Collector Doping Profile Research Articles

Experimental and Theoretical Investigation of Collector Spacer and Doping Profile on Triple‐Barrier Resonant Tunneling Diodes

Upcoming THz applications require compact, robust, and efficient sources with high output‐power. Among electronic devices, resonant tunneling diodes are a promising candidate for THz operation. Triple‐barrier resonant tunneling diodes provide a high degree of design and operation freedom. Zero‐bias detection and THz emission are possible with the same device due to the asymmetric structure and IV curve. However, more investigations in the layer stack design are required. An investigation is presented into the effect of collector spacer thickness and doping profile in the subcollector contact region. The aim is to simultaneously optimize the RF output‐power and cut‐off frequency in triple‐barrier structures. A series of devices with different collector spacers and two distinct doping profiles are fabricated. A trade‐off between collector spacer thickness and doping profile for either higher output power or cut‐off frequency is observed. In addition, the simulation results are presented from a nonequilibrium Green's function solver implemented in Python. Herein, a need for accurate determination of the extent of the nonequilibrium region to achieve simulation results matching the IV measurements is observed.

The Effect of Collector Region Design on Large-Signal Performance of Horizontal Current Bipolar Transistor (HCBT)

The impact of collector region design on large-signal performance of horizontal current bipolar transistor (HCBT) technology is investigated by calibrated time-domain load-pull measurements. Three representative high-performance devices of the same geometry but with different collector doping profiles, namely, uniform, n-well, and low-doped, are subjected to large-signal measurements wherein the radio frequency (RF) time-domain waveforms of current and voltage are measured to facilitate the determination of the maximum output power for each device. The extensive measurements outline the boundaries of the maximum collector current and voltage swings at RF determining linear operating area, which are a result of the physical phenomena in the high-current and high-voltage regimes, namely, the Kirk effect and impact ionization, respectively. While the highest-doped n-well HCBT provides the highest output power of 25.3 dBm at 1-dB gain compression, and the lowest-doped HCBT enables a wideband match at the collector, the HCBT with a uniform doping profile provides a tradeoff between the output power and bandwidth of the output match. The results show the versatility of HCBT technology as an alternative to CMOS and/or sillicon–germanium (SiGe) large-signal RF circuits for the front-ends (FEs) in the sub-6 GHz wireless communications range.

A Compact Formulation for Avalanche Multiplication in SiGe HBTs at High Injection Levels

This paper presents a unified physical formulation for the avalanche effect in silicon-germanium heterojunction bipolar transistors (SiGe HBTs) at different injection levels. Based on an analytical description of the resulting electric-field distribution, a closed-form analytical expression for the multiplication factor is derived and has been implemented in the HICUM compact model. The model accuracy close to and beyond the common-emitter breakdown voltage BVCEO has been assessed over a wide temperature range in comparison to measurements of SiGe HBTs with different collector doping profiles and emitter geometries.

On the RF Power-Handling Capabilities of Forward- and Inverse-Mode SiGe HBT RF Switches Fabricated on Thick-Film SOI

The radio frequency (RF) power-handling capability of forward- and inverse-mode diode-connected SiGe HBT RF switches fabricated on SOI is investigated. Two types of n-p-n SiGe HBTs, each with a different collector doping profile, are used in the ON path of the RF switch. Measured results show that the inverse-mode switches outperform the forward-mode switches in both off-state insertion loss and power handling and compression characteristics. A framework for understanding the differences observed in the distortion performance of the forward- and inverse-mode SiGe HBT switches is developed.

Enhanced fT and linearity performance of InGaP/GaAs HBTs using a non-uniform doping collector

In this paper, the ac and power linearity characteristics of InGaP/GaAs heterojunction bipolar transistors (HBTs) with collector doping design have been presented. The collector design is to employ a thin high-doping layer inside the low-doping collector. The thickness, doping and location of the inserted layer are systematically studied with consideration of breakdown characteristics and the Kirk effect. The Kirk effect is relieved by redistributed electric fields in the non-uniform doping collector to extend the operational current and thus to increase the cutoff frequency (fT) and output power (Pout). The collector current at the onset of the Kirk effect is extended from 9.6 to 17.3 mA and fT is increased from 36 to 48 GHz for a device size of 4 × 12 × 2 µm2. The corresponding improvement in the saturation output power is 2.2 dB measured at 1.8 GHz. In addition, the impact of the collector doping profile on the base–collector capacitance (CBC) and thus the linearity is simulated, discussed and measured. For an HBT with a thin high-doping layer being inserted 4000 Å from the base–collector junction, the experimental result on output third-order intercept point (OIP3) demonstrates the significant improvement by as large as 10 dB at a frequency of 1.8 GHz.

Simulations of non-uniform, nonlinear collector doping profiles for SiGe HBTs

In this work, the authors examine the effects of the shape of the collector doping profile in current-generation SiGe npn heterojunction bipolar transistors. The n-type doping profile in the region between the p-type SiGe base and the heavily doped n-type subcollector is simulated by various analytic functions and included in one-dimensional computer simulations. The results are examined in terms of RF performance versus breakdown. It is determined that altering the shape of the profile as compared to a uniform profile enables an increase in performance only in certain doping regimes. At high-integrated collector dose (low breakdown), profiles with their dose concentrated nearer the collector–subcollector junction outperform those that have their dose more evenly spread throughout the collector region. However at low-integrated collector dose (high breakdown) this advantage disappears. In fact the trend actually reverses in some cases such that for high-breakdown devices a uniform collector profile may be preferred. The advantage in FT of one profile over another can be as much as 15 GHz at a given breakdown voltage.

Analysis of the Kirk Effect in Silicon-Based Bipolar Transistors With a Nonuniform Collector Profile

In this paper, the Kirk effect has been analyzed for silicon-based bipolar transistors (BJTs) with a nonuniform collector profile. We show that, for any arbitrary collector doping profile, the Kirk effect starts when the electron concentration equals the average doping concentration in the depletion region. We present a basic guideline for determining the collector current density at the onset of Kirk effect (J/sub K/) for any collector doping profile and simple expressions for J/sub K/ and the electrical field in the collector drift region for the case of a linearly graded collector drift region. These analytical expressions are verified with device simulations. The Kirk effect for this kind of transistor is substantially different from that presented previously for transistors having a uniform collector drift region. For example, the possibility of the onset of the Kirk effect in a partially depleted collector occurs, while in a uniform collector profile the effect can only occur in a fully depleted collector. Our expressions can be used to do approximate analytical calculations for optimizing future BJTs.

Determining GaInP/GaAs HBT Device Structure by DC Measurements on a Two-Emitter HBT Device and High Frequency Transit Time Measurements

A method to monitor the GaInP/GaAs HBT device structure including emitter ledge thickness is demonstrated in this paper. The base thickness and base doping density are obtained through base transit time and base sheet resistance measurements while the base transit time is measured through the cut-off frequency measurements at various bias points. A large size two-emitter HBT device is used to measure the ledge thickness. Emitter doping profile and collector doping profile are obtained by the large size HBT device through C-V measurements. An FATFET device formed by two emitters as drain and source terminals and the interconnect metal as the on-ledge Schottky gate between two emitters is used to measure the ledge thickness.

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.

High Linearity InGaP/GaAs Power HBTs by Collector Design

Improved power linearity of InGaP/GaAs heterojunction bipolar transistors (HBTs) with collector design is reported. The collector design is based on nonuniform collector doping profile which is to employ a thin high-doping layer (5/spl times/10/sup 17/ cm/sup -3//200 /spl Aring/) inside the collector (1/spl times/10/sup 16/ cm/sup -3//7000 /spl Aring/). The additional thin high-doping layer within the collector shows no obvious effects and impacts in dc characteristics and device fabrication if the layer was inserted close to the subcollector. For an HBT with a thin high-doping layer being inserted 4000 /spl Aring/ from the base-collector junction, the experimental result on third-order intermodulation demonstrates the significant reduction by as large as 9 dBc and improved IIP3 by 5 dB under input power of -10 dBm at frequency of 1.8 GHz.

Mixed mode circuit and device simulation of RF harmonic distortion for high-speed SiGe HBTs

Mixed mode circuit and device simulation has been used to investigate the linearity properties––harmonic distortion of high-speed low voltage SiGe heterojunction bipolar transistors (HBTs). The simulation test-circuit included the active device, modeled by finite element simulation, as well as passive elements in a SPICE circuit for DC-feed and AC-coupling of the RF-signal. Different Ge-profiles for reduced harmonic distortion have been investigated and compared to a conventional high-speed graded Ge-profile. To find an optimized Ge-profile for RF-applications other figure-of-merits, such as maximum cut-off frequency and minimum noise figure were also simulated. Using the same mixed mode simulation approach the design of the epitaxial collector doping profile for high breakdown voltage, high cut-off frequency and reduced harmonic distortion was investigated.

Ge-profile design for improved linearity of SiGe double HBTs

The influence of Ge-profile design on SiGe HBT linearity-harmonic distortion has been quantified using finite element physical device simulation. It was demonstrated that proper Ge-profile tailoring allows the linearity to be improved for both low- and high-current operation. High injection heterojunction barrier effects are shown to have a significant influence on the higher order harmonics. The influence of the Ge-profile design on linearity was found to be comparable to the influence from the epitaxial collector doping profile.

Implanted collector profile optimization in a SiGe HBT process

Optimization of implanted collector doping profiles for a high-speed, low-voltage SiGe HBT process has been investigated experimentally and by device simulations. A low-energy antimony implantation has been combined with a standard selectively implanted collector using phosphorous, to achieve improved control of the collector doping profile. The simulations indicate that the narrow n-type doping peak formed by the antimony implantation allows the cut-off frequency f T to be increased without degrading the collector emitter breakdown voltage BV CEO. The fabricated devices demonstrate a highest f T of 60 GHz. Depending on the collector profile BV CEO values between 1.5 and 2 V were obtained.

Design and analysis of heterojunction bipolar transferred electron devices

The design of the heterojunction bipolar transferred electron device (HBTED) is considered. MOCVD-grown AlGaAs/GaAs HBTEDs were fabricated and 60 GHz operation was confirmed by on-wafer measurements. Analysis of the device operation is aided by the use of Monte Carlo device simulations, equivalent circuit model simulations and two-dimensional (2-D) drift-diffusion model simulations and the simulation results are compared with measurements on the fabricated HBTEDs and HBTED test structures. The effects of the external base-collector region and current spreading in the collector region are investigated and the latter is found to be of great importance. Our simulations show that having an appropriately graded collector doping profile can compensate the current spreading and this hypothesis is supported by measurement results. Conclusions are drawn regarding the design of practical HBTEDs for mm-wave oscillator applications.

Reduction of UHF power transistor distortion with a nonuniform collector doping profile

The linearity of a class-A, bipolar UHF power transistor is investigated. The device is intended for transmission of signals with multiple (TV) channels. Mixing between the various channels must be suppressed, which makes linearity an important parameter. This paper presents a novel approach, where process technology is specifically optimized to minimize distortion. It is shown that particularly the nonlinear collector-base capacitance strongly affects the linearity of this type of device. With a modified collector-base doping profile, the capacitance is manipulated. A nonuniform profile is introduced that significantly reduces third-order intermodulation. The profile consists of an arsenic doped spike that is grown epitaxially into the (otherwise) lightly doped collector. This reduces the bias dependence of C/sub cb/ and improves the tradeoff between linearity and breakdown or ruggedness. The reduction in third-order intermodulation is demonstrated both experimentally and by mixed-level MDS/MAIDS simulations.

A better insight into the performance of silicon BJTs featuring highly nonuniform collector doping profiles

This paper investigates the effects of highly nonuniform collector doping profiles on the speed and breakdown performance of silicon bipolar transistors. Monte Carlo and drift diffusion simulation results point out that a thin highly doped layer adjacent to the base collector junction can improve the device cut off frequency without deteriorating significantly the maximum oscillation frequency and the breakdown voltage, provided the voltage drop across this layer is lower than an effective threshold of approximately 1.2 V. Guidelines are given for choosing the doping, position, and thickness of this layer.

On the design and fabrication of novel lateral bipolar transistor in a deep-submicron technology

The performance of a npn Lateral Bipolar Transistor (LBJT), based on a minimally modified submicron MOSFET without gate oxide, was studied by means of simulations and measurements on fabricated devices. Large-tilt angle, single-sided implants were successfully used to control the breakdown voltage by tailoring an asymmetric collector doping profile and providing a lightly doped region on the collector side to increase the breakdown voltage. This was accomplished by using a base/gate pedestal as the mask for the large-tilt angle, single sided implantation in a self-aligned fashion. The individual collector–base and emitter–base junctions were found to be of excellent quality but, as expected due to the lack of carrier confinement in the base of devices built on bulk silicon, the common emitter current gain was lower than one. Two options enhancing the device performance were studied using simulators: building the LBJT on Silicon-on-Insulator (SOI) or introducing SiGe into the base. The SOI device promises to provide better performance and ease of processing when compared to the SiGe base device.

Optimization of SiGe HBTs for operation at high current densities

A comprehensive investigation of the impact of Ge profile shape as well as the scaling of collector and base doping profiles on high-injection heterojunction barrier effects in SiGe HBTs has been conducted over the -73-85/spl deg/C temperature range. The onset of Kirk effect at high current densities is shown to expose the Si/SiGe heterojunction in the collector-base space charge region, thereby inducing a conduction band barrier which negatively impacts the collector and base currents as well as the dynamic response, leading to a premature roll-off in both /spl beta/ and f/sub T/. In light of this, careful profile optimization is critical for emerging SiGe HBT circuit applications, since they typically operate at high current densities to realize maximum performance. We first explore the experimental consequences and electrical signature of these barrier effects over the 200-358 K temperature range for a variety of Ge profiles from an advanced UHV/CVD SiGe HBT technology. We then use extensive simulations which were calibrated to measured results to explore the sensitivity of these barrier effects to both the Ge profile shape and collector profile design, and hence investigate the optimum profile design points as a function of vertical scaling.

Modeling of the critical current density of bipolar transistors with retrograde collector doping profile

Advanced bipolar transistors used for high speed integrated circuits tend to drive high current density. As a result, base-widening occurs and device performance degrades. One of the methods to alleviate the base-widening is to form retrograde collector profiles. In this paper, we have derived for the first time the model of the critical current density of bipolar transistors with retrograde collector profiles. To verify the model, we performed extensively device simulation for two different collector profiles. Results from the model were compared with those of device simulation. The model derived shows a good agreement with device simulation over a V/sub CB/ bias range of 1-4 V.

Numerical Study of Collector-Base Junction Design for Ultra-High-Speed InP/InGaAs Heterojunction Bipolar Transistors

High-frequency operation of nonplanar and planar InP/InGaAs heterojunction bipolar transistors (HBTs) with various collector doping profiles has been investigated using a Monte Carlo particle simulation. It is shown that vertical scaling of the collector does not provide a substantial improvement in HBT overall speed performance due to the dramatic increase in the collector capacitance charging time with decreasing collector layer thickness. A considerable improvement in HBT high-frequency performance has been obtained in HBTs with buried subcollector and nonuniform collector doping profile.