James W. Holm‐Kennedy

Energy relaxation of electrons in the (100) n-channel of a Si-MOSFET: II. Surface phonon treatment

Abstract Electron energy relaxation is studied in the n-channel of a (100) surface silicon MOSFET device as a function of an “electron temperature” T e at 4.2K lattice temperature. The phenomenological energy relaxation time τ e ( T e ) is determined theoretically and then compared to the experimental value in order to ascertain which scattering mechanism(s) may be active in the n-channel. A method for treating three dimensional transport with bulk phonon scattering under band bending conditions at the surface is presented. This method should be appropriate for MOSFETs under weak inversion conditions as well as for JFETs and Schottky FET devices. Two analytical treatments are presented: (1) Non-degenerate model which assumes that the electron distribution is correctly characterized by Maxwell-Boltzmann statistics; and (2) A general degenerate model employing Fermi-Dirac statistics and accounting for the band edge bending. Although the analysis should be most appropriate for cases where subbanding is not present or is not pronounced, the models are applied to experimental results for an n-channel MOSFET device (where subbanding is to be expected). Surprisingly good agreement between theory and experiment is achieved when a single bulk 42.5 activation temperature phonon is assumed responsible for the electron energy relaxation in the n-channel at low lattice temperatures.

Experimental determination of highly concentration‐sensitive effects of intervalley electron‐electron scattering on electric‐field‐dependent repopulation in n‐Si at 77 K

Measurements have been made of current density versus electric field on and oriented samples of n‐Si at 77 K with resistivities ranging from 0.050 to 200 Ω cm. These have been analyzed to yield the concentration and field dependence of repopulation resulting from a application of electric field. The magnitude of the repopulation has been found to be extremely sensitive to the free‐carrier concentration. This sensitivity is attributed to the energy exchange effects of intervalley electron‐electron scattering. The repopulation provides a new and highly selective experimental parameter for use in the study of electron‐electron scattering in semiconductors.

Warm‐Carrier dc Transport in n Si

Measurements of the dc current density at 77 °K lattice temperature vs electric field for 26‐Ω cm n Si are presented and analyzed to determine the amount of repopulation when the field is applied in the 〈100〉 and 〈110〉 crystallographic directions. A relatively simple and straight‐forward technique for computing the energy‐relaxation‐time dependence on the electric field is proposed and applied to n Si. The electron temperatures vs electric field for several differently oriented conduction‐band minima are also calculated. An explanation for the previously observed but unexplained decrease in amount of repopulation above 400 V/cm is given. A new technique for computing the theoretical repopulation‐field dependence is also presented and found to give excellent agreement with the experimental results. A theory similar to that used in past literature, but more general, is used in the following experimental determination of the warm‐carrier repopulation in n Si.

Effect of electron‐electron and impurity scattering on hot electron repopulation in n‐Si at 77 K

The transport roles of electron‐electron (e‐e) and intravalley impurity scattering (neutral and ionized) in n‐Si at 77 K were studied under high‐electric‐field (0–3000 V/cm) nonequilibrium conditions, by comparing the theoretical and experimental ratio of 〈111〉 to 〈100〉 field‐dependent conductivity over a range of free‐electron concentrations that fully encompasses this ratio’s variation with concentration (2×1013–2×1016 cm−3). Theoretical calculations were performed using a numerical technique which allows an ’’exact’’ solution to the Boltzmann transport equation. Electron‐electron scattering was included in the calculation using the Fokker‐Plank formulation. It was found that e‐e scattering was primarily responsible for the decrease in the conductivity ratio with increasing concentration through its effect on repopulation; both intravalley and intervalley e‐e scattering were found to be important. Neutral impurity scattering also had a significant effect on repopulation. An apparent increase in free‐ele...

A Technique for Measuring Nonsquare Pulsed High Voltages to ±0.25% Accuracy

An accurate technique (≤±1/4% error) for measuring a wide range of pulsed voltages and currents of large magnitude (kilovolts and amperes) and short duration at either low or high repetition rates is described. The technique is accurate for both square and nonsquare pulses. The technique is particularly useful for measuring the J‐E characteristics (current density‐electric field) of semiconductors at high electric fields. The unknown voltages are matched on a CRO to voltage‐divided Zener diode limited pulses which are accurately known. The sample circuit and reference pulse circuits are given. The accuracy of the technique is demonstrated over a wide voltage and current range. Operating and construction precautions are listed for the convenience of the reader.

OBSERVATION OF MICROWAVE REPOPULATION MODULATION IN n‐Si AT 77 °K

The microwave (9.61 GHz, dielectric constant of n‐Si was measured as a function of crystallographic orientation and as a function of applied dc electric field (warm electron conditions) at 77 °K lattice temperature. The dielectric constant was found to be anisotropic. An analysis of the results correlated with the observed free carrier repopulation shows a new contribution to the microwave properties. This contribution arises from a repopulation modulation at the microwave frequency.

N‐type switching erroneously attributed to field‐enhanced trapping

N‐ or S‐type switching in the I‐V characteristics of semiconductor resistive bars immersed in liquid nitrogen occur if the I2R power per surface area generated in the semiconductor exceeds a certain threshold value. Such switching has been consistently misinterpreted and attributed to field‐enhanced trapping. This communication briefly explains the thermal switching, identifies numerous errors in the literature, and describes an experiment to distinguish bertween thermal and electronic switching.

Observation and explanation of multistable nonvolatile memory in silicon FIT diodes

Point‐contact, Schottky, and diffused‐silicon diodes doped with copper and iron impurities have been fabricated. These diodes show multistable behavior at room temperature, exhibiting a wide range of easily discriminated nonvolatile I‐V rectifying characteristics (class I behavior). The class I behavior is explained in terms of field‐induced trapping (FIT) with stationary space‐charge domain formation in or near the depletion region. If the class I devices are treated by heating with a large current pulse‐i.e., if they are formed‐a second class (class II) of multistable behavior is observed. The class II behavior is also observed in Au‐doped devices and is not presently well understood.