THE UNIVERSITY OF MANCHESTER Highly Sensitive Nano Tesla Quantum Well Hall Effect Integrated Circuits using GaAs-InGaAs-AlGaAs 2DEG A thesis submitted to The University of Manchester for the degree of Doctor of Philosophy In the faculty of Engineering and Physical Sciences 2015 Mohammadreza Sadeghi School of Electrical and Electronic Engineering 1 Institute: School of EEE, the University of Manchester Candidate: Mohammadreza Sadeghi Degree: Doctor of Philosophy (PhD) Title: Highly Sensitive Nano Tesla Quantum Well Hall Effect Integrated Circuits using GaAs-InGaAs-AlGaAs 2DEG Date: February 2015 Abstract Hall Effect integrated circuits are used in a wide range of applications to measure the strength and/or direction of magnetic fields. These sensors play an increasingly significant role in the fields of automation, medical treatment and detection thanks largely to the enormous development of information technologies and electronic industries. Commercial Hall Effect ICs available in the market are all based on silicon technology. These ICs have the advantages of low cost and compatibility with CMOS technology, but suffer from poor sensitivity and detectability, high power consumption and low operating frequency bandwidths. The objective of this work was to develop and fabricate the first fully monolithic GaAs- InGaAs-AlGaAs 2-Dimensional Electron Gas (2DEG) Hall Effect integrated circuits whose performance enhances pre-existing technologies. To fulfil this objective, initially 2 µm gate length pHEMTs and 60/20 µm (L/W) Greek cross Hall Effect sensors were fabricated on optimised GaAs-In.18Ga.82As-Al.35Ga.65As 2DEG structures (XMBE303) suitable for both sensor and integrated circuit designs. The pseudomorphic high electron mobility transistors (pHEMTs) produced state-of-the-art output conductance, providing high intrinsic gain of 405, current cut-off frequency of 4.8 GHz and a low negative threshold voltage of -0.4 V which assisted in designing single supply ICs with high sensitivity and wide dynamic range. These pHEMTs were then accurately modelled for use in the design and simulation of integrated circuits. The corresponding Hall sensor showed a current sensitivity of 0.4 mV/mA.mT and a maximum magnetic DC offset of 0.35 mT at 1 V. DC digital (unipolar) and DC linear Hall Effect integrated circuits were then designed, simulated, fabricated and fully characterised. The DC linear Hall Effect IC provided an overall sensitivity of 8 mV/mT and a power consumption as low as 6.35 mW which, in comparison with commercial Si DC linear Hall ICs, is at least a factor of 2 more power efficient. The DC digital (unipolar) Hall Effect IC demonstrated a switching sensitivity of 6 mT which was at least ~50% more sensitive compared to existing commercial unipolar Si Hall ICs. In addition, a novel low-power GaAs-InGaAs-AlGaAs 2DEG AC linear Hall Effect integrated circuit with unprecedented sensitivity and wide dynamic range was designed, simulated, fabricated and characterised. This IC provided a sensitivity of 533 nV/nT, minimum field detectability of 177 nT (in a 10 Hz bandwidth) at frequencies from 500 Hz up to 200 kHz, consuming only 10.4 mW of power from a single 5 V of supply. In comparison to commercial Si linear Hall ICs, this IC provides an order of magnitude larger sensitivity, a factor of 4 higher detectability, 20 times wider bandwidth and over 20% lower power consumption (10.4 mW vs. 12.5 mW). These represent the first reported monolithic integrated circuits using a CMOS-like technology but in GaAs 2DEG technology and are extremely promising as complements, if not alternatives, to CMOS Si devices in high performance applications (such as high temperatures operations (>150 °C) and radiation hardened environment in the nuclear industry). 2 DECLARATION No portion of the work referred to in the thesis has been submitted in support of an application for another degree or qualification of this or any other university or other institute of learning. COPYRIGHT STATEMENTS The author of this dissertation (including any appendices to this dissertation) owns any copyright in it (the “Copyright”) and he has given The University of Manchester the right to use such Copyright for any administrative, promotional, educational and teaching purposes. Copies of this dissertation, either in full or in extracts, may be made only in accordance with regulations of the John Rylands University Library of Manchester. Details of these regulations may be obtained from the Librarian. This page must form part of any such copies. The ownership of any patents, designs, trademarks and any and all other intellectual property rights except for the Copyright(the “Intellectual Property Rights”) and any reproductions of copyright works, for example graphs and tables (“Reproductions”), which may be described in this dissertation, may not be owned by the author and may owned by third parties. Such Intellectual Property Rights and Reproductions cannot and must not be made available for use without the prior written permission of the owner(s) of the relevant Intellectual Property Rights and Reproductions. Further information on the conditions under which disclosure, publication and exploitation of this dissertation, the Copyright and any Intellectual Property Rights and Reproductions described in it may take place is available from the Head of School of Electrical and Electronic Engineering. 3 ACKNOWLEDGEMENTS Praise to God for giving me the most caring family as well as health, energy, motivation, patience and guiding me throughout my PhD. I would like to give the deepest gratitude and appreciations to my supervisor Professor Mohamed Missous for his fantastic support and great guidance during this PhD. I am very proud to have worked with such a knowledgeable, experienced, supportive, encouraging and well known scholar. Secondly, I would like to thank our experimental officer, Dr. James Sexton for his continuous effort in maintaining the cleanroom facilities at the highest standards and for all his professional and helpful advices, support and assistances. Furthermore, I would like to thank the Head of EEE School, Professor Tony Brown and the head of SISP group, Professor Krikor Ozanyan for their great support and all the staff in the SISP and M&N groups, in particular Dr Yan Lai, Mr Malachy Mcgowan and Mr. John Bailey, for their useful discussions, friendliness and helpful advices. Finally, I would like to give the heartiest thanks to my parents for their enormous support, great understanding and sacrifices throughout my PhD. Without their support, this work would have been incomplete. 4 DEDICATION This thesis is dedicated to my caring parents, my loving grandparents (RIP) and my kind twin sisters. 5 Table of Contents 1 Introduction ................................................................................................................. 21 1.1 Overview of the research ....................................................................................... 21 1.2 Aims and objectives .............................................................................................. 22 1.3 Achievements and contributions of this research project........................................ 22 1.4 Thesis outline ........................................................................................................ 23 2 Literature Review ........................................................................................................ 25 2.1 Introduction to III-V compound semiconductor devices ........................................ 25 2.2 Homojunctions and Heterojunctions ...................................................................... 26 2.3 Lattice constant and lattice matched materials ....................................................... 26 2.4 Band discontinuity ................................................................................................ 28 2.5 Quantum well and formation of 2DEG .................................................................. 28 2.6 Bulk and -doped layers ........................................................................................ 29 2.7 Metal to semiconductor interfaces ......................................................................... 30 2.7.1 Schottky contact............................................................................................. 31 2.7.2 Ohmic contact ................................................................................................ 32 2.8 High-speed transistors ........................................................................................... 32 2.8.1 High Electron Mobility Transistor (HEMT) ................................................... 33 2.8.2 Pseudomorphic High Electron Mobility Transistor (pHEMT) ........................ 34 2.8.3 HEMT/pHEMT theory of operation ............................................................... 35 2.9 Summary .............................................................................................................. 38 3 Magnetism and Magnetic Sensors................................................................................ 39 3.1 Introduction .......................................................................................................... 39 3.2 Magnetic Field Generation .................................................................................... 39 3.3 Magnetic sensors ................................................................................................... 40 3.3.1 Search