Pure Shot Noise Research Articles

Low frequency noise in Schottky barrier contacts of titanium nitride on n-type silicon

The electrical characteristics and the low frequency noise of Schottky contacts on n-type Si(100) have been systematically measured. The thin films were deposited by reactive magnetron sputtering at room temperature. Based on a model of a parallel combination of an ideal diode of current and a generation-recombination diode of current , we have extracted the contribution of both diodes to the measured total current I. Treating the two components and as different noise generators, we have analysed the observed white noise at high frequencies and the excess current noise at lower frequencies. The white noise is explained by using a pure shot noise for the component , by applying Gupta's general theorem on noise in non-linear driven devices for the component and by considering an additional noise generator with a Nyquist-type intensity. The excess current noise is explained by a model based on fluctuations of the generation-recombination current only. Analysis of the versus I data allowed us to determine the interface state density.

Method for determining the electron number in charge-coupled measurement devices

The conversion factor in a CCD device is determined by the photon transfer technique in a region where pure shot noise is not dominating, i.e., where noise of the readout electronics must be taken into account. The method is based on the measurement of the noise standard deviation, dependent on the intensity of the signal and the fifing of a simple model incorporating shot noise and signal-independent noise. The result is a linear equation system. From its solution the conversion factor and the standard deviation of the signal-independent noise of the device are determined. The mean number of generated charges is determined from the measured mean signal by means of the estimated conversion factor.

Edge injection currents and their effects on 1/ f noise in planar Schottky diodes

A technique has been devised whereby the foreward bias edge current of a planar Schottky diode can be separated from the area current. The saturation current density and ideality factor of this edge current have been measured, the edge saturation current density being related to the area saturation current density by a newly defined edge figure of merit, M e . The area current agrees very closely with the thermionic emission Schottky diode equation, whereas the edge currents exhibit serious departures from this equation. No guard rings or process steps other than those normally used to fabricate diodes are needed to obtain these measurements. An ultra-low-noise preamplifier has been constructed which is sufficiently sensitive to detect the difference between the thermal noise of a short and a 5 ohm resistor. Noise power levels approaching case1 2 kT (pure shot noise) have been observed in unpassivated Schottky diodes. The low frequency noises (1/ f noise) of planar Schottky diodes has been measured and correlated with the edge currents, the correlation being expressed in the form of a newly defined noise figure of merit, M n . The technique and figures of merit are universally applicable to all forms of planar diode structures, including Schottky barrier and diffused junction types.

Position correlations and space-charge noise suppression in solids at low frequencies

Van Vliet and Fassett have settled the pattern for a more direct approach to the current noise problem. This method is applied here to the space-charge-limited current regime in a semiconductor. In this approach, position correlations between carrier concentrations were computed within the Debye-Huckel approximation, and the Green function for the carrier pulse drift on a non-neutral ground was determined with the aid of a specific physical hypothesis (drift without broadening). Noise spectral density distribution functions were computed in closed form for (i) the ideal dielectric diode (without traps) and (ii) the real dielectric diode (with compensated traps) in the limiting cases of very high and very low levels of injection. A space-charge noise suppression effect was found in all cases, except for the trap-compensated solid at very low level of injection. The suppression effect is highly complicated because of the trapping processes and is exerted on the pure shot noise as well as on the generation-recombination noise.

Physical Sources of Noise

Johnson noise is caused by the fluctuation of charges or polarizable molecules in lossy materials. Its magnitude can best be calculated by means of statistical mechanics, which tells us that each degree of freedom must have associated with it an energy of ? kT. This leads to the usual expressions for Johnson noise, including the fact that the available thermal noise power, from a resistor, a lossy network, a lossy dielectric, or an antenna is always kTB. In the case of a resistor, network, or dielectric, T is the temperature of the lossy material. In the case of an antenna, T is the average temperature of the environment which the antenna sees. Consistent with the power kTB available from an antenna, there is a particular density of radiation in space which is a function of temperature and frequency. Noise figure is defined in terms of Johnson noise. Shot noise, due to the discrete nature of electron flow, is generally distinct from Johnson noise, although in some electron devices the expression for the noise in the electron flow has the same form as that for Johnson noise. When the noise in electron flow is greater or less than pure shot noise, the motions of the electrons must be in some degree correlated. In an electron stream of low noise, the random interception of a fraction of the electron flow can reduce the correlation and increase the noise. Johnson noise and shot noise have a flat frequency spectrum.

CXI. A note on the identity of thermal noise and shot noise

Abstract It is shown that the noise in a given frequency range in an ohmic conductor, originally calculated by Nyquist, can be rigorously treated as pure shot noise. Incidentally, a useful new expression kT/Re is obtained, which gives the average direct current in either direction in a circuit of resistance R in temperature equilibrium, if current is carried by elementary charges of magnitude e.

A theory of fluctuation noise

From a consideration of the physical phenomena involved in thermionic conduction and in thermal or Johnson noise, it is deduced that the noise in a space-charge-limited valve is best expressed as a thermal noise, and it is shown that a small correction must be applied to the valve slope resistance to give the value of resistance effective as a noise source. The theoretical temperature of this resistance is then shown to be approximately half the cathode temperature. In a temperature-limited valve, both the resistance and the temperature of the conducting path are indeterminate. The “pure shot noise” formulae are applicable to this case, and represent the maximum noise which can result from the passage of a given current through the system. It is incorrect, however, to state that in space-charge-limited conditions “pure shot noise” is smoothed out, while thermal noise in the internal resistance of the valve appears as an additional factor; shot noise and thermal noise in the valve's internal-resistance are essentially the same phenomenon, but are modified by the differing conditions of electron transit.Nyquist's expression for thermal-agitation noise is derived from the atomic mechanism in the case of a metallic conductor.

A theory of fluctuation noise

From a consideration of the physical phenomena involved in thermionic conduction and in thermal or Johnson noise, it is deduced that the noise in a space-charge-limited valve is best expressed as a thermal noise, and it is shown that a small correction must be applied to the valve slope resistance to give the value of resistance effective as a noise source. The theoretical temperature of this resistance is then shown to be approximately half the cathode temperature. In a temperature-limited valve, both the resistance and the temperature of the conducting path are indeterminate. The “pure shot noise” formulae are applicable to this case, and represent the maximum noise which can result from the passage of a given current through the system. It is incorrect, however, to state that in space-charge-limited conditions “pure shot noise” is smoothed out, while thermal noise in the internal resistance of the valve appears as an additional factor; shot noise and thermal noise in the valve's internal resistance are essentially the same phenomenon, but are modified by the differing conditions of electron transit.Nyquist's expression for thermal-agitation noise is derived from the atomic mechanism in the case of a metallic conductor.