Base Collector Research Articles

Control of radiative base recombination in the quantum cascade light-emitting transistor using quantum state overlap

The concept of the quantum cascade light-emitting transistor (QCLET) is proposed by incorporating periodic stages of quantum wells and barriers in the completely depleted base–collector junction of a heterojunction bipolar transistor. The radiative band-to-band base recombination in the QCLET is shown to be controllable using the base–collector voltage bias for a given emitter–base biasing condition. A self-consistent Schrodinger–Poisson Equation model is built to validate the idea of the QCLET. A GaAs-based QCLET is designed and fabricated. Control of radiative band-to-band base recombination is observed and characterized. By changing the voltage across the quantum cascade region in the QCLET, the alignment of quantum states in the cascade region creates a tunable barrier for electrons that allows or suppresses emitter-injected electron flow from the p-type base through the quantum cascade region into the collector. The field-dependent electron barrier in the base–collector junction manipulates the effective minority carrier lifetime in the base and controls the radiative base recombination process. Under different quantum cascade region biasing conditions, the radiative base recombination is measured and analyzed.

Tunneling Modulation of Transistor Lasers: Theory and Experiment

The coherent photons generated at the base quantum wells in the transistor laser (TL) interact with the collector field and “assist” electron tunneling from the valence band of the base to the conduction band states of the collector. The cavity coherent photon intensity effect on photon-assisted tunneling in the TL has resulted in the realization of a novel photon-field enhanced optical absorption. This intra-cavity photon-assisted tunneling (ICPAT) in the TL or the light-emitting transistor is the unique property of voltage (field) modulation and the basis for ultrahigh speed direct tunneling photon modulation and switching. In addition, a new tunneling current modulation gain in a “new form” of transistor is discovered based on the collector tunneling holes feedback to the base and dielectric relaxation base transport. The TL, owing to its unique three-terminal configuration and the complementary nature of its optical and electrical collector output signals, enables fast base recombination, collector tunneling, and OEO feedback, which has resulted in the realization of compact electro-optical applications, such as non-linear signal-mixing, frequency multiplication, OE tunneling transistor, and electrical and optical bistability.

Highly Efficient 5.15- to 5.85-GHz Neutralized HBT Power Amplifier for LTE Applications

A highly efficient fully integrated 5.15- to 5.85-GHz GaAs HBT differential power amplifier (PA) is implemented for long-term evolution (LTE) handset applications considering LTE licensed-assisted access. A simple and practical output network, based on an on-chip transformer, is proposed to achieve low loss. A neutralization technique to mitigate the parasitic base–collector capacitance is also adopted to improve PA performances. The implemented PA achieved a high gain of 26.6–28.1 dB and saturated power of 30.5–31.1 dBm with a high peak power-added efficiency of 40.4%–44.5% under a continuous-wave signal test across 5.15–5.85 GHz. When tested with 20- and 40-MHz bandwidth quadrature phase-shift keying LTE signals, the PA showed an adjacent channel leakage ratio of −33 dBc up to output powers of 24.1–24.4 and 22.2–22.8 dBm, respectively.

Graphene–Silicon-Based High-Sensitivity and Broadband Phototransistor

Graphene–silicon vertical junction is utilized here for fabrication of high-responsivity and broadband phototransistor. Graphene–silicon as a Schottky junction plays the role of collector–base junction in a bipolar junction phototransistor. We propose graphene–silicon-based phototransistor as a promising candidate for fabrication of high-gain photodetector with responsivity as high as 11 A/W. Gain and ON/OFF ratio of our fabricated device reach up to 18 and 100, respectively. Our results show that the graphene–silicon-based phototransistor is sensitive to a broad range of incident light from visible to IR spectrum. Our results open up a way to fabricate highly sensitive photodetectors suitable for silicon integrated electronics.

Effect of quantum well position on the distortion characteristics of transistor laser

The effect of quantum well position on the modulation and distortion characteristics of a 1300 nm transistor laser is analyzed in this paper. Standard three level rate equations are numerically solved to study this characteristics. Modulation depth, second order harmonic and third order intermodulation distortion of the transistor laser are evaluated for different quantum well positions for a 900 MHz RF signal modulation. From the DC analysis, it is observed that optical power is maximum, when the quantum well is positioned near base–emitter interface. The threshold current of the device is found to increase with increasing the distance between the quantum well and the base–emitter junction. A maximum modulation depth of 0.81 is predicted, when the quantum well is placed at 10 nm from the base–emitter junction, under RF modulation. The magnitude of harmonic and intermodulation distortion are found to decrease with increasing current and with an increase in quantum well distance from the emitter base junction. A minimum second harmonic distortion magnitude of −25.96 dBc is predicted for quantum well position (230 nm) near to the base–collector interface for 900 MHz modulation frequency at a bias current of 20 Ibth. Similarly, a minimum third order intermodulation distortion of −38.2 dBc is obtained for the same position and similar biasing conditions.

An Intermediate Frequency Amplifier for High-Temperature Applications

This paper presents a two-stage small signal intermediate frequency amplifier for high-temperature communication systems. The proposed amplifier is implemented using in-house silicon carbide bipolar technology. Measurements show that the proposed amplifier can operate from room temperature up to 251 °C. At a center frequency of 54.6 MHz, the amplifier has a gain of 22 dB at room temperature, which decreases gradually to 16 dB at 251 °C. Throughout the measured temperature range, it achieves an input and output return loss of less than −7 and −11 dB, respectively. The amplifier has a 1-dB output compression point of about 1.4 dBm, which remains fairly constant with temperature. Each amplifier stage is biased with a collector current of 10 mA and a base–collector voltage of 3 V. Under the aforementioned biasing, the maximum power dissipation of the amplifier is 221 mW.

Room temperature operation of electro-optical bistability in the edge-emitting tunneling-collector transistor laser

Optical bistable devices are fundamental to digital photonics as building blocks of switches, logic gates, and memories in future computer systems. Here, we demonstrate both optical and electrical bistability and capability for switching in a single transistor operated at room temperature. The electro-optical hysteresis is explained by the interaction of electron-hole (e-h) generation and recombination dynamics with the cavity photon modulation in different switching paths. The switch-UP and switch-DOWN threshold voltages are determined by the rate difference of photon generation at the base quantum-well and the photon absorption via intra-cavity photon-assisted tunneling controlled by the collector voltage. Thus, the transistor laser electro-optical bistable switching is programmable with base current and collector voltage, and the basis for high speed optical logic processors.

96 GHz 4.7 mW low‐power frequency tripler with 0.5 V supply voltage

Using forward-biased base–collector voltage (VBC) in high-speed circuits is usually not attractive due to the performance degradation compared with biasing heterojunction bipolar transistors (HBTs) in the forward-active region. However, the use of ultra-low supply voltage in millimetre-wave circuits provides an interesting application scenario not only for demonstrating the potential of modern silicon germanium (SiGe) HBT technologies in implementing severely power-constrained wireless circuits on silicon but also for verifying the accuracy of compact models beyond standard characteristics typically measured by foundries. The results of a 96 GHz frequency tripler deliberately designed with a reduced supply voltage (0.5 V) in a 130 nm SiGe HBT technology are presented. With only 4.7 mW DC power consumption, this frequency tripler achieves a conversion loss of 3.8 dB, generating a 96 GHz output signal with only −10 dBm input signal at 32 GHz. The impact of transistor series resistances on the tripler performance is also analysed.

A Closed-Form Solution for the Low-Current Collector Transit Time in Group IV and Group III-V HBTs

In certain types of heterojunction bipolar transistors (HBTs), the carrier transit time associated with the base-collector (BC) space-charge region constitutes a significant contribution to the total transit time. In many compact models, the low-current BC transit time is lumped in with the total low-current transit time and often assumed to be constant—dependent only on the collector width and material saturation velocity. This assumption, however, is insufficient for modeling high-voltage Si-based HBTs as well as for III-V HBTs, where the negative differential mobility (NDM) effect can become relevant in high-speed low-power circuits. This paper presents a closed-form solution for the low-current collector transit time based on a novel accurate analytical velocity-field formulation, covering both group IV and group III-V semiconductor materials. The new solution includes the NDM effect and is suitable for implementation in compact models, and its relevance and accuracy are demonstrated for both TCAD simulated and measured data.

Impact of Breakdown Voltage on Gamma Irradiation Effects in 0.13- $\mu \text{m}$ and 0.25- $\mu \text{m}$ SiGe HBTs

We have investigated the ionization damage by 60Co gamma irradiation in 0.13- and 0.25- $\mu \text{m}$ SiGe heterojunction bipolar transistors (HBTs). Both technologies feature high-speed HBTs (HS-HBTs) together with high-voltage HBTs (HV-HBTs). Base current degradation with increasing total irradiation dose is studied. An identical behavior of corresponding HS-HBT and HV-HBT is found for operation in forward mode probing the emitter–base junction. In reverse mode where the collector base junction is determining the base current degradation, HV devices exhibit larger degradation than their HS counterparts. The increased width of the collector–base space charge region in HV devices leads to enhanced interface recombination at the adjacent Si/oxide interfaces and stronger base current degradation. TCAD simulations of device degradation suggest a linear relationship between total irradiation dose and radiation-induced interface state density $N_{\mathrm{ it}}$ .

Numerical evaluation of a solar chimney geometry for different ground temperatures by means of constructal design

The present work aims to numerically study the influence of geometric parameters over the available power of solar chimney power plant (SCPP) by means of Constructal Design. The influence of different imposed ground temperatures (mimicking the effect of different solar incidence on collector device) over the optimal shapes is also evaluated. The geometry is submitted to three constraints: collector, turbine and chimney areas. Moreover, three degrees of freedom are taken into account: R/H (ratio between collector radius and its inlet height), R1/H2 (ratio between the radius and height of chimney) and H1/H (ratio between the height of collector base and collector inlet height) which is constant (H1/H = 10.0). The mixed convective flow is incompressible, turbulent, steady, in two-dimensional axisymmetric domain. Time-averaged conservation equations of mass, momentum and energy (RANS) are numerically solved using the finite volume method (FVM). For closure modeling of turbulence it is employed the standard k – ε model. Results showed a strong influence of the chimney and collector geometry over the available power. Moreover, geometric parameters of collector and chimney must be evaluated in a combined way. It was also noticed a large sensibility of the ground temperature over the available power and geometric effects.

Comparison of 1 MeV electron, Co-60 gamma and 1 MeV proton irradiation effects on silicon NPN transistors

ABSTRACTThe total dose effects of 1 MeV electrons on the dc electrical characteristics of silicon NPN transistors are investigated in the dose range from 100 krad to 100 Mrad. The different electrical characteristics such as Gummel characteristics, excess base current (ΔIB), dc current gain (hFE), transconductance (gm), displacement damage factor (K) and output characteristics were studied in situ as a function of total dose. A considerable increase in base current (IB) and a decrease in hFE, gm and ICSat was observed after 1 MeV electron irradiation. The collector–base (C–B) junction capacitance of transistors was measured to estimate the change in the effective carrier concentration. After 1 MeV electron irradiation, a considerable degradation in capacitance was observed. The plot of (1/C2) versus voltage shows that the effective carrier concentration and built-in voltage (Vbi) increase marginally upon 1 MeV electron irradiation. The results of 1 MeV electron irradiation were compared with 1 MeV proton and Co-60 gamma irradiation results in the same dose range. The degradation for 1 MeV electron and Co-60 gamma-irradiated transistors was significantly less when compared to 1 MeV proton-irradiated transistor. The 1 MeV proton, 1 MeV electron and Co-60 gamma-irradiated transistors were subjected to isochronal annealing to analyze the recovery of the electrical parameters.

Thermal performance evaluation of alumina-water nanofluid in an inclined direct absorption solar collector (IDASC) using numerical method

Abstract In this paper, thermal performance of a nanofluid in an inclined direct absorption solar collector (IDASC) is evaluated using a hybrid of finite difference method (FDM) and Differential Transformation Method (DTM) called Hybrid FDM-DTM. After presenting the governing equations and solving by hybrid method, the accuracy of results is examined by fourth order Runge-kutta numerical method. Alumina/water nanofluid is considered as the working fluid in the collector and two boundary conditions are defined for the collector base; a constant temperature and convection heat transfer. The second condition leads to insulated base when the coefficient is assumed to be zero. For both boundary conditions, the problem is analyzed and collector efficiency is calculated. Results confirm that to reach an efficient collector, nanoparticles volume fraction, convection coefficient and base temperature should be considered in maximum possible values.

An Approach for Estimation of Cathode Voltage Drop in an Aluminum Reduction Cell with an Inclined Carbon Block and a Copper Insert

Numerical models of a cathode block assembly in a Hall–Heroult cell, comprising of liquid aluminium, carbon block, current collector, ramming paste and a copper insert were built and the finite element method simulations were carried out to model the cathode voltage drop (CVD), the current distribution and, the effect of geometrical parameters on the CVD. The objective of the study was to quantify the drop in the CVD for different cathode assembly design. Flat- and inclined-interface carbon block top-surface and a copper insert versus the conventional insert-free designs were simulated with a myriad of other geometrical parameters to optimise the design. The results informed about the optimum insert positioning to about 75 mm from the collector base and the energy saving possibilities due to reduction in the CVD with a cathode design with inclined-interface carbon block and copper insert in the collector bar.

Experimental study of bias dependence of pulsed laser-induced single-event transient in SiGe HBT

This work presents a comprehensive investigation of single-event transient (SET) in SiGe HBT induced by pulsed laser irradiation at different bias conditions. The impacts of collector voltage VCC and base voltage VB on SET are compared and discussed. Experimental results show that SET in SiGe HBT highly depends on the applied bias conditions during irradiation. The underlying physical mechanisms are analyzed in detail. It is found that the variation of collector transient current approximately satisfies an ideal exponential discharge law. The additional discharge path plays a significant role in collector charge collection and discharge time constant once the transistors arrive at the reverse-active mode.

Switching Mechanisms Triggered by a Collector Voltage Ramp in Avalanche Transistors With Short-Connected Base and Emitter

Although Marx-bank connection of avalanche transistors is widely used in applications requiring high-voltage nanosecond and subnanosecond pulses, the physical mechanisms responsible for the voltage-ramp-initiated switching of a single transistor in the Marx chain remain unclear. It is shown here by detailed comparison of experiments with physical modeling that picosecond switching determined by double avalanche injection in the collector–base diode gives way to formation and shrinkage of the collector field domain typical of avalanche transistors under the second breakdown. The latter regime, characterized by a lower residual voltage, becomes possible despite a short-connected emitter and base, thanks to the 2-D effects.

A Pseudobipolar Junction Transistor for a Sensitive Optical Detection of Biomolecules

A new optical sensor system, called the pseudo-bipolar junction transistor (BJT) optical measurement system (PBOS), based on a pseudo-BVceo of the BJT is proposed by adding a back-to-back connection of a laser diode (LD) (or an LED) and a p-i-n photodiode (PD) in the conventional optical measurement system operated in the photoconductive mode. A back-to-back connection of two optoelectronic devices and illumination of the light from the LD to the PD generates an optical current gain in the PD. It is similar to the current flowing mechanism in the BJT under the base open condition, in which the forward emitter–base junction current generates an electrical current gain in the base–collector junction. Similar to the negative differential resistance (NDR) after BVceo of the BJT, the NDR is observed in the PBOS. Operating the PBOS in the NDR region, the system can provide much higher sensitivity and lower limit of detection compared with the conventional optical measurement system in the photoconductive mode with a p-i-n PD. We show a mathematical model of the sensitivity of the PBOS to the transmittance of the optical path and our initial data for glucose detection as a potential application of the system.

SWOT ANALYSIS OF SAINSBURY’S SUPERMARKET

Sainsbury’s is the second largest supermarket chain in the UK after Tesco. However, Sainsbury’s has been losing market share to its competitors, the biggest grocery retailer, Tesco and ASDA, the US retailer, which has a market share of 17% now. Hence, in order to increase its market share, Sainsbury’s made a new strategic step by joining Nectar Loyalty Program. The Nectar loyalty program is a crucial part of the strategy of Sainsbury’s. The retailer was convinced that a strong and attention-getting new rewards program could help in improving current market position. The main advantages of using the Nectar Card were based on the ease of achieving rewards by collecting points into one combined account. After one year, Nectar’s collector base was already bigger than the collector base of its largest competitor, Tesco. In addition, based on the satisfaction survey, most of the Nectar’s collectors rated Nectar as better than other loyalty programs. Nectar offers Sainsbury’s detailed information about what their customers are doing day-to-day. Sainsbury’s can use this information to decide which stock to convey in which stores. The Nectar also helps Sainsbury’s in better and more efficient targeting of its customers. The Nectar program that is based on partnership among various sponsors has some advantages and some drawbacks compared to a single vendor loyalty program, like the program of Tesco. Sainsbury’s, as the most important sponsor, has profited from the participation in the program in customer lift, acquisition, retention and up-selling. Now, it is highest time for Sainsbury’s to decide, whether Nectar is the most suitable strategic approach to respond to recent changes in its market position Therefore, the problem statement originating from the case study is as follows: Should Sainsbury’s stay with the Nectar loyalty program in order to gain market share of 5% and increase average share of wallet of its customers by 10% in the upcoming 5 years?

An Improved Noise Model for SiGe HBT With an Inductive Breakdown Network in the Avalanche Region

In this paper, an improved radio-frequency (RF) noise model is extended for silicon germanium (SiGe) heterojunction bipolar transistors (HBTs) by applying RF avalanche delay mechanism to investigate noise performance in the breakdown region where reliability is a concern. The impact of inductive feedback due to base–collector (BC) junction avalanche breakdown on noise performance is analyzed and explained by utilizing this improved noise model incorporating an inductive network. The avalanche effects on noise sources are verified and explained physically by the dead-space theory. The contributions of electrons and holes to the avalanche noise are taken into account by including an electron- and hole-breakdown network in the presented noise model. The presented method is compared with the conventional approach. When the avalanche noise is absorbed by base and collector noise sources as in the conventional RF noise model without a breakdown network, simulated noise parameters deviate from experimental data at breakdown. Instead, good agreement between measured and simulated noise parameters and $S$ -parameters from the presented RF noise model is achieved in the inductive breakdown and active regions. The presented noise model and the obtained parameters can be applied to SiGe HBT circuits for reliability investigation.

Synergistic Effect of Ionization and Displacement Defects in NPN Transistors Induced by 40-MeV Si Ion Irradiation With Low Fluence

Based on 3DG110 transistors and special gated NPN (GNPN) transistors, the characteristic of the synergistic effect between ionization and displacement defects induced by 40-MeV silicon (Si) ions with low fluence was investigated in terms of deep-level transient spectroscopy (DLTS). Nonlinear relationship, produced by the synergistic effect, between low fluence and radiation response can be obviously observed in the bipolar junction transistors (BJTs) under the exposure of 40-MeV Si ions. The DLTS signals of displacement defect centers and oxide-trapped charges are detected in the base–collector junction of the 3DG110 transistors. Meanwhile, based on the GNPN transistors, the DLTS signals of interface traps and displacement defects are measured in the base–collector junction. By comparison of the change in electrical parameters and the DLTS signals, it is found that the interface traps induce an enhanced effect to displacement defects in the base–collector junction of NPN BJT, whereas the oxide-trapped charge can suppress the DLTS signals of deep-level centers to a certain extent. Compared with the suppression action, the enhanced effect rising from ionization damage gives more contribution to the displacement damage. Moreover, the bias used during DLTS measurements can influence the characteristics of DLTS signals caused by oxide-trapped charge and interface traps. With increasing bias, both the height and temperature of ionization defect peaks in the DLTS spectra will increase, illustrating that concentration and energy level of these defects are raised.