Zusammenfassung ................................................. I
1 Introduction ................................................. 1
1.1 Biosensor concepts ...................................... 2
1.2 Group III-nitrides for biosensing applications .......... 4
1.3 Scope of this work ...................................... 9
2 Chemical functionalization of group III-nitrides ............ 11
2.1 Introduction to organic monolayers ..................... 12
2.1.1 Concept of self-assembled monolayers ............ 12
2.1.2 Silanization .................................... 14
2.2 Surface pretreatment - OH-termination of GaN and AlN ... 17
2.2.1 Hydroxylation methods and sample preparation .... 18
2.2.2 Analysis of hydroxylated group III-nitrides ..... 19
2.3 APTES-modified GaN and AlN surfaces .................... 32
2.3.1 APTES SAM formation ............................. 32
2.3.2 Structural and chemical analysis ................ 33
2.4 ODTMS-modified GaN and A1N surfaces .................... 49
2.4.1 SAM formation ................................... 50
2.4.2 Structural and chemical analysis ................ 50
2.5 Photolysis of silane SAMs .............................. 61
2.5.1 Micropatterned silane SAMs on GaN ............... 62
2.5.2 UV-induced degradation of ODTMS SAMs on GaN ..... 63
2.6 Conclusion ............................................. 69
3 Immobilization of biofunctional layers ...................... 71
3.1 Coupling via Schiff-base formation ..................... 72
3.2 Attachment of Oligo-nucleotides on GaN ................. 73
3.3 Enzymes immobilized on GaN ............................. 74
3.3.1 Enzyme function ................................. 76
3.3.2 Kinetics of enzyme-catalyzed reactions .......... 76
3.3.3 Immobilization of enzymes on GaN ................ 78
3.3.4 Activity of immobilized penicillinase ........... 82
3.4 Conclusion ............................................. 89
4 Electronic properties of silane SAMs on GaN ................. 93
4.1 Molecular interactions with semiconductor surfaces ..... 95
4.1.1 Semiconductor surfaces .......................... 95
4.1.2 Chemisorbed molecules ........................... 97
4.2 MIS-junctions .......................................... 99
4.2.1 Carrier transport mechanisms in Schottky
diodes .......................................... 99
4.2.2 Electronic conduction through SAMs ............. 103
4.2.3 Capacitance-voltage measurements ............... 104
4.3 Electrical characterization of ODTMS-modified GaN ..... 106
4.3.1 I-U characteristics ............................ 107
4.3.2 Capacitance-voltage characteristics ............ 114
4.4 Impact of UV illumination on electronic properties .... 119
4.5 Conclusion ............................................ 122
5 Enzyme modified AlGaN/GaN FETs ............................. 123
5.1 Review ................................................ 125
5.2 Detection mechanism ................................... 126
5.3 Electrochemical measurement setup ..................... 128
5.4 Penicillinase modified AlGaN/GaN EGFETs ............... 129
5.4.1 Processing of transducer devices ............... 129
5.4.2 Immobilization of penicillinase ................ 130
5.4.3 Characterization of functionalized AlGaN/GaN
EGFETs ......................................... 132
5.5 Electronic response of enzymatic reaction ............. 136
5.5.1 Transient response ............................. 136
5.5.2 Response characteristics of c-EnFETs and
p-EnFETs ....................................... 140
5.6 Kinetic model of pH-based EnFETs ...................... 143
5.6.1 Review ......................................... 143
5.6.2 Proposed model ................................. 145
5.6.3 Summary ........................................ 156
5.7 Experimental verification of the proposed model ....... 157
5.7.1 Influence of enzyme kinetics ................... 157
5.7.2 Influence of relative mass transport ........... 161
5.7.3 Influence of buffer concentration .............. 163
5.7.4 Influence of pH of analyzed test solution ...... 164
5.7.5 Summary ........................................ 167
5.8 Stability of penicillinase-AlGaN/GaN EGFETs ........... 168
5.8.1 Degradation .................................... 169
5.8.2 Stabilized enzyme layer ........................ 170
5.8.3 Lifetime factors ............................... 171
5.8.4 Summary ........................................ 174
5.9 Conclusion ............................................ 175
6 Summary and Outlook ....................................... 177
Appendix - Experimental setups ................................ 183
References .................................................... 188
List of Publications .......................................... 211
Acknowledgements .............................................. 213
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