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The objective of the proposed work is to study the behavior of SiGe HBTs at cryogenic temperatures and its relation to device scaling and optimization. Not only is cryogenic operation of these devices required by space missions, but characterizing their cryogenic behavior also helps to investigate the performance limits of SiGe HBTs and provides essential information for further device scaling. Technology computer aided design (TCAD) and sophisticated on-wafer DC and RF measurements are essential in this research. Drift-diffusion (DD) theory is used to investigate a novel negative differential resistance (NDR) effect and a collector current kink effect in first-generation SiGe HBTs at deep cryogenic temperatures. A theory of positive feedback due to the enhanced heterojunction barrier effect at deep cryogenic temperatures is proposed to explain such effects. Intricate design of the germanium and base doping profiles can greatly suppress both carrier freezeout and the heterojunction barrier effect, leading to a significant improvement in the DC and RF performance for NASA lunar missions. Furthermore, cooling is used as a tuning knob to better understand the performance limits of SiGe HBTs. The consequences of cooling SiGe HBTs are in many ways similar to those of combined vertical and lateral device scaling. A case study of low-temperature DC and RF performance of prototype fourth-generation SiGe HBTs is presented. This study summarizes the performance of all three prototypes of these fourth-generation SiGe HBTs within the temperature range of 4.5 to 300 K. Temperature dependence of a fourth-generation SiGe CML gate delay is also examined, leading to record performance of Si-based IC. This work helps to analyze the key optimization issues associated with device scaling to terahertz speeds at room temperature. As an alternative method, an fT -doubler technique is presented as an attempt to reach half-terahertz speeds. In addition, a roadmap for terahertz device scaling is given, and the potential relevant physics associated with future device scaling are examined. Subsequently, a novel superjunction collector design is proposed for higher breakdown voltages. Hydrodynamic models are used for the TCAD studies that complete this part of the work. Finally, Monte Carlo simulations are explored in the analysis of aggressively-scaled SiGe HBTs.

This dissertation describes the development of III-nitride (III-N) bipolar devices for optoelectronic and electronic applications. Research mainly involves device design, fabrication process development, and device characterization for Geiger-mode gallium nitride (GaN) deep-UV (DUV) p-i-n avalanche photodiodes (APDs), indium gallium nitride (InGaN)/GaN-based violet/blue laser diodes (LDs), and GaN/InGaN-based npn radio-frequency (RF) double-heterojunction bipolar transistors (DHBTs). All the epitaxial materials of these devices were grown in the Advanced Materials and Devices Group (AMDG) led by Prof. Russell D. Dupuis at the Georgia Institute of Technology using the metalorganic chemical vapor deposition (MOCVD) technique. Geiger-mode GaN p-i-n APDs have important applications in DUV and UV single-photon detections. In the fabrication of GaN p-i-n APDs, the major technical challenge is the sidewall leakage current. To address this issue, two surface leakage reduction schemes have been developed: a wet-etching surface treatment technique to recover the dry-etching-induced surface damage, and a ledged structure to form a surface depletion layer to partially passivate the sidewall. The first Geiger-mode DUV GaN p-i-n APD on a free-standing (FS) c-plane GaN substrate has been demonstrated. InGaN/GaN-based violet/blue/green LDs are the coherent light sources for high-density optical storage systems and the next-generation full-color LD display systems. The design of InGaN/GaN LDs has several challenges, such as the quantum-confined stark effect (QCSE), the efficiency droop issue, and the optical confinement design optimization. In this dissertation, a step-graded electron-blocking layer (EBL) is studied to address the efficiency droop issue. Enhanced internal quantum efficiency (ɳi) has been observed on 420-nm InGaN/GaN-based LDs. Moreover, an InGaN waveguide design is implemented, and the continuous-wave (CW)-mode operation on 460-nm InGaN/GaN-based LDs is achieved at room temperature (RT). III-N HBTs are promising devices for the next-generation RF and power electronics because of their advantages of high breakdown voltages, high power handling capability, and high-temperature and harsh-environment operation stability. One of the major technical challenges to fabricate high-performance RF III-N HBTs is to suppress the base surface recombination current on the extrinsic base region. The wet-etching surface treatment has also been employed to lower the surface recombination current. As a result, a record small-signal current gain (hfe) > 100 is achieved on GaN/InGaN-based npn DHBTs on sapphire substrates. A cut-off frequency (fT) > 5.3 GHz and a maximum oscillation frequency (fmax) > 1.3 GHz are also demonstrated for the first time. Furthermore, A FS c-plane GaN substrate with low epitaxial defect density and good thermal dissipation ability is used for reduced base bulk recombination current. The hfe > 115, collector current density (JC) > 141 kA/cm², and power density > 3.05 MW/cm² are achieved at RT, which are all the highest values reported ever on III-N HBTs.

Šiuolaikiniai Si/SiGe, AlGaAs/GaAs bei InGaP/GaAs įvarialyčiai dvipoliai tranzistoriai (ĮDT) pasižymi dideliu informacijos perdavimo greičiu, dideliu signalo stiprinimu, žemu triukšmų lygiu ir mažu signalo iškraipymu. Disertaciniame darbe atlikti Si/SiGe ir InGaP/GaAs ĮDT aukštadažnių charakteristikų ir triukšmo tyrimai dažnių ruože nuo 1 iki 30 GHz naudojant ir voltamperines charakteristikas. Tranzistorių triukšmų modeliavimas atliktas atsižvelgiant į tranzistoriaus šratinio triukšmo šaltinių koreliaciją, smūginę jonizaciją, tranzistoriaus parametrų temperatūrines priklausomybes. Dvipolių tranzistorių analitinis modelis, išvestas naudojant π –tipo ekvivalentinę grandinę, buvo įdiegtas į dvipolių tranzistorių kompaktinį (sutelktų parametrų) modelį HICUM (angl. high current model). Ši kompaktinio modelio versija gali aprašyti bazės ir kolektoriaus srovių šratinio triukšmo šaltinių koreliaciją. Kambario temperatūroje smūginės jonizacijos sąlygotas SiGe ĮDT triukšmo parametrų kitimas buvo tirtas hidrodinaminiu, dreifo - difuzijos ir kompaktiniu HICUM modeliais, taikant Chynowetho smūginės jonizacijos dėsnį griūtinių srovių įvertinimui. SiGe ĮDT temperatūriniai voltamperinių, aukštadažnių ir triukšmo charakteristikų tyrimai atlikti plačiame aplinkos temperatūrų ruože 4 – 423 K. Tyrimai parodė, kad hidrodinaminis ir kompaktinis HICUM modeliai galioja tik 300 – 423K temperatūrų ruože. / Modern Si/SiGe, AlGaAs/GaAs and InGaP/GaAs heterojunction bipolar transistors (HBTs) exhibit high-speed and high-frequency operation, high gain, low noise and low signal distortion. This work deals with an investigation of DC, microwave and noise characteristics of Si/SiGe and InGaP/GaAs HBTs in the relevant frrequency range of 1-30 GHz. Noise simulation and modeling of HBTs have been performed including correlation of shot noise sources, impact ionization and temperature dependences. Analytical model for bipolar transistor, based on π- type equivalent circuit was derived and implemented in the bipolar transistor compact model HICUM. This compact model HICUM version includes correlation between base and collector current noise sources. The noise behavior resulting from impact ionization was investigated at room temperature for SiGe HBTs. Modeling was performed with a hydrodynamic model, drift - diffusion models and the compact model HICUM using a Chynoweth’s law for avalanche generation. DC, high frequency characteristics and noise of SiGe HBTs were investigated in a wide ambient temperature range 4 – 423 K Both hydrodynamic device simulation and compact model HICUM view agreement with experimental data only in the temperature range of 300 – 423K.

Modern Si/SiGe, AlGaAs/GaAs and InGaP/GaAs heterojunction bipolar transistors (HBTs) exhibit high-speed and high-frequency operation, high gain, low noise and low signal distortion. This work deals with an investigation of DC, microwave and noise characteristics of Si/SiGe and InGaP/GaAs HBTs in the relevant frrequency range of 1-30 GHz. Noise simulation and modeling of HBTs have been performed including correlation of shot noise sources, impact ionization and temperature dependences. Analytical model for bipolar transistor, based on π- type equivalent circuit was derived and implemented in the bipolar transistor compact model HICUM. This compact model HICUM version includes correlation between base and collector current noise sources. The noise behavior resulting from impact ionization was investigated at room temperature for SiGe HBTs. Modeling was performed with a hydrodynamic model, drift - diffusion models and the compact model HICUM using a Chynoweth’s law for avalanche generation. DC, high frequency characteristics and noise of SiGe HBTs were investigated in a wide ambient temperature range 4 – 423 K Both hydrodynamic device simulation and compact model HICUM view agreement with experimental data only in the temperature range of 300 – 423K. / Šiuolaikiniai Si/SiGe, AlGaAs/GaAs bei InGaP/GaAs įvarialyčiai dvipoliai tranzistoriai (ĮDT) pasižymi dideliu informacijos perdavimo greičiu, dideliu signalo stiprinimu, žemu triukšmų lygiu ir mažu signalo iškraipymu. Disertaciniame darbe atlikti Si/SiGe ir InGaP/GaAs ĮDT aukštadažnių charakteristikų ir triukšmo tyrimai dažnių ruože nuo 1 iki 30 GHz naudojant ir voltamperines charakteristikas. Tranzistorių triukšmų modeliavimas atliktas atsižvelgiant į tranzistoriaus šratinio triukšmo šaltinių koreliaciją, smūginę jonizaciją, tranzistoriaus parametrų temperatūrines priklausomybes. Dvipolių tranzistorių analitinis modelis, išvestas naudojant π –tipo ekvivalentinę grandinę, buvo įdiegtas į dvipolių tranzistorių kompaktinį (sutelktų parametrų) modelį HICUM (angl. high current model). Ši kompaktinio modelio versija gali aprašyti bazės ir kolektoriaus srovių šratinio triukšmo šaltinių koreliaciją. Kambario temperatūroje smūginės jonizacijos sąlygotas SiGe ĮDT triukšmo parametrų kitimas buvo tirtas hidrodinaminiu, dreifo - difuzijos ir kompaktiniu HICUM modeliais, taikant Chynowetho smūginės jonizacijos dėsnį griūtinių srovių įvertinimui. SiGe ĮDT temperatūriniai voltamperinių, aukštadažnių ir triukšmo charakteristikų tyrimai atlikti plačiame aplinkos temperatūrų ruože 4 – 423 K. Tyrimai parodė, kad hidrodinaminis ir kompaktinis HICUM modeliai galioja tik 300 – 423K temperatūrų ruože.

In this thesis, a detailed study of the electrical and optical characterisations of Heterojuction Bipolar Transistors (HBTs) for optical detection is presented. By comparing both DC and optical characterisations between In0.49Ga0.51P/GaAs Single Heterojuction Bipolar Transistors (SHBTs) and Double Heterojuction Bipolar Transistors (DHBTs), the advantages of using the DHBT as a short wavelength detector are shown. Phenomena related to the base region energy band bending in the DHBT caused by a self-induced effective electric field is discussed and its effects on the performance of the device are elaborated. The use of an eye diagram has been employed to provide requisite information for performance qualification of SHBT/DHBT devices. These give a more detailed understanding compared to conventional S-parameters method. A detailed comparison of In0.49Ga0.51P/GaAs SHBT and DHBT performance using an eye diagram as a functional tool by adopting a modified T-shaped small signal equivalent circuit are given. By adopting this modified T-shaped small signal equivalent circuit, the use of In0.49Ga0.51P/GaAs Double Heterojuction Phototransistors (DHPT) as a short wavelength photodetector is analysed. It is therefore shown that an eye diagram can act as a powerful tool in HBTs/HPTs design optimisations, for the first time in this work. In order to predict the spectral response (SR) and optical characterisations of GaAs-based HPTs, a detailed theoretical absorption model is also presented. The layer dependence of an optical flux absorption profile, along with doping dependent absorption coefficients are taken into account for the optical characterisation prediction. With the aim of eliminating the limitation of current gain as a prerequisite, analytical modelling of SR has been developed by resolving the continuity equation and applying realistic boundary conditions. Then, related physical parameters and a layer structure profile are used to implement simulations. A good agreement with the measured results of the Al0.3Ga0.7As/GaAs HPT is shown validating the proposed theoretical model.

The large unlicensed 3 GHz overlapping bandwidth that is available worldwide at 60 GHz has resulted in renewed interest in 60 GHz technology. This frequency band has made it attractive for short-range gigabit wireless communication. The power amplifier (PA) directly influences the performance and quality of this entire communication chain, as it is one of the final subsystems in the transmitter. Spectral efficient modulation schemes used at 60 GHz pose challenging requirements for the linearity of the PA. To improve the linearity, several external linearisation techniques currently exist, such as feedback, feedforward, envelope elimination and restoration, linear amplification with non-linear components and predistortion. This thesis is aimed at investigating and characterising the distortion components found in PAs at mm-wave frequencies and evaluating whether an adaptive predistortion (APD) linearisation technique is suitable to reduce these distortion components. After a thorough literature study and mathematical analysis, it was found that the third-order intermodulation distortion (IMD3) components were the most severe distortion components. Predistortion was identified as the most effective linearisation technique in terms of minimising these IMD3 components and was therefore proposed in this research. It does not introduce additional complexity and can easily be integrated with the PA. Furthermore, the approach is stable and has lower power consumption when compared to the aforementioned linearisation techniques. The proposed predistortion technique was developed compositely through this research by making it a function of the PA’s output power that was measured using a power detector. A comparator was used with the detected output power and the reference voltages to control the dynamic bias circuit of the variable gain amplifier. This provided control and flexibility on when to apply the predistortion to the PA and therefore allowing the linearity of the PA to be optimised. Three-stage non-linear and linear PAs were also designed at 60 GHz and implemented to compare the performance of the APD technique and form part of the hypothesis verification process. The 130 nm silicon-germanium (SiGe) bipolar and complementary metal oxide semiconductor (BiCMOS) technology from IBM was used for the simulation of the entire APD and PA design and for the fabrication of the prototype integrated circuits (ICs). This technology has the advantage of integrating the high performance, low power intensive SiGe heterojunction bipolar transistors (HBTs) with the CMOS technology. The SiGe HBTs have a high cut-off frequency (fT > 200 GHz), which is ideal for mm-wave PA applications and the CMOS components were integrated in the control logic of the digital circuitry. The simulations and IC layout were accomplished with Cadence Virtuoso. The implemented IC occupies an area of 1.8 mm by 2.0 mm. The non-linear PA achieves a Psat of 11.97 dBm and an IP1dB of -10 dBm. With the APD technique applied, the linearity of the PA is significantly improved with an IP1dB of -6 dBm and an optimum IMD3 reduction of 10 dB. Based on the findings and results of the applied APD technique, APD reduced intermodulation distortion (especially the IMD3) and is thus suitable to improve the linearity of PAs at mm-wave frequencies. To the knowledge of this author, no APD technique has been applied for PAs at 60 GHz, therefore the contribution of this research will assist future PA designers to characterise and optimise the reduction of the IMD3 components. This will result in improved linear output power from the PA and the use of complex modulation schemes at 60 GHz. / Thesis (PhD)--University of Pretoria, 2014. / Electrical, Electronic and Computer Engineering / PhD

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Le travail porte sur le développement et l’optimisation de transistors bipolaires à hétérojonction (TBH) SiGe et SiGeC par conception technologique assistée par ordinateur (TCAD). L'objectif est d'aboutir à un dispositif performant réalisable technologiquement, en tenant compte de tous les paramètres : étapes de fabrication technologiques, topologie du transistor, modèles physiques. Les études menées permettent d’atteindre les meilleures performances, en particulier une amélioration importante de la fréquence maximale d’oscillation (fMAX). Ce travail est la première approche développée pour la simulation des TBH SiGeC qui prend en compte l'impact de la contrainte et de la teneur en germanium et en carbone dans la base; conjointement pour les simulations des procédés de fabrication et les simulations électriques.Pour ce travail, nous avons développé et implémenté dans le simulateur TCAD des méthodes d'extraction de fMAX prenant en compte les éléments parasites intrinsèques et extrinsèques. Nous avons développé et implémenté un modèle pour la densité effective d’états fonction de la teneur en germanium et en carbone dans la base. Les modèles pour la bande interdite, la mobilité et le temps de relaxation de l'énergie sont calibrés sur la base de simulations Monte-Carlo.Les différentes analyses présentées dans cette thèse portent sur six variantes technologiques de TBH. Trois nouvelles architectures de TBH SiGeC avancés ont été élaborées et proposées pour des besoins basse et haute performance. Grace aux résultats obtenus, le meilleur compromis entre les différents paramètres technologiques et dimensionnels permettent de fabriquer un TBH SiGeC avec une valeur de fMAX de 500 GHz, réalisant ainsi l’objectif principal de la thèse. / The present work investigates the technology development of state-of-the-art SiGe and SiGeC Heterojunction Bipolar Transistors (HBT) by means of technology computer aided design (TCAD). The objective of this work is to obtain an advanced HBT very close to the real device not only in its process fabrication steps, but also in its physical behavior, geometric architecture, and electrical results. This investigation may lead to achieve the best electrical performances for the devices studied, in particular a maximum operating frequency of 500 GHz. The results of this work should help to obtain more physical and realistic simulations, a better understanding of charge transport, and to facilitate the development and optimization of SiGe and SiGeC HBT devices.The TCAD simulation kits for SiGe/SiGeC HBTs developed during our work have been carried out in the framework of the STMicroelectronics bipolar technology evolution. In order to achieve accurate simulations we have used, developed, calibrated and implemented adequate process models, physical models and extraction methodologies. To our knowledge, this work is the first approach developed for SiGe/SiGeC HBTs which takes into account the impact of the strain, and of the germanium and carbon content in the base, for both: process and electrical simulations.In this work we will work with the successive evolutions of B3T, B4T and B5T technologies. For each new device fMAX improves of 100 GHz, thus the technology B3T matches to 300 GHz, B4T and B5T to 400 and 500 GHz, respectively.Chapter one introduces the SiGe SiGeC heterojunction bipolar technologies and their operating principles. This chapter deals also with the high frequency AC transistor operation, the extraction methods for fMAX and the carrier transport in extremely scaled HBTs.Chapter two analyzes the physical models adapted to SiGeC strained alloys used in this work and the electrical simulation of HBT devices. This is also an important work of synthesis leading to the selection, implementation and development of dedicated models for SiGeC HBT simulation.Chapter three describes the B3T TCAD simulation platform developed to obtain an advanced HBT very close to the real device. In this chapter the process fabrication of the B3T technology is described together with the methodology developed to simulate advanced HBT SiGeC devices by means of realistic TCAD simulations.Chapter four describes the HBT architectures developed during this work. We will propose low-cost structures with less demanding performance requirements and highly performing structures but with a higher cost of production. The B4T architecture which has been manufactured in clean-room is deeply studied in this chapter. The impact of the main fabrication steps is analyzed in order to find the keys process parameters to increase fMAX without degrading other important electrical characteristics. At the end of this chapter the results obtained is used to elaborate a TCAD simulation platform taking into account the best trade-off of the different key process parameters to obtain a SiGeC HBT working at 500 GHz of fMAX.

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