously unspecified ``effective'' transit time, τ1, in this equation is approximately τ1 = N(β/α)τ, where N is a number varying slowly from ⅓ to 2 as β/α varies from 1 to 10−3, and τ is the multiplication‐region transit time. The complete solution of this problem thus shows that the widely different results previously obtained for β/α = 0 and β/α = 1 are continuously joined, and provides a simple criterion for judging the ranges of validity of the two limiting cases. The results emphasize the practical importance of obtaining the required multiplication at fields such that M 0<α/β where the multiplication does not affect the bandwidth. This also leads to minimum excess avalanche‐region noise, and hence to the closest possible solid‐state analog to the vacuum‐tube photomultiplier.

Avalanche‐Photodiode Frequency Response

This paper describes and analyzes a proposed semiconductor diode designed to operate as an oscillator when mounted in a suitable microwave cavity. The frequency would be in the range extending from 1 to 50 kmc. The negative Q may be as low as 10 and the efficiency as high as 30 per cent. The diode is biased in reverse so as to establish a depletion, or space-charge, layer of fixed width in a relatively high resistance region, bounded by very low resistance end regions. The electric field has a maximum at one edge of the space-charge region, where hole-electron pairs are generated by internal secondary emission, or avalanche. The holes (or electrons) travel across the space-charge layer with constant velocity, thus producing a current through the diode. Because of the build-up time of the avalanche, and the transit time of the holes across the depletion layer, the alternating current is delayed by approximately one-half cycle relative to the ac voltage. Thus, power is delivered to the ac signal. When the diode is mounted in an inductive microwave cavity tuned to the capacity of the diode, an oscillation will build up. It appears possible to obtain over 20 watts of ac power in continuous operation at 5 kmc.

W. T. Read

Papers

A proposed high-frequency, negative-resistance diode