Temperature Dependence Of Current Gain Research Articles

Temperature dependence of current gain in 4H-SiC bipolar junction transistors

The temperature dependence of current gain from 140 to 460 K in 4H-SiC bipolar junction transistors (SiC BJTs) was investigated. The current gain increased from 110 to 1200 with decreasing temperature from 460 to 200 K. The high current gain at the low temperature can be ascribed to the enhanced incomplete ionization of aluminum acceptors in the base layer, resulting in the increase in injection efficiency. However, when the temperature was further reduced from 200 to 140 K, the current gain decreased from 1200 to 515, which is caused by high injection condition in the base layer, because of a very low hole concentration below 200 K.

Design and optimization of Ge profiles for improved thermal stability of SiGe HBTs

The impact of the three state-of-the-art germanium (Ge) profiles (box, trapezoid and triangular) across the base of SiGe heterojunction bipolar transistors (HBTs) under the condition of the same total amount of Ge on the temperature dependence of current gain β and cut-off frequency fT, as well as the temperature profile, are investigated. It can be found that although the β of HBT with a box Ge profile is larger than that of the others, it decreases the fastest as the temperature increases, while the β of HBT with a triangular Ge profile is smaller than that of the others, but decreases the slowest as the temperature increases. On the other hand, the fT of HBT with a trapezoid Ge profile is larger than that of the others, but decreases the fastest as the temperature increases, and the fT of HBT with a box Ge profile is smaller than that of the others, but decreases the slowest as temperature increases. Furthermore, the peak and surface temperature difference between the emitter fingers of the HBT with a triangular Ge profile is higher than that of the others. Based on these results, a novel segmented step box Ge profile is proposed, which has modest β and fT, and trades off the temperature sensitivity of current gain and cut-off frequency, and the temperature profile of the device.

Temperature Dependence of Current Gain, Ideality Factor, and Offset Voltage of AlGaAs/GaAs and InGaP/GaAs HBTs

This paper elucidates the stabilities of the dc current gain, ideality factor, and offset voltage against variations in temperature and currents for GaAs-based heterojunction bipolar transistors (HBTs). The InGaP/GaAs HBT markedly reduces the offset voltage and improves the temperature stability of the dc current gain relative to those of AlGaAs/GaAs benchmark devices. The relative insensitivity of the offset voltage in the InGaP/GaAs HBT to the temperature is established by comparison with AlGaAs/GaAs counterparts. One of the more intriguing aspects of these two HBTs is the replacement of the AlGaAs emitter with the InGaP emitter to improve the temperature stability of the offset voltage. Specifically, the effect of the base current on the offset voltage is abnormal in these devices. In this paper, the conventional Ebers-Moll model cannot account completely for our observed phenomena. Accordingly, the results herein (improved temperature stability of the offset voltage in the InGaP emitter HBT and the uncommon base current effect in these two devices) are interpreted in terms of a physics-based analytical model. A strong consistency existed between the experimental data and the theory. Additionally, some reasonable predictions (not obtained from the measured data) of the specific physically based model are presented. The large-signal model provides a description of device performance that will be of use to device engineers and designers.

Temperature dependence of current gain of InGaP/InGaAsN/GaAs heterojunction bipolar transistors

The temperature effect on current gain is presented for InGaP/InGaAsN/GaAs heterojunction bipolar transistors (HBTs) including as-grown and annealed HBTs. The annealed HBT was annealed before device fabrication at 700 °C for 30 sec. Experimental results showed that the current gains of the annealed HBT increase with the increase of temperature in the temperature range of –20–100 °C . The smaller the collector current, the larger is the positive differential temperature coefficient. At high current levels, the current gain dependence on temperature is significantly reduced. On the other hand, a negative coefficient is observed in the as-grown HBT in all current range. This finding indicates that the annealed InGaP/InGaAsN/GaAs HBT is better candidate than the as-grown InGaP/InGaAsN/GaAs HBT for power devices. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Characterization of InGaP/GaAs Heterojunction Bipolar Transistors with a Heavily Doped Base

Characteristics of InGaP/GaAs heterojunction bipolar transistors (HBTs) with a heavily doped base are examined at the base doping level NB ranging from 5×1019 to 5×1020 cm-3. At NB of less than 3×1020 cm-3, the current gain is mainly determined by Auger recombination in the intrinsic base region and is inversely proportional to the square of NB. In contrast, the current gain at NB above 3×1020 cm-3 is significantly decreased. We evaluated the effective barrier height of holes between the emitter and the base by measuring temperature dependence of current gain, and found that the effective hole barrier is reduced as NB increases. This result is explained by the large energy shift of the Fermi level inside the valence band due to heavy doping, causing the increase in the back injection of holes into the emitter, and thus reducing the current gain.

Temperature-dependent study of a lattice-matched InP/InGaAlAs heterojunction bipolar transistor

In this work, we report the temperature-dependent characteristics of a new InP/InGaAlAs heterojunction bipolar transistor (HBT). In order to improve the dc performance of conventional InGaAs-based single HBTs, the quaternary In/sub 0.53/Ga/sub 0.34/Al/sub 0.13/As with a wider bandgap is employed as the material for both the base and collector layers. Experimentally, the studied device exhibits a relatively high common-emitter breakdown voltage and low output conductance even at high temperature. Based on the breakdown mechanism of avalanche multiplication, the negative temperature dependence of breakdown voltage is attributed to the positive temperature-dependent impact ionization coefficient. Furthermore, the temperature dependence of current gain is investigated and reported. It is believed that the suppression of hole injection current with decreasing temperature is responsible for the opposite variation of current gains at high current levels.

Modeling of current gain's temperature dependence in heterostructure-emitter bipolar transistors

The temperature dependence of the current gain is investigated for GaAs-based heterostructure-emitter bipolar transistors (HEBT's). With the separation of the p-n junction and the heterojunction, the mechanism of hole injection from the base to emitter in the HEBT is different from that of a conventional HBT. Theoretical results demonstrate that the thermionic emission current plays an important role for the hole current which results in a smaller negative or even positive temperature coefficient for the current gain. Experimental data show that the base current for HEBTs is indeed dominated by thermionic emission as predicted. This finding indicates that the HEBT structure is the suitable choice for high power and high speed applications.

Temperature dependence of current gain of GaInP/GaAs heterojunction and heterostructure-emitter bipolar transistors

The temperature effect on current gain is presented for GaInP/GaAs heterojunction and heterostructure-emitter bipolar transistors (HBTs and HEBTs). Experimental results showed that the current gain of the HEBT increases with the increase of temperature in the temperature range of 25-125/spl deg/C and decreases slightly at temperatures above 150/spl deg/C. The smaller the collector current, the larger is the positive differential temperature coefficient. At high current levels, the current gain dependence on temperature is significantly reduced. On the other hand, a large negative coefficient is observed in the HBT in all current range. This finding indicates that the HEBT is a better candidate than the HBT for power devices.

Analysis of the temperature dependence of current gain in heterojunction bipolar transistors

An analytical description is developed which highlights the important physical parameters influencing the temperature dependence of the current gain in heterojunction bipolar transistors (HBTs). Each of the possible base current components is discussed and its relative importance to temperature dependence is assessed. The manifold nature of the contributions explains the widely different conditions under which negative differential resistance has been previously reported. Space charge region recombination is found to be the main contribution to temperature variation of current gain at low current densities. Factors affecting modern highly doped base devices at high current densities and elevated temperatures are reverse hole injection and base bulk recombination.

A high-current-gain low-temperature pseudo-HBT utilizing a sidewall base-contact structure (SICOS)

A silicon pseudo-heterojunction bipolar transistor (HBT) with a current gain of over 100 at 77 K has been successfully fabricated using the upward operation of a self-aligned sidewall base-contact structure (SICOS). The measured characteristics agree well with the theoretical prediction, showing a negative exponential temperature dependence of current gain and a 2500-times larger collector current than in the conventional transistor at 77 K. This makes homojunction bipolar transistor operation at low temperatures feasible and has the potential to overcome the bipolar/BiCMOS limitations. >

Silicon bipolar transistors with negative and positive current gain temperature dependence and output conductance on the same monolithic chip

Silicon bipolar transistors with negative and positive current gain temperature dependence and output conductance on the same monolithic chip

Temperature dependence of current gain in AlGaAs/GaAs heterojunction bipolar transistors

Details of the temperature dependence of current gain in AlGaAs/GaAs heterojunction bipolar transistors (HBT’s) are reported for the first time. Unlike homojunction transistors, the gain initially increases with decreasing temperature from 425 K followed by a decrease towards 77 K at a temperature which is dependent on AlAs mole fraction in the emitter. Variation of gain with temperature is much smaller than what is normally seen in homojunction transistors adding another advantage in favor of the HBT’s. Hole injection current into the emitter and parasitic recombination currents are shown to be the reasons for the observed temperature dependence of gain.

A contribution to the current gain temperature dependence of bipolar transistors: H.-M. Rein, H. v. Rohr and P. Wennekers Solid-St. Electron., 21, p.439 (1978)

A contribution to the current gain temperature dependence of bipolar transistors: H.-M. Rein, H. v. Rohr and P. Wennekers Solid-St. Electron., 21, p.439 (1978)

A contribution to the current gain temperature dependence of bipolar transistors

In this paper it is demonstrated by a simple calculation that the temperature dependence of current gain may be significantly influenced by both the different freeze-out rates of mobile carriers in emitter and base and the different temperature dependences of mobilities in these two regions. These effects can considerably reduce the decrease of current gain towards low temperatures, caused by the effective bandgap difference between the emitter and base region.

A contribution to the current gain temperature dependence of bipolar transistors : H.-M. Rein, H. v. Rohr and P. Wennekers. Solid-St. Electron.21, 439 (1978)

A contribution to the current gain temperature dependence of bipolar transistors : H.-M. Rein, H. v. Rohr and P. Wennekers. Solid-St. Electron.21, 439 (1978)

Comparison of one- and two-dimensional models of transistor thermal instability

The I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</inf> -V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CE</inf> locus predicted by a one-dimensional model of thermal instability is compared with the I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</inf> -V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CE</inf> locus predicted by a numerical model which accounts for nonuniform heat generation over the transistor area and also two-dimensional heat flow within the heat sink. Both models include the effects of distributed emitter and base ballast resistance, as well as the magnitude and temperature dependence of current gain. An important result obtained from this comparison is that the I-V loci predicted by the two models are very nearly the same, even though the temperature and power density profiles over the transistor die are distinctly different. It is the I-V locus which is of most practical interest, since it is one portion of the boundary of the forward safe operating area (SOA). The similarity of the I-V loci should allow one to use the simple one-dimensional model to predict a particular SOA, even though the assumptions under which the model was originally derived are not valid at the onset of thermal instability. Confirmation of this approach has been obtained by demonstrating good agreement between the measured safe operating area and that predicted by the one-dimensional model for both single- and double-diffused transistors. The predicted improvement due to the addition of discrete emitter resistors has also been verified by SOA measurements on actual devices. The device parameters which are important in determining SOA are the effective emitter and base resistances, the magnitude and temperature dependence of current gain, and the effective thermal resistance between the active region of the transistor and its heat sink. The quantitative dependence of SOA due to each of these parameters is described.

Investigation of current-gain temperature dependence in silicon transistors

This paper presents the results of an investigation of the factors influencing transistor current-gain temperature dependence. Phase one of the investigation demonstrated experimentally that current-gain temperature dependence is an inverse log function of the average active base resistivity. Devices were found to be less temperature sensitive with lighter base doping levels. Phase two of the investigation experimentally demonstrated current-gain temperature dependence to be an inverse exponential function of the emitter doping level. This large temperature dependence is shown to be a possible consequence of an emitter band-gap decrease, presumably caused by the large number of dislocations and lattice deformations at high doping levels. Using the predicted techniques, several runs of epitaxial planar devices were fabricated which had practically no current-gain temperature dependence, and suffered no noticeable loss in other parameters. Current-gain temperature dependence is also thought to be one of the contributors to hot-spot formation and secondary breakdown. To determine if secondary-breakdown capability had been increased, these temperature-insensitive devices were tested to forward secondary breakdown and compared to standard products of the same geometry. The temperature-independent devices were able to withstand a 40-percent increase in operating power before the onset of secondary breakdown. This increase in capability is thought to be the result of less tendency toward hot-spot formation due to decreased thermal regenerative action.

Displacement Damage in Silicon and Germanium Transistors

An experimental and theoretical analysis of neutron damage to germanium and silicon transistors is presented. A combination of experimental data and first order theory has been used to determine lifetime damage constant as a function of neutron energy. Two separate effects attributable to the recombination centers have been identified. At low bias levels recombination centers present in the emitter diode field region cause a very large decrease in current gain. At higher levels of emitter bias current recombination centers present in the base region cause a reduction in current gain. The temperature dependence of current gain is stronger when emitter region recombination is the dominant process than when base region recombination is most effective. The damage thresholds of silicon transistors can be increased by operating at high ambient temperatures. The characteristics of the recombination centers have been determined from the experimental data and agree well with values previously obtained by measurements on bulk semiconductor samples. Two discrete recombination levels in silicon and two discrete recombination levels in germanium are shown to determine the dependence of transistor current gain on neutron radiation.