PLANAR Gaas GUNN and FIELD EFFECT DEVICES by TREVOR
Total Page：16
File Type：pdf, Size：1020Kb
PLANAR GaAs GUNN AND FIELD EFFECT DEVICES by TREVOR WILLIAM TUCKER B.A.Sc. University of British Columbia, 1964 M.A.Sc. University of British Columbia, 1966 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of Electrical Engineering We accept this thesis as conforming to the required standard. THE UNIVERSITY OF BRITISH COLUMBIA July, 1972 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference arid study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of ETi.fe C fe-K< C- The University of British Columbia Vancouver 8, Canada Date ( < ^eLPT 7£ ABSTRACT Two types of devices, planar Gunn diodes and the negative resistance field effect transistors, have been investigated. Their fabrication, testing and properties are discussed. For the planar diode the Gunn domain velocity is predicted analytically and shown experimentally to decrease with, decreasing product of carrier concentration and diode thickness. A particular structure of GaAs FET which displays a static negative differential resistance (SNDR) characteristic without Gunn instability has been made. The mechanism of the SNDR is discussed and the device's uses in a number of circuits (oscillator, amplifier, phase- locked oscillator and bistable logic element) are described. i TABLE OF CONTENTS Page ABSTRACT i TABLE OF CONTENTS ii LIST OF ILLUSTRATIONS ' v ACKNOWLEDGEMENT x I. INTRODUCTION 1 II. PLANAR GUNN DIODES 4 2.1 Introduction 4 2.2 Background 5 2.2.1 Oscillation in Experimental Planar Gunn-Diodes 5 2.2.2 Oscillation Suppression in Bulk Gunn Diodes . 9 2.2.3 Properties of Subcritically Doped Bulk Diodes . 11 2.2.4 Analyses of Oscillation Suppression in Thin Diodes 12 2.2.5 Planar Diodes with Surface Capacitive Loading . 19 2.2.6 Experimentally Observed Oscillation Suppression in Thin and Dielectrically Loaded Diodes . 20 2.3 Small Signal Analysis of the Thin Gunn Diode -23 2.3.1 G\mn Domain Velocity in a Thin Gunn Diode ... 28 2.3.2 Condition for Zero Domain Velocity in a Thin Gunn Diode 31 2.3.3 Oscillation Suppression in Thin Gunn Diode . 33 2.4 Oscillation Suppression in a Capacitively-Loaded Thin Gunn Diode 36 III. DEVICE FABRICATION 39 3.1 Introduction 39 3.2 Photographic Reduction . 39 3.3 Photoresist and Etching Techniques 40 3.4 Electrical Contacts 43 3.4.1 Influence of Contacts •• . 43 3.4.2 GaAs Cleaning 47 3.4.3 The Alloying Cycle 48 3.4.4 Low Field Contact Resistance 50 3.4.5 Current-Voltage Characteristics 54 3.4.6 The High Resistance Contact Layer. 56 3.4.7 Impact Ionization Noise Spectrum 58 3.4.8 Anode Light Emission 62 3.4.9 Anode Metal Migration and Device Failure ... 66 3.5 Device Mounting 68 ii Page IV. PLANAR GUNN DIODE EXPERIMENTAL APPARATUS AND RESULTS .... 70 4.1 Introduction 70 4.2 Test Apparatus . 70 4.2.1 Diode Coaxial Holder 70 4.2.2 Test Circuit 72 4.2.3 Device Geometries 74 4.3 GaAs Properties . 76 4.4 Domain Velocity in Planar Gunn Diodes . 80 4.4.1 Dependence on the nd Product 80 4.4.2 Bias Tuning of Uniform Gunn Diodes 84 4.4.3 Bias Tuning of Tapered Gunn Diodes 86 V. THE NEGATIVE RESISTANCE FIELD EFFECT TRANSISTOR (NERFET) . 89 5.1 Introduction 89 5.2 The Construction and Characteristics of the NERFET . 89 5.2.1 NERFET Structure and Fabrication 89 5.2.2 NERFET Characteristics 99 5.3 Related Devices 119 5.3.1 Introduction . s ...... 119 5.3.2 Conventional GaAs FETs . 127 5.3.3 GaAs FETs with Negative Resistance Effects . 128 5.3.4 Gunn Devices with Three Electrodes 132 5.3.5 Other GaAs Devices with SNDR 133 5.4 On the Static Negative Differential Resistance (SNDR) Mechanism ....... 134 5.4.1 Introduction 134 5.4.2 Thermal Effects and the NERFET Switching Speed 135 5.4.3 Travelling Gunn Domain Effects 138 5.4.4 Effect of the p-n Junction . 139 5.4.5 Other Aspects of the SNDR Phenomenon 141 5.4.6 Previous Theories of Bulk SNDR 145 5.5 Circuit Performance of the NERFET 148 5.5.1 Introduction 148 5.5.2 The NERFET Equivalent Circuit . 148 5.5.3 Small Signal Analysis 151 5.5.4 Non-linear Analysis 156 5.5.5 Relaxation Oscillation Analysis 162 5.5.6 The NERFET as a Gate Tunable Oscillator .... 164 5.5.7 The NERFET as a Phase Locked Oscillator and as a Stable Amplifier 168 5.5.8 The NERFET as a Bistable Logic Element .... 169 VI. CONCLUSIONS 173 iii Page 6.1 The Planar Gunn Diode 173 6.2 The NERFET 174 •{ v LIST OF ILLUSTRATIONS Figure Page 1.1 a) The sandwich, structure and b) the planar struc• ture 1 2.1 The domain velocities observed by previous workers 7 2.2 Current-voltage characteristic of a sub-critically doped diode 12 2.3 Cross-section of a thin film diode 23 2.4 The sign convention 23 14 2.5 Dispersion curves for (a) n = 2 x 10 and (b) n = 15 -3 2 x 10 cm 29 2.6 Domain velocity (normalized to the carrier drift velocity) as a function of diode thickness and surface loading ... 30 2.7 The growth factor 3"L as a function of a for various £II diode lengths and carrier concentrations . 34 2.8 Cross-section of a th-in film 'diode -with -surface capaci-t-ive loading 36 3.1 The micropositioner 41 3.2 A typical diode 42 3.3 A typical alloying cycle 49 3.4 Globules of Au-Ge after alloying 50 3.5 Bevel showing filament penetration into GaAs 51 3.6 Contact resistance as a function of alloying temperature . 52 3.7 Contact resistance as a function of alloying time 53 3.8 I-V characteristic of a coherent diode 55 3.9 I-V characteristic of an incoherent diode ......... 55 3.10 Waveform with both coherent and incoherent components ... 56 3.11 I-V characteristic of a diode whose waveform has both co• herent and incoherent components 57 3.12 Potential distribution along a diode with poor contacts . 59 v Figure Page 3.13 Electric field distribution along a diode with poor contacts 59 3.14 Noise spectrum of a diode biased slightly above the. threshold voltage 60 3.15 Noise spectrum of a diode biased at twice the threshold voltage ........ 61 3.16 Diode showing emitted light at the anode 62 3.17 Light spectrum measurement system . 63 3.18 Spectrum of emitted light at the anode of a GaAs diode ... 64 3.19 Radiation intensity dependence on applied voltage 65 3.20 Metal migration and anode light emission from a device undergoing breakdown 67 3.21 Bevel across a conducting filament after breakdown 68 3.22 A mounted diode 69 .4.1 Diode mount and holder . ........ 71 4.2 VSWR measurement circuit 72 4.3 The diode test circuit 73 4.4 Diode geometries studied . 75 4.5 Edge view of the holder used for bevelling 77 4.6 The van der Pauw clover leaf geometry 78 4.7 Carrier concentration profiles 79 4.8 Hall mobility profiles 79 4.9 Gunn mode current waveform 80 4.10 Correlation of current waveform to diode shape 81 4.11 Domain velocity in thin Gunn diodes as a function of nd product 82 4.12 Bias tuning of a uniform Gunn diode 85 4.13 A tapered diode 86 4.14 Bias tuning of a tapered diode 87 \7T Figure Page 5.1 Types of NERFET geometries in cross-section 91 5.2 Capacitance-voltage measurement circuit 92 5.3 Typical capacitance-voltage characteristic for a reverse biased p-n junction 93 5.4 Electron concentration profiles measured by C-V and Hall methods 94 5.5 Typical p-n junction current-voltage characteristic .... 96 5.6 A bevelling and stained p-n junction 96 5.7 NERFET structure 98 5.8 NERFET typical I-V characteristics 98 5.9 The current-voltage characteristics of a tunnel diode a) with circuit stability and b) with circuit insta• bility (from Chow 1964) 99 5.10 The current-voltage characteristic of a NERFET in a) stable circuit operation b) and c) unstable circuit operation 100 5.11 ' Current-voltage test circuit 100 5.12 Current-voltage characteristic of a NERFET which apparently produced coherent GHz oscillation in a resistive circuit. 101 5.13 GHz oscillation from a NERFET in a resistive circuit . 101 5.14 Current-voltage characteristic of a NERFET which produced incoherent GHz oscillation in a resistive circuit .... 102 5.15 The current-voltage characteristic of a NERFET a) before and b) after a step was etched into the source end . 103 5.16 I-V characteristics for three device thicknesses 105 5.17 Normalized I-V characteristic of a junction FET in terms of the parameter I /I describing velocity saturation . 110 r op 5.18 Representation of the cross section of a notched NERFET . 110 5.19 Match of experimental and theoretical I-V characteristics for a NERFET 114 5.20 Cross-section of a NERFET 114 5.21 Hysteresis growth after illumination ceases 116 vii Figure Page 5.22 Circuit used to measure KTFR properties 117 5.23 Variation of KTFR properties with drying 118 5.24 Hysteresis variation with drying time of a KTFR covered NERFET 120 5.25 Compilation of related devices 122 5.26 Tuning characteristic as a function of p-region bias (from Petzinget, Hahn and Matzelle 1967) 130 5.27 NERFET switching speed circuit 136 5.28 NERFET switching'waveforms .