Dependence Of Current Gain Research Articles

Electrical performance of 130 nm PD-SOI MOSFET with diamond layout

Some special effects of SOI devices with diamond layout are analyzed in this paper based on the silicon data from 130 nm PD-SOI T-gate MOSFET. LCE and PAMDLE induced current gain dependence on geometry parameters of devices with fixed gate area and fixed smallest channel lengths are presented. BVDS of different diamond devices are studied and discussed and a specified geometry has been found with better BVDS performance. For the special shape of channel region, the hot-carrier effect induced body current is collected in the experiment and the mechanism of body current increasing has been analyzed theoretically.

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.

Analysis of the electrical characteristics of GaInP/GaAs HBTs including the recombination effect

An analytical model is used to predict the effects of surface recombination current on the gain and transit time of GaInP/GaAs heterojunction bipolar transistors (HBTs). The present analysis shows that consideration of the recombination current gives current gain values that are comparable to those of the experimental results. The dependence of current gain on temperature, base doping and emitter area are also analyzed, and the variation in collector current with emitter-base voltage, temperature and doping is considered.

Removal of Crystal Orientation Effects on the Current Gain of 4H-SiC BJTs Using Surface Passivation

In this letter, the dependence of current gain and base resistance on crystal orientations for single-finger 4H-SiC bipolar junction transistors (BJTs) is analyzed. Statistical evaluation techniques were also applied to study the effect of surface passivation and mobility on the performance of the devices. It is shown that BJTs with an emitter edge aligned to the [1210] direction shows a lower current gain before surface passivation and higher base resistance after contact formation compared with other investigated crystal directions. However, the devices show a similar current gain independent of the crystal orientation after surface passivation.

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.

Current Gain Dependence on Emitter Width in 4H-SiC BJTs

This paper reports the fabrication of epitaxial 4H-SiC bipolar junction transistors (BJTs) with a maximum current gain β=64 and a breakdown voltage of 1100 V. The high β value is attributed to high material quality obtained after a continuous epitaxial growth of the base-emitter junction. The current gain of the BJTs increases with increasing emitter width indicating a significant influence of surface recombination. This “emitter-size” effect is in good agreement with device simulations including recombination in interface states at the etched termination of the baseemitter junction.

Influence of Lattice Constants of GaN and InGaN on npn-Type GaN/InGaN Heterojunction Bipolar Transistors

We investigated the a- and c-axis lattice constants of GaN buffer and 180-nm-thick p-InGaN layers grown on SiC and sapphire substrates using reciprocal space mapping of the X-ray diffraction intensity. It was found that the a-axis lattice constant of the GaN buffer layer on a SiC substrate is larger than those of unstrained GaN and a GaN buffer layer on a sapphire substrate. As a result, the p-InGaN layer on GaN/SiC is fully strained even at the In mole fraction of 9.0% where that on GaN/sapphire is relaxed. This result means that fewer defects are generated in p-InGaN on GaN/SiC at higher In mole fractions. This is another advantage of SiC substrate for npn-type GaN/InGaN heterojunction bipolar transistors, in addition to its high thermal conductivity. The collector current density dependence of current gain shows the ideality factor of 2 for GaN/InGaN HBTs on both SiC and sapphire substrates. This is ascribed to the recombination current at the emitter-base interface, which arises from the threading dislocations generated at the interface between the substrate and nitride buffer layer.

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.

Current gain dependence on subcollector and etch-stop doping in InGaP/GaAs HBTs

The DC current gain dependence of InGaP/GaAs heterojunction bipolar transistors (HBTs) on subcollector and etch-stop doping is examined. Samples of InGaP/GaAs HBTs having various combinations of subcollector doping and etch-stop doping are grown, and large area 60 /spl mu/m/spl times/60 (/spl mu/) HBTs are then fabricated for DC characterization. It is found that the DC current gain has a strong dependence on the doping concentration in the subcollector and the subcollector etch-stop. Maximum gain is achieved when the subcollector is doped at 6/spl sim/7/spl times/10/sup 18/ cm/sup -3/ while the subcollector etch-stop is doped either above 6/spl times/10/sup 18/ cm/sup -3/ (current gain/sheet resistance ratio, /spl beta//R/sub b/=0.435 at I/sub c/=1 mA) or below 3.5/spl times/10/sup 17/ cm/sup -3/ (/spl beta//R/sub b/=0.426/spl sim/0.438 at I/sub c/=1 mA). The data show that it is not necessary to heavily dope the subcollector etch-stop to reduce the conduction barrier and to obtain high current gain. The high current gain obtained with the low InGaP etch-stop doping concentration is attributed to the reduction of the effective energy barrier thickness due to band bending at the heterojunction between the InGaP etch-stop and the GaAs subcollector. These results show that the /spl beta//R/sub b/ of InGaP/GaAs HBTs can improve as much as 69% with the optimized doping concentration in subcollector and subcollector etch-stop.

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.

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.

Role of neutral base recombination in high gain AlGaAs/GaAs HBT's

Neutral base recombination is a limiting factor controlling the maximum gain of AlGaAs/GaAs HBT's with base sheet resistances between 100 and 350 /spl Omega///spl square/. In this work, we investigate five series of AlGaAs/GaAs HBT growths in which the base thickness was varied between 500 and 1600 /spl Aring/ and the base doping level between 2.9/spl times/ and 4.7/spl times/10/sup 19/ cm/sup -3/. The dc current gain of large area devices (L=75 /spl mu/m/spl times/75 /spl mu/m) varies by as much as a factor of two at high injection levels for a fixed base sheet resistance, depending on the growth optimization. One of these series (Series TA) has the highest current gains ever reported in this base sheet resistance range, with dc current gains over 225 (@ 200 A/cm/sup 2/) at a base sheet resistance of 330 /spl Omega///spl square/. A high dc current gain of 220 (@ 10 kA/cm/sup 2/) was also confirmed in small area devices (L=8 /spl mu/m/spl times/8 /spl mu/m). High-frequency tests on a separate set of wafers grown under the same conditions indicate these high current gains can be achieved without compromising the RF characteristics: Both high and normal gain devices exhibit an f/sub t//spl sim/68 GHz and f/sub max//spl sim/100 GHz. By fitting the base current as a sum of two components, one due to recombination in the neutral base and the other in the space charge region, we conclude that an improvement in the minority carrier lifetime is responsible for the observed increase in dc current gain. Moreover, we observe a thickness-dependent variation in the effective minority carrier lifetime as the gains increase, along with a nonlinear dependence of current gain on base doping. Both phenomena are discussed in terms of an increase in Auger and radiative recombination relative to Hall-Shockley-Read recombination in optimized samples.

Sub-micron GaInAs/InP hot electron transistors by EBL process and size dependence of current gain

Sub-micron hot electron transistors (HETs) fabricated by electron beam lithography (EBL) and the size dependence of current gain in HETs are described. The key process to fabricate small HETs is the small opening of the polyimide layer by dry-etching with bi-layer (PMMA/LS-SOG) resist. In this etching, removal of scum by slight wet etching and release of stress are essential to make a small opening (160×350 nm 2). The smallest emitter size of fabricated HET was (0.3×1.5+0.6×1) μm 2 and a Gummel plot with a current gain of 4 was observed. This gain was almost the same as that of large HETs (20×50 μm 2). In comparison with previously fabricated small HETs with SiO 2 layer, small HETs with polyimide layer show higher current gain.

Low loss static induction devices (transistors and thyristors)

To decrease the power loss, a current gain of a bipolar mode Static Induction Transistor (BSIT) is examined with quasi-one-dimensional analysis. The current gain dependence on source contact area is presented with experimental, analyzed and simulated results. Concerning Static Induction Thyristor (SIThy), the switching speed improvement methods are presented to reduce the switching loss of device. A proton irradiation, or a shorting method is a useful technique to decrease the switching time and switching loss of SIThy.

Non-equilibrium carrier transport in the base of heterojunction bipolar transistors

The conventional drift-diffusion equation is inadequate to analyze ballistic effects. In most device analysis, thermoelectric effects associated with gradients in the carrier temperature are assumed to be small. The base thickness dependence of current gain as a result of non-equilibrium transport of electrons in the base was experimentally shown by many researchers. We present a simulation to analyze the electron transport in the base region of an HBT based on the carrier density balance, momentum balance, and energy balance equations. Transistors with base thickness of 1000 Å and 2500 Å are investigated. Simulation results of electron transport in the base region indicates that tunneling electrons give rise to unique transport characteristics in the base of HBTs. The density profile is found as a result of transition from ballistic to diffusive transport in the base region. The range of observed non-equilibrium transport and the carrier density and temperature profiles in the base region are functions of average momentum and energy relaxation times. The non-equilibrium effects are shown to exist up to 1000 Å in the base region of HBTs. The simulation results are in good agreement with experimental data.

An analytical model for determining carrier transport mechanism of polysilicon emitter bipolar transistors

An analytical model is proposed by including carrier transport mechanisms which previous unified analytical models do not consider: minority carrier combination at both sides of polysilicon-silicon interfacial oxides and thermionic emission over segregation potential barriers for determining the precise carrier transport mechanisms which govern current gain and specific emitter interfacial resistivity. This approach allows us to gain an insight into carrier transport mechanisms and provides a distinct image for polysilicon emitter bipolar devices. With the consideration of the interfacial capture cross section as a function of temperature, the dependence of current gain for devices given an HF etch prior to polysilicon deposition on temperature is first explained successfully. For improving device performance, some directive suggestions are presented. >

Theoretical analysis of current gain of normally-off junction type field-effect transistor

In this study, the channel potential distribution and the current gain of normally-off junction-type field effect transistors were calculated with a simplified model and are reported here. Furthermore, the theoretical temperature dependence, drain-current dependence and dependence of current gain on channel dimensions have been compared with published experimental results and there is good agreement.

Growth of high quality AlGaAs/GaAs heterostructures by molecular beam epitaxy for photonic and electronic device applications

Epitaxial growth of smooth and high purity Al x Ga 1− x As layer is fundamentally more difficult than that of GaAs because of complex growth kinetics, small surface migration rate of Al, high reactivity of Al with residual oxygen and other impurities in the growth system, and surface segregation of impurities in AlGaAs. In this article, these issues are briefly reviewed and methods are suggested to improve the bulk and interfacial properties of AlGaAs/ GaAs heterostructures. Ambient oxygen, if present, in AlGaAs affects both the bulk and the interfacial properties of the AlGaAs/GaAs heterostructures. As well as forming non-radiative recombination centers in GaAs and AlGaAs, O tends to accumulate at the GaAs/AlGaAs inverted (GaAs on AlGaAs) heterointerfaces even when GaAs is just one monolayer thick. Furthermore, the Si doping suppresses and Be doping favors incorporation of O in AlGaAs without any contribution from the Be source itself. Incorporation of O and other impurities reduces, and the quality of AlGaAs/GaAs heterointerfaces improves if the (100) GaAs substrates are misoriented towards 〈111〉A. On the off-axis substrates, we have observed a marked improvement in the performance of GaAs and InGaAs strained quantum well edge emitting lasers, and heterojunction bipolar transistors (HBTs). In HBTs, there is a significant reduction in current and geometry dependence of current gain, and a detailed analysis revealed a reduction in surface, space charge and bulk recombination components of base current.