Point-contact Diodes Research Articles

Rectifying Properties of W-Ni Point Contact Diode in CO2 Laser Radiation

The current-voltage characteristics of a tungsten-nickel point contact diode at audio frequencies and the d.c. voltage across the diode when illuminated with CO2 laser radiation have been studied as a function of the applied d.c. bias. A large value of the rectified d.c. voltage was detected, when a complicated asymmetry in the I-Vb curve was observed. The characteristic with this asymmetry is not consistent with the simple tunneling theory, in which only the difference between the work functions of the metals in contact is taken into account. The Vdc-Vb characteristics calculated from the I-Vb curve by the assumption of the current controlled rectification agree well with the observed Vdc-Vb curves. This fact shows that the diode is a phase detector.

Effect of d-electrons on the frequency response of metal-insulator-metal devices

The frequency limitation of metal-insulator-metal point-contact diodes is interpreted in terms of the fundamental electronic band structure of the metal whisker. It is shown that the response at optical frequencies depends on the partial delocalization of the d-electrons resulting in a different cut-off frequency for transition and noble metals. The implications for diode design are discussed.

Comparison of Methods for Sensitivity Determination of Point-Contact Diodes at Submillimeter Wavelength

Three independent methods were used: 1) mixing of two HCN lasers; 2) mixing of the sixth harmonic of a klystron with an HCN laser; and 3) the incremental-loss method. The results are given. The most sensitive configuration was obtained using a corner reflector. The influence of local-oscillator (LO) power on the conversion losses of the diodes are investigated.

Characteristics of W–Ni Point Contact Diodes as Infrared Antennas

Characteristics of W–Ni Point Contact Diodes as Infrared Antennas

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.

The use of antenna theory to calculate the electric fields in a thermal field emission metal whisker diode

In recent years, research groups have used metal-metal point contact diodes for frequency mixing and detection of infrared laser radiation. It has been postulated that the mechanism for the nonlinear current-voltage characteristic of the diode is the tunneling of electrons through an intermediate oxide film from the whisker tip to the metal base, i.e., the configuration is considered to be a metal-oxide-metal (MOM) tunneling junction. Several features of the diodes' operation create considerable doubt concerning the applicability of the MOM tunneling mechanism. Analysis of the available data led us to postulate an alternate solid state mechanism, namely a thermally enhanced field emission process. Such emission would be a consequence of the immersion of the whisker in the laser radiation resulting in (1) conduction heating which induces thermionic emission and (2) generation of an electric field at the tip necessary for electron tunneling. In an earlier paper, we calculated the power absorbed by the cylindrical shank of a point contact diode in an infrared radiation field. Using the absorbed power as a source, detailed calculations were made of the laser induced temperature distributions on the diode; more approximate treatments were used to obtain the electric fields developed on the tip. Values of the computed temperature and field parameters for tungsten were found to be consistent with a thermal field emission process. In this paper we present a more rigorous calculation of the voltages and fields induced on different metal whisker tips by the incident laser radiation. Linear antenna theory is used to describe the receiving properties of the diode. The actual pointed geometry of the diode tip has been taken into account using Schelkunoff's theory of the conical antenna. The electric fields at the tip are found to be comparable with those necessary for field emission. The highest fields are established on gold tips, consistent with the experiments of Green et al. who found the best responsivity occurs with gold-gold contacts. Finally we discuss the significance of the experimental results of Young et al. on metal-vacuum-metal tunneling characteristics to the MOM tunneling hypothesis.

Measuring and minimizing diode detector nonlinearity

This paper describes two techniques for measuring the linearity of amplitude detectors in general, and for measuring the deviation from square-law E of point-contact diode detectors in particular. A general mathematical model is given for determining the RF input power as a function of the detector output voltage. It is shown how to choose the value and the temperature coefficient of the video load resistance to minimize E and make E independent of temperature.

High-order submillimeter mixing in point-contact and Schottky diodes

The 337-μm radiation of an HCN laser has been mixed with the radiation of a 3-mm kylstron in a harmonic mixer employing various types of diodes. Beat notes resulting from different orders of mixing, occurring at frequencies as high as 4.5 THz, could be directly observed on the scope. Gallium arsenide appeared to be the most favorable diode material, whereas the Schottky barrier type produce slightly better results than the conventional GaAs point-contact diodes. The performance of the heterodyne system at 891 GHz is given in terms of sensitivity (NEP) and conversion loss (Lc).

Thermal and field emission effects of laser radiation on metal whisker diodes: Application to infrared detection devices

In a series of recent experiments, research groups have made absolute frequency measurements with laser beams in the infrared region of the spectrum (λ ≲ 10 μm) using a metal point contact diode for generation, frequency mixing and detection. It has been postulated that the mechanism for the nonlinear current-voltage characteristic of the diode is tunnelling of electrons through an intermediate oxide film from the whisker into the metal base, i.e., the configuration is considered to be a metal-oxide-metal (MOM) tunnelling junction. Several features of the diode's operation create considerable doubt concerning the applicability of the MOM tunnelling mechanism. Analysis of the available experimental data led us to postulate an alternate solid state mechanism, namely a thermally enhanced field emission process. Such emission would be a consequence of the immersion of the whisker tip in the laser radiation resulting in (1) conduction heating which induces thermionic emission and (2) generation of an electric field at the tip necessary for electron tunnelling by field emission. In this paper we calculate rigorously the power absorbed in the metal whisker from the incident radiation. From the power absorbed, the heat conduction equation is solved for model geometries to obtain the laser induced temperature distribution at the whisker surface. Estimates of the electric field are obtained and combined with temperature calculations to obtain the nonlinear I– V characteristics of the thermally enhanced field emission model. Finally some simple experiments are proposed to test the thermal field emission hypothesis as a possible mechanism to explain the nonlinear characteristics of the metal whisker point contact diode.

Far infrared frequency synthesis with stabilized CO<inf>2</inf>lasers: Accurate measurements of the water vapor and methyl alcohol laser frequencies

A far infrared (FIR) frequency synthesis technique using saturated-absorption stabilized CO 2 lasers and a point-contact diode has been used to measure frequencies of a number of strong CW H 2 O, D 2 O, and CH 3 OH laser lines. The first frequency measurements of the 79-μm H 2 O, the 73- and 108-μm D 2 O, and 11 CO 2 -pumped CW12CH 2 16OH laser lines are reported. This measurement is the first demonstration of the general usefulness of CO 2 lasers for accurate synthesis of FIR frequencies.

Detection of 890 GHz radiation with a metal-oxide-metal diode

An investigation was made of the behavior of a W–Co point-contact diode in video and heterodyne detection of 890 GHz radiation. It was found that additional oxidation of the substrate could increase the responsivity of the diode by a factor in excess of 2.

Extension of absolute frequency measurements to 148 THz: Frequencies of the 2.0- and 3.5-μm Xe laser

Absolute infrared frequency measurement has been extended to 148 THz (the highest frequency ever directly measured) with measurement of the two strong cw laser lines of Xe. The frequencies were synthesized with stabilized CO2 and 3.39-μm He-Ne lasers and mixed on a W-Ni point-contact diode. The measured frequencies are νXe(2.0μm)=147.915 850(15) THz and νXe(3.5μm)=85.459 997(3) THz.

Anomalous I-V Characteristics in Mg-Doped GaN Point Contact Diodes

Anomalous I-V Characteristics in Mg-Doped GaN Point Contact Diodes

Conditions for Using Tungsten-Nickel Point Contact Diodes as Harmonic-Generator Mixers

Conditions for Using Tungsten-Nickel Point Contact Diodes as Harmonic-Generator Mixers

Mechanism and properties of point-contact metal-insulator-metal diode detectors at 10.6 μ

Detection mechanisms of point-contact MIM diodes at 10.6 μ wavelength have been studied. Detailed measurements of the static current-voltage characteristic and its first and second derivatives as functions of bias voltage were made simultaneously with infrared sensitivity measurements. The results indicate that the static current-voltage characteristics extend to infrared frequencies. We find that thermal effects do not contribute significantly to detection at this wavelength, and that the tungsten whisker acts as a rather efficient receiving antenna. The antenna and its shunting capacitance apply a 3×1013-Hz ac voltage to the diode which in our experiment has amplitude 124 mV, through an impedance which is much less than the junction impedance. The diode nonlinearity d2I/dV2 varies from 6.5×10−5 to 6.7×10−3 A/V2 as dc bias increases from 0 to 300 mV. None of these conclusions apply to detection at 6328 Å; it is found that detection in the visible is dominated by thermal or photoconductive effects.

Enhanced optical frequency detection with negative differential resistance in metal-barrier-metal point-contact diodes

Enhanced optically induced voltages have been observed across the junction of metal-barrier-metal point-contact diodes which exhibit a current-controlled negative differential resistance. Responsivities in excess of 5 V/W have been demonstrated when the incident optical beam is focused to ∼1 W/cm2 at the junction. This enhancement is in agreement with the behavior expected from the rectification of the optical field.

Numerical analysis of semiconductor devices with planar, cylindrical and radial symmetry†

An approach is described which has been uaod to analyse semiconductor-devices with planar, cylindrical and radial symmetry using a generaL numerical analysis programme. Using this approach, carrier distributions in planar and point-contact Schottky diodes are compared.

Characteristics of tungsten-nickel point contact diodes used as laser harmonic-generator mixers

Properties of tungsten-nickel point contact diodes, when used as harmonic-generator mixers, were measured. The measured properties are those which will be useful to workers wishing to use these high-speed devices (faster than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-14</sup> s). Some of the properties measured were : the decrease in signal with mixing order; the detected signal as a function of laser frequency; and the power required to optimize the harmonic beat notes.

Radiation of difference frequencies produced by mixing in metal-barrier-metal diodes

Millimeter radiation obtained by difference-frequency mixing of the P(20) and P(22) lines of the CO2 laser has been used to investigate the polarization, radiation pattern, and bias characteristics of metal-barrier-metal point-contact diodes. The results are consistent with antenna theory and the electron tunneling model of the point contact. Significant enhancement in performance is expected with eventual use as a submillimeter source.

New Frequency Measurements and Techniques in the 30-THz Region

It is proposed that the frequency differences between CO2 laser ines and the harmonics of these differences might be used as intermediate frequencies to bridge the gap between microwave frequency standards and infrared frequencies to simplify absolute measurements of the latter. Tungsten-nickel point-contact diodes would be used as harmonic generators and mixers. The preliminary results of an experimental feasibility study are presented. A description of a novel two-frequency laser, built for this study, is given. It is shown that beat frequencies between differences up to 715 GHz and microwave frequency harmonics up to the twelfth can be observed; interactions with at least the third harmonic of a CO2 frequency difference are possible, producing signals with an S/N of 51 dB in a 2.2-s time constant receiver; attempts to observe a beat between a CO2 frequency and the seventh harmonic of a difference were not successful.