Characteristics of diode temperature sensors which exhibit Mott conduction in low temperature region

Heavily doped silicon diodes of n⁺⁺-p⁺ type which exhibit the Mott temperature dependence of the forward current in a certain range of bias voltages and low temperatures have studied from the point of their use as temperature sensors. In the region of hopping conduction, the operating signal of diodes U (T) (U is a voltage drop across the diode during the passage of a constant current, T is the temperature) reproduces the Mott law (with opposite sign in the exponent), and the temperature sensitivity of such sensors after passing through a minimum (as the temperature is lowered) increases again up to the values typical of room temperatur

A new method of extraction of a p-n diode series resistance from I-V characteristics and its application to analysis of low-temperature conduction of the diode base

A new analytical method of extraction of a diode series resistance from current-voltage characteristics is proposed which takes into account dependence of the series resistance on voltage (or current). The method supposes a presence of linear section in the diode current-voltage characteristic plotted in semi-logarithmic scale. This method is applied here to experimental data for silicon diode in which series resistance is caused by freezing-out free current carriers into impurities at cryogenic temperatures. Character of dependence of the base resistance on electric field in the base layer determined in such way confirms hopping nature of silicon conduction under these conditions

Effect of nonuniform doping profile on thermometric performance of diode temperature sensors

A theoretical investigation of the influence of a nonuniform doping concentration to the temperature response curve of diode temperature sensors is presented, which is the first effort in this field important for diffused diodes used as the temperature sensors. The current-voltage characteristic, from which the temperature response curve can be obtained, has been calculated using the model of a one-dimensional exponentially graded p-n junction with uniformly doped base region and the diffusion current of the minority carriers through the p-n junction. We show that depending on the doping gradient both contributions to the current coming from the electron and hole current components appear to be of the same order of magnitude. That is in contrast to the prediction of the widely used asymmetrical step junction model. It follows from numerical calculations that an effective shift of the temperature response curve due to nonuniformly doped emitter region in the temperature equivalent can reach the value of about 20 K. The limiting temperature Tm in the temperature response curve that restricts its extent into the high temperature range has been analyzed depending on the excitation current, the doping concentration of the base, and the p-n junction depth

Negative magnetoresistance of heavily doped silicon p-n junction

At the liquid helium temperature and under application of magnetic fields up to 9.4 T, a voltage drop across a silicon diode with metallic conductivity of the emitter and base has been measured under passing a constant forward current through the diode. Observed magnetoresistance of the diode is proved as a whole to be extremely small, negative at low fields and changing its sign when the field increases. In the positive region of the diode magnetoresistance, its field dependence is quadratic at first and then becomes close to the linear one. With increase in the current through the diode, the negative component of the diode magnetoresistance decreases, and the smaller its value, the more extended is the quadratic section and the shorter is the linear one. The results are interpreted as caused by hopping conduction over a system of electron “lakes” in the region of p-n junction

Smoothing cubic spline approximation of silicon diode temperature sensors thermometric characteristics

Shown in this paper is the efficiency of a smoothing cubic spline approximation for temperature response curves (TRC) of wide range silicon diode thermometers (SDTs). The offered calculation algorithm allows to describe TRC with a high accuracy and receive the interpolation tables with any temperature step. It allows essentially to expand SDT field of application

Effect of magnetic field on hysteretic characteristics of silicon diodes under conditions of low-temperature impurity breakdown

Effect of magnetic field (up to 14 T) on current-voltage characteristics of silicon n⁺ -p diodes which manifests hysteresis loops related with low-temperature impurity breakdown has been studied. With growth of magnetic field, the hysteresis loops are narrowed and decreased in amplitude and then disappear, but the breakdown continues in a soft form. Planar design of the diode has allowed separating the influence of magnetic field on mobility of the carriers executing impact ionization of the impurities and on the ionization energy itself. Theoretical analysis of the experimental data permitted us to determine the dependence of the ionization energy on the magnetic field. As in other investigated semiconductors, our results demonstrate the dependence of B¹/³ type. A model capable to explain qualitatively the mechanism of suppression of the hysteresis loops by magnetic field is proposed as well

Optimized calibration of cryogenic silicon thermodiodes

Shown in this paper is the efficiency of smoothing cubic spline approximation aimed at optimization of calibration of cryogenic silicon diode thermometers (SDTs). The proposed algorithm allows to significantly reduce time and material costs associated with calibration of SDTs

Nanocrystalline Ge films created by thermal vacuum deposition on GaAs substrates: structural and electric properties

The technique of thermal vacuum deposition of Ge onto GaAs substrates has been used for obtaining nanocrystalline Ge films. Nanocrystalline character of the films is confirmed by atomic force microscopy of their surface and by the data of Raman light scattering. The most probable size of the nanocrystallites forming the films decreases monotonically with decreasing their thickness. Electro conductivity of such the films proves to be high enough (1-10 Ohm·cm at room temperature) and has a character of variable range hopping conduction of Mott’s type. The hops, presumably, take place through the localized states connected with the grain boundaries

Self-consistent method for optimization of parameters of diode temperature sensors

In the framework of the diffusion transport model through an abrupt asymmetric p n-junction, the ideality factor of which is assumed to be equal to unity, and with the help of criteria commonly used to describe theoretically the semiconductor diode structures, the relations are obtained for estimation of parameters of the diode temperature sensor. The set of these parameters provides either the maximum extent of a thermometric characteristic toward the higher temperature range, or maximum sensitivity of the diode temperature sensor. For Ge, Si, GaAs diode temperature sensors with n⁺p- and р⁺n- junctions the limits of thermometric characteristics were determined, together with temperature dependencies of sensitivity, static and dynamic resistance calculated for cases of the maximum length of the thermometric characteristic and of maximum sensitivity. It has been shown that experimentally measured characteristics of diode temperature sensors are within the ranges determined by the limiting characteristics. The ways of further improvement of diode temperature sensors are discussed

Non-ohmic Mott conductivity and thermometric characteristics of heavily doped silicon structures

We investigated I-V curves and thermometric characteristics of heavily doped p-silicon structures at liquid helium temperatures. The variable-range hopping conductivity is shown to occur in the structures studied. The obtained parameters of non-ohmic Mott conductivity and their temperature and electric field dependencies enabled us to explain the features in structure thermometric characteristics. It is shown that both height and position of the responsivity peak depend on the extent to which the hopping conductivity is non-ohmic. They are essentially determined by the density of states near the Fermi level