Alloy Transistors Research Articles

Characteristics of Amorphous Silicon Based Alloy Field Effect Transistors

ABSTRACTWe have developed a new theory to describe the current-voltage characteristics of amorphous silicon based alloy field effect transistors. We show that the transition from below to above threshold operation occurs when the Fermi level in the accumulation region moves from the deep to tail localized states in the energy gap and that the field effect mobility is dependent on gate voltage. We also propose a new technique to determine the flat-band voltage from the I-V characteristics in the below threshold regime.

Frequency Response of Alloy Junction Transistors in the Inverse Mode of Operation

Frequency Response of Alloy Junction Transistors in the Inverse Mode of Operation

The first decade of transistor development: a personal view

The development of the junction transistor from its earliest form of a plastics encapsulated, alloy transistor to the final silicon planar device is traced during the period from 1952 to 1962. At the same time some of the significant steps in the development of the understanding of the device are described.

Effects of surface recombination and geometry in alloy junction transistors

Collector to base current amplification factor (α cb ) in alloy junction transistors has been studied as a function of surface recombination velocity (S) for the case where emitter is bigger than the collector. Calculations have been done for transistors with collector diameter varying from 0·005 cm to 0·07 cm and emitter to collector radius ratio ( b/ a) from 2 to 10. The ratio of normal and inverse amplification factors (α N /α I ) has been calculated as a function of ‘ S’ and has been compared with the experimental observations of Moore and Pankove [2].

The influence of high current densities on the avalanche breakdown characteristics of bipolar transistors†

This paper is concerned with the effects of large current densities upon the common emitter breakdown characteristics of both epitaxial and alloyed junction transistors, although the arguments may be equally applied to devices fabricated by other techniques. The stability of the active conducting area is considered as well as the interrelation of the three variables, current density, collector voltage and carrier multiplication in the collector depletion region. Results are discussed with relation to observed oscillations between the second breakdown mode and the avalanche mode. The theories of Kirk have been employed in a modified form to obtain general expressions for the movement of depletion layer boundaries under high current conditions. Comparison is drawn between the conflicting hypotheses of Kirk and van der Ziel, and the respective consequences of their theories on high current second breakdown are investigated.

Effect of non-uniform emitter current distribution on power transistor stability

The concentration of current to the edges of an emitter in a power transistor is known to be due to the transverse voltage drop along the emitter face caused by base current flow. The calculation of this ‘crowding’ phenomenon is usually made assuming an isothermal emitter surface. It is shown that in general, when a transistor is dissipating power, that the emitter current can crowd either to the center portion or edge of the emitter, depending on the value of operating collector voltage and current. The non-uniform current distribution results from a temperature peak at the center of the emitter causing a concentration of current to the emitter center; this is counteracted by the transverse base voltage drop causing crowding to the emitter edge. The effect of this non-uniform emitter current distribution on transistor thermal stability is investigated for two transistor designs—one simulating an alloy transistor and the other a diffused-base transistor. The results indicate that the wide-base alloy device is more stable for a given power level. Values of external emitter or base resistance necessary for thermal stabilization at high power levels are calculated for the two different transistor designs. In both cases for a given power level, stabilization is more easily achieved at high current, low collector voltage rather than low current, high voltage.

Minority Carrier Distribution in the Base Region of Alloy Junction Transistors

This paper presents an expression for the three dimensional distribution of minority carriers in the base region of alloy junction transistors for the case when the emitter is bigger than the collector. This expression has been successfully used for deriving a relation for the current amplification factor, αcb Such an expression is of basic importance when we want to calculate the ‘inverse alpha’ (value of αcb when the roles of collector and emitter are interchanged). The relation for αcb shows that as the ratio of collector to emitter radii is increased αcb will increase, which is in accordance with the experimental observations of Moore and Pankove.

Current dependence of collector junction capacity of alloy junction transistor under inverse operating condition

Current dependence of collector junction capacity of alloy junction transistor under inverse operating condition

Diffusion of Minority Carriers in the Base Region of an Alloy Junction Transistor in the Presence of a Magnetic Field

This paper reports the study of the nature of diffusion of minority carriers in the base region of an alloy junction transistor in the presence of a magnetic field. It has been experimentally observed that the diffusion constant of minority-carrier holes in a p-n-p type transistor is decreased in magnetic field and the magnitude of the decrement varies with the injected carrier density, being larger at higher injection levels. The relative change in diffusion constant shows a linear variation with the magnetic field intensity, contrary to the quadratic theory for isotropic semiconductor. The results have been explained by taking into consideration the effect of inhomogeneities due to concentration gradients and Hall perturbation effect given by Landauer and Swanson on the diffusion of carriers in the presence of magnetic field.

Noise and instability of germanium alloy transistors

Noise and instability of germanium alloy transistors

The analogue computer simulation of an alloy junction transistor wide band equivalent circuit

The paper reviews and develops an accurate equivalent circuit of a junction transistor which is valid over a wide band of frequencies; the parameters of the circuit themselves emphasizing the physical mechanisms of the device. It is then shown that the equations governing the equivalent may be solved by a general purpose analogue machine. After establishing the accuracy of the analogue by comparing its results with those from a digital machine. The problem of adjusting the parameters of the analogue so as to obtain accurate transistor representation is discussed briefly.

A characterization technique for second breakdown in Ge alloyed junction transistors

A characterization technique for second breakdown in Ge p-n-p alloyed junction transistors with the open base condition is described. This method is based on the saturated characteristics which are expressed in the form of exponential dependence on the slope of the rising part of the applied voltage. Using this method, a comparison is made of transistor SB characteristics in terms of device characteristics, such as BV CEO and H FE .

Determination of Some of the Physical Parameters of Alloy Junction Transistors

ABSTRACTBy measuring the low frequency current amplification factor and the hybrid parameters in the common emitter configuration a sufficiently accurate method of evaluating some physical parameters of a uniform base alloy junction transistor is described. By plotting h12e versus h22e/Ie an accurate method of evaluating the junction temperature and by measuring the applied base emitter voltage at various emitter currents, a new method of evaluating the conducting cross-section are given. The transition capacitances at both emitter and collector junctions are also calculated. The method is applicable at low injection levels only.

Determination of Physical Parameters of a Junction Transistor

The paper deals with a new method of determining some of the physical parameters of alloy junction transistors. From a measurement of the variation of common emitter input impedance and the current amplification factor, with emitter current, a method of calculating base spreading resistance and the junction temperature is given. Using in addition the measured values of the base-emitter voltages at different emitter currents, a method of calculating the carrier densities in the base region, emitter efficiency and recombination term is also given. A simple experimental set up used for these measurements is described. The method is applicable only to uniform base germanium transistors.

Solder ball formation in silicon alloy transistors

This paper discusses the investigation and solution of the so-called problem which has plagued the transistor industry for years. Upon investigating silicon alloy transistors which use tin for electrodes, it was discovered that solder balls (which can cause internal short circuiting of the device) are not necessarily associated with manufacturing procedures as previously believed but are produced by the devices themselves because of the material used in construction. Electrical stresses or low temperatures produce balls in units which were initially free of any foreign matter. This is due to the low-melting-temperature tin alloy used in the construction of the transistor (or other semiconductor). Thus, devices may have balls when put in use and cause equipment failure later. The devices appear good under all measurement; however, when the devices are in use, a mechanical short circuit may shake a ball loose, short circuiting the transistor and making the circuit inoperable.

"Solder ball" formation in silicon alloy transistors

The authors have found that formation of "solder balls" may not be due to any foreign matter in the package but instead be a characteristic of this type of device when: a) Local hot spots develop as the result; b) temperatures rise in excess of 23O°C,; c) during life testing or "burn-in." The devices which were extensively studied in this investigation were highpower silicon alloy-diffused transistors and high-reliability medium-power silicon alloy transistors. The five conclusions reached from this work are the following. 1) Balls are formed as a result of temperature in excess of 230°C (melting point of tin). 2) These temperatures are reached either by electrically induced hot spots or by external heating of the device. 3) Analysis of the balls has shown it to be 99% tin, which is the main ingredient of the emitter and base regions. 4) Electrical parameters initially are not degraded by formation of balls. 5) The balls are physically attached to the device until mechanically jolted loose. The ball problem has been found in this type of silicon alloy transistor and could be a principal mode of failure in this device. Balls have not been found in other types of silicon transistors, such as planar or mesa transistors.

Calculation of Electrical and Radiation Storage Time in Transistors

The conventional viewpoint of saturation in junction transistors, from a device point of view, considers the excess minority carriers in the base region. A different viewpoint considers the majority carriers in the base. The important elements then are the number of these carriers stored in the transistor and whether they are stored in the active base region, the extrinsic base region, the collector body, or the epitaxial layer. The storage of carriers in the active base region plays a relatively minor role in the storage effect for most modern transistors because of the small volume of semiconductor material involved. In alloy, diffused, and epitaxial transistors the storage of carriers (electrons in a PNP transistor) is shown to be in the last three regions named above, respectively; in none of these transistor types is the storage region identifiable as the active base region. This new viewpoint leads to well-accepted storage-time expressions for alloy and diffused transistors and to new storage-time expressions for epitaxial transistors. Detailed calculations of the primary photocurrent have been made for three practical transistor construction types that relate this current to basic device parameters and to the electrical storage time. In addition, the radiation storage time has been calculated in terms of the electrical storage time for epitaxial transistors. Examples of these calculations are given and the results presented.

Investigation of the current gain of a composite transistor

An expression is derived for the complex current gain of a composite transistor. It is shown that the current gain of a composite transistor is influenced by the low-frequency current gain and cutoff frequency of the individual transistors. The emitter and collector depletion-layer capacitances and the extrinsic base resistances are also shown to influence the current gain of a composite transistor. It is found that there is a considerable difference between the current-gain characteristic of a composite transistor predicted by the equation for α based on one-dimensional diffusion theory and that predicted by the first-order approximation. Measurements are made of the steady-state frequency response and the transient response of a composite transistor constructed from two alloy-junction transistors of the same polarity. Close agreement is found between the measured characteristic and the characteristic predicted by the equation for α based on one-dimensional diffusion theory where the effects of extrinsic components have been taken into account.

Period Stabilization of Timing Multi–vibrators†

ABSTRACT The problems of instability of periods and pulse lengths of transistor timing multi-vibrators are reviewed. A modified monostable multi-vibrator with improved charaecteristics in freedom from jitter and better temperature stability is described. This uses germanium alloy transistors with a complementary type silicon transistor in grounded base configuration as a constant current source through which the timing capacitor discharges. In addition a silicon diode effectively isolates the timing network during timing interval. A feature of the circuit is the linear voltage waveform obtainable and its useful applications with suitable modifications are as a linear delay circuit or as an analogue-to-digital converter of high accuracy.

Measurement of avalanche multiplication of injected holds in germanium p-n-p diffused-base transistors

A three-terminal dc measurement is made of avalanche multiplication of holes injected from the emitter into the collector junction of diffused-base germanium p-n-p transistors. The method is applicable to asymmetric thin-base transistors at currents at which dc base current is independent of base width when emitter to base voltage (V EB ) is held constant. Injected collector current and V EB are measured at constant emitter current as a function of collector to base voltage (V). V EB is measured to take base narrowing into account. Collector reverse current is balanced out. The advantages of this method over two-terminal measurements are that surface, space-charge recombination and internal field emission currents are balanced out and no a priori assumption of the form of the multiplication factor M(V) is needed. For collector barriers which are nearly step n^{+}p junctions with the p-type resistivity in the neighborhood of 1 ohm-cm, the multiplication data, which cover the range 1.05 \siml M \siml 2.0 , fit the Miller equation M^{-1} = 1 - (V/V_{B})^{n} n = 3.2 \pm 0.2 in agreement with Miller's two-terminal measurements using alloy and grown-junction Ge transistors. The parameters V B from extrapolation of the present data agree within experimental error of five per cent with the collector diode breakdowns BV CBO measured by Miller. However, in the present measurements on diffused-base transistors, appreciable surface current multiplication occurs with the result that BV CBO measured at 1 ma is approximately 18 per cent less than V B . The absence of microplasma noise in the multiplied injected hole current indicates that multiplication occurs uniformly in the collector barrier under the emitter at least to M = 2 .