Collector Doping Concentration Research Articles

Simulation Study of Overcurrent Turn-off Capability in 4500V IGBT

According to the requirement of IGBT's over-current turn-off capability, this paper analyzes the factors affecting the dynamic latch-up of IGBT chip during the over-current turn-off process, including the gate width of IGBT cell, the doping concentration of back P + collector and the dVce/dt when the IGBT is turned off. The simulation results show that the anti-dynamic latch-up capability of IGBT can be effectively improved by decreasing the gate width and back P + collector doping concentration. Through multi-cell parallel simulation, it is found that current concentration exists in the process of overcurrent trun-off, which leads to the further increase of the lattice temperature, and the overcurrent turn-off capability declines.

Influence of base carrier lifetime on the characteristics of 4H-SiC BJTs

The optimum range of the base electron lifetime (τnB0) in silicon carbide (SiC) bipolar junction transistors (BJTs) is qualitatively investigated in this paper, considering both the static and dynamic performance. The TCAD simulation results show that there is tradeoff between the current gain (β) and the turn-off time (tF). With τnB0 increasing, both β and tF increase. However, with a fixed base width, the base transport factor tends toward saturation when τnB0 exceeds certain value. Thus, the eclectic values of base electron lifetime with different base thickness are obtained. The influence of the base drive current is also discussed. According to the charge control theory, the excessive storage charge caused by overdrive has a great influence on turn-off delay time (tD). To solve this, a suitable base drive current is necessary. For the common 4H-SiC BJT structure, appropriate base drive under variable base and collector doping concentration is suggested.

A novel high performance TFS SJ IGBT with a buried oxide layer

A novel high performance trench field stop (TFS) superjunction (SJ) insulated gate bipolar transistor (IGBT) with a buried oxide (BO) layer is proposed in this paper. The BO layer inserted between the P-base and the SJ drift region acts as a barrier layer for the hole-carrier in the drift region. Therefore, conduction modulation in the emitter side of the SJ drift region is enhanced significantly and the carrier distribution in the drift region is optimized for the proposed structure. As a result, compared with the conventional TFS SJ IGBT (Conv-SJ), the proposed BO-SJ IGBT structure possesses a drastically reduced on-state voltage drop (Vce(on)) and an improved tradeoff between Vce(on) and turn-off loss (Eoff), with no breakdown voltage (BV) degraded. The results show that with the spacing between the gate and the BO layer Wo = 0.2 μm, the thickness of the BO layer Lo = 0.2 μm, the thickness of the drift region Ld = 90 μm, the half width and doping concentration of the N- and P-pillars Wn = Wp = 2.5 μm and Nn = Np = 3 × 10 cm−3, the Vce(on) and Eoff of the proposed structure are 1.08 V and 2.81 mJ/cm2 with the collector doping concentration Nc = 1 × 1018 cm−3 and 1.12 V and 1.73 mJ/cm2 with Nc = 5 × 1017 cm−3, respectively. However, with the same device parameters, the Vce(on) and Eoff for the Conv-SJ are 1.81 V and 2.88 mJ/cm2 with Nc = 1 × 1018 cm−3 and 1.98 V and 2.82 mJ/cm2 with Nc = 5 × 10 cm−3, respectively. Meanwhile, the BV of the proposed structure and Conv-SJ are 1414 V and 1413 V, respectively.

Analytical base-collector depletion capacitance in vertical SiGe heterojunction bipolar transistors fabricated on CMOS-compatible silicon on insulator

The base—collector depletion capacitance for vertical SiGe npn heterojunction bipolar transistors (HBTs) on silicon on insulator (SOI) is split into vertical and lateral parts. This paper proposes a novel analytical depletion capacitance model of this structure for the first time. A large discrepancy is predicted when the present model is compared with the conventional depletion model, and it is shown that the capacitance decreases with the increase of the reverse collector—base bias—and shows a kink as the reverse collector—base bias reaches the effective vertical punch-through voltage while the voltage differs with the collector doping concentrations, which is consistent with measurement results. The model can be employed for a fast evaluation of the depletion capacitance of an SOI SiGe HBT and has useful applications on the design and simulation of high performance SiGe circuits and devices.

A Base-Emitter Self-Aligned Multi-Finger Si1−xGex/SiPower Heterojunction Bipolar Transistor

With a crystal orientation dependent on the etch rate of Si inKOH-based solution, a base-emitter self-aligned large-area multi-fingerconfiguration power SiGe heterojunction bipolar transistor (HBT) device(with an emitter area of about 880 μm2) is fabricated with2 μm double-mesa technology. The maximum dc current gain is 226.1. Thecollector–emitter junction breakdown voltage BVCEO is 10 Vand the collector-base junction breakdown voltage BVCBO is16 V with collector doping concentration of 1×1017 cm−3and thickness of 400 nm. The device exhibited a maximum oscillationfrequency fmax of 35.5 GHz and a cut-off frequency fT of24.9 GHz at a dc bias point of IC = 70 mA andthe voltage between collector and emitter is VCE = 3 V. Loadpull measurements in class-A operation of the SiGe HBT are performed at1.9 GHz with input power ranging from 0 dBm to 21 dBm. A maximum outputpower of 29.9 dBm (about 977 mW) is obtained at an input power of 18.5 dBmwith a gain of 11.47 dB. Compared to a non-self-aligned SiGe HBT withthe same heterostructure and process, fmax andfT are improved by about 83.9% and 38.3%, respectively.

Model of transit time for SiGe HBT collector junction depletion-layer

The transit time through collector junction depletion-layer is an important parameter that influences AC gain and frequency performance. In SiGe heterojunction bipolar transistor (HBT) collector junction, the depletion-layer width is given in three cases. The models of collector depletion-layer transit time, considering the collector current densities and base extension effect, are established and simulated using MATLAB. The influence of the different collector junction bias voltage, collector concentration of As or P dopant and collector width on collector junction transit time is quantitatively studied. When the collector junction bias voltage, collector doping concentration and collector width are large, the transit time is quite long. And, from the results of simulations, the influence of the collector depletion-layer transit time on frequency performance is considerable in SiGe HBT with a thin base, so it could not be ignored.

NUMERICAL INVESTIGATION OF THE EFFECT OF DOPING PROFILES ON THE HIGH FREQUENCY PERFORMANCE OF InP/InGaAs SUPER SCALED HBTs

Our simulations show that the emitter and collector doping profile engineering is very important for the transistor optimization, in particular, adjusting the low doped emitter section to the depletion length resulted in the decrease of the emitter series resistance and increased ft and fmax; decreasing of the collector doping concentration and shrinking the collector thickness reduced the collector transit time. Accounting for the lateral diffusion of hot electrons in the device with submicron emitter was found to be important in the transistor optimization process. This effect determines the effective thickness of the emitter finger and the value of the push-out current.

Non-selective growth of SiGe heterojunction bipolar transistor layers at 700C with dual control of n and p type dopant profiles

This paper describes the growth of the collector, base, and emitter layers of a SiGe HBT in a single epitaxy process. A non-selective SiGe heterojunction bipolar transistor growth process at 700 °C has been developed, which combines n-type doping for the Si collector, p-type doping for the SiGe base and n-type doping for the Si emitter cap. Control of the collector doping concentration by varying the growth conditions is shown. The boron tailing edge from the SiGe base into the Si emitter layer was removed by interrupting the growth process with a hydrogen flow after the SiGe base growth but before the Si emitter growth to remove the dopant gas from the chamber. The layer thicknesses are compared using three different analytical techniques–secondary ion mass spectroscopy (SIMS), transmission electron microscopy (TEM), and spectroellipsometry. A good agreement was obtained for the three different methods.

A high-power and high-gain X-band Si/SiGe/Si heterojunction bipolar transistor

A double mesa-type Si/SiGe/Si (n-p-n) heterojunction bipolar transistor (HBT) with record output power and power gain at X-band (8.4 GHz) is demonstrated. The device exhibits collector breakdown voltage BV/sub CBO/ of more than 24 V and a maximum oscillation frequency f/sub max/ of 37 GHz. Under continuous-wave operation and class-AB biasing conditions, 24.2-dBm (263-mW) RF output power with concurrent gain of 6.9 dB is measured at the peak power-added efficiency (28.1%) from a single ten-emitter fingers (780-/spl mu/m/sup 2/ emitter area) common-base HBT. The maximum RF output power achieved is as high as 26.3 dBm (430 mW in saturation) and the maximum collector efficiency is 36.9%. The low collector doping concentration together with the device layout result in negligible thermal effects across the transistor and greatly simplifies the large-signal modeling. The conventional Gummel-Poon model yields good agreement between the modeled and the measured de characteristics and small-signal S-parameters. The accuracy of the model is further validated with the measured power performance of the SiGe power HBT at X-band. These results set a benchmark for power performance for SiGe-based HBTs and indicate promise for their implementation in efficient X-band power-amplifier circuits.

Physical compact collector-emitter breakdown model for heterojunction bipolar transistors

Collector-emitter breakdown in npn HBTs is modeled using a base-collector current equal to I h = α i I c, where I c is the collector current and α i is the integral of the electron impact ionization coefficients over the base-collector depletion depth. We fit the α integrals for collector doping concentrations N d ∼ 0.08 to 1 × 10 17 cm −3 to functions of the collector voltage. The model is suitable for SPICE and harmonic balance simulators, is temperature dependent, and allows voltages to be swept above the collector-emitter breakdown limit without catastrophic effects to the model convergence.

Optimization of AlGaAs/GaAs heterojunction bipolar transistors for current gain, cutoff frequency and maximum frequency

The intrinsic HBT configurations (e.g. doping concentrations and layer thicknesses) are optimized for the current gain, cutoff frequency, and maximum oscillation frequency. The optimization is carried out based on an analytical HBT model which includes the high-current and thermal effects. The effects of the emitter, base and collector doping concentrations and layer thicknesses on the HBT performance are calculated and discussed. Optimal HBT intrinsic configurations, together with the corresponding HBT performance, are also suggested for both high-current and low-current regions.

Transit time of fast bipolar transistors at high collector-current densities

This paper presents a physical description (not an empirical expression) of the forward transit time τ f in fast bipolar transistors at high collector-current densities by using only physical parameters. The transition between the regimes of the weak and strong increase in τ f is defined and physically described with the aid of the critical collector-current density j CC redefined in this paper. Furthermore, the slopes of τ f vs j C for both regimes are expressed analytically as functions only of physical parameters such as technological data (e.g. widths of the base w B and collector w C , collector doping concentration N C , etc.) as well as operating conditions (base-collector voltage V BC and temperature T). A highly-accurate analytical formula derived strictly from physical principles is given for a 1-D description of the forward-transit time τ f for a large range of collector-current density. The accuracy of the physical model is checked and verified with results obtained from device simulations and measurements on fast self-aligned Si n- p- n bipolar transistors for various technological data and temperatures.

Hot-carrier-induced photovoltage in silicon bipolar junction transistors

As bipolar junction transistors (BJTs) are scaled down, the current density increases and base pushout may happen. To prevent base widening, the collector doping concentration is increased; therefore, this increases the electric field in the base-collector junction. In the active operation of BJTs, impact ionization happens and impact-ionization-induced photon emission is created in the base-collector (BC) junction and photon absorption happens in the base-emitter (BE) junction. This makes the carrier injection from the BE junction to the BC junction with avalanche different from that without avalanche. Similarly, the avalanche-induced light emission in the BE junction will induce photocarriers in the BC junction diode. In this paper, we report observation of the photovoltage in the BC junction resulting from hot-carrier electroluminence in the BE junction on a conventional low-power n- p- n bipolar transistor. We found a photovoltage of 0.36 V and a collector current reversal in the inverse active operation.

Design for optimal values Design for optimal values of parameters of epitaxial bipolar power transistor switches

This paper deals with the design of epitaxial bipolar power transistor switches. An optimization procedure is developed that completely specified the parameters of the device with only two input data required—the collector-emitter sustaining voltage and the forced current gain. Theoretical equations for optimized collector doping concentrations, epitaxial layer thckness and the maximum collector current controllable at the limit of hard-saturation are derived. The optimization procedure is concise and involves little computational effort to determine the transistor parameters.

Low-temperature avalanche multiplication in the collector-base junction of advanced n-p-n transistors

The collector-base junction avalanche in advanced n-p-n transistors in the temperature range of 293 to 83 K is described. The multiplication factor is shown to increase exponentially with decreasing temperature. The dependence decreases with increased collector doping concentration and, for the same device, with increased reverse bias. At a fixed collector bias, it is roughly constant at low current density, but varies with I/sub c/ at high-level injection due to space-charge modulation. Measurements at low temperatures excluded self-heating in the devices, and it was possible to study high-level injection effects at collector current densities higher than 10 mA/ mu m/sup 2/. Extensive computer simulations were performed to study the effects of the field and carrier distributions. It was observed that, at very high current densities, when the injected carrier density in the collector junction exceeds 1*10/sup 17/ cm/sup -3/, there is an anomalous drop in the avalanche multiplication rate that conventional device simulators fail to predict. The latter is attributed to electron-electron scattering that retards impact ionization by quickly redistributing the excess energy through interparticle collisions. >

Breakdown behavior of GaAs/AlGaAs HBTs

Avalanche breakdown behavior at the collector junction of the GaAs/AlGaAs HBT (heterojunction bipolar transistor) has been studied. Junction breakdown characteristics displaying hard breakdown, soft breakdown, and negative resistance breakdown behavior were observed and are interpreted by analysis of localized microplasma effects, uniform microplasma-free behavior, and associated current gain measurements. Light emission from the collector-base junction of the GaAs/AlGaAs HBT was observed and used to investigate breakdown uniformity. Using a simple punchthrough breakdown model, the theoretical breakdown curves at different collector doping concentrations and thicknesses were computed and found to be in agreement with maximum breakdown voltages measured from devices displaying the most uniform junction breakdown. The serious current gain degradation of GaAs/AlGaAs HBTs at low current densities was analyzed in connection with the measurement of a large collector-emitter breakdown voltage. The unexpected functional relationship between the collector-emitter breakdown voltage and collector-base breakdown voltage is explained by the absence of a hole-feedback effect for devices not exhibiting transistor action.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Evaluation of epitaxial planar transistors based on their double diffused impurity profile distribution

A simple procedure is described for the evaluation of large geometry, low frequency and small geometry, high frequency type epitaxial planar transistors in terms of the impurity profile parameters based on their double-diffused impurity profile distribution. The profile parameters: collector doping, base and emitter surface concentrations, emitter and collector junction depths and collector thickness have been obtained from the measurement of the capacitance C( V) of emitter and collector junction, I–V characteristic of emitter-base junction, collector junction breakdown voltage and diffused emitter and base window areas. Making use of the calculated impurity profile distribution the parameters: emitter capacitance and saturation time constant have been calculated for several transistors having f T in the range 300–700 MHz and compared with the corresponding measured values and close agreement has been obtained. Fairly good agreement has also been obtained in calculated and measured junction depths.

Bipolar transistor structure to exhibit a negative resistance region†

Abstract A bipolar transistor structure is considered with base and collector doping concentrations such that significant space charge modulation can occur at high current densities. A theoretical analysis indicates the possibility of two distinct negative resistance regions. Some experimental work is presented in support of the theoretical predictions.