Index
Introduction . . . . 1
Scaling–down of CMOS technology . . . . 2
Mesoscopic systems . . . . 3
Quantum point contacts . . . . 4
The transistor effect . . . . 6
Fabrication of the devices and measurements . . . . 7
Bibliography . . . . 8
1. Voltage gain in ballistic nanoelectronic devices . . . 10
1.1 Introduction . . . 10
1.2 Basics of mesoscopic physics . . . 11
1.2.1 Length and energy scales . . . 12
1.2.2 The two–dimensional electron gas . . . 14
1.2.3 Electronic transport regimes . . . 19
1.2.4 Basics of quantum mechanics . . . 20
1.2.5 Low dimensional systems . . . 22
1.3 Quantum point contacts . . . 25
1.4 The linear regime in 1D ballistic conductors . . . 27
1.5 The no–linear regime in 1D ballistic conductors . . . 32
Bibliography . . . 36
2. Design and fabrication . . . 38
2.1 Introduction . . . 38
2.2 Substrate . . . 39
2.2.1 Molecular beam epitaxy . . . 40
2.2.2 Wafer parameters . . . 41
2.3 Layout definition . . . 42
2.3.1 Pattern design with L-Edit . . . 43
2.3.2 Device configurations . . . 44
2.3.3 Marks . . . 50
2.4 Electron beam lithography . . . 51
2.4.1 EBL system . . . 52
2.4.2 Preparation for exposure . . . 56
2.4.3 Exposure parameters . . . 57
2.4.4 After exposure . . . 58
2.5 Technological processes . . . 59
2.5.1 Wafer marks . . . 59
2.5.2 Mesa . . . 60
2.5.3 Ohmic contacts . . . 63
2.5.4 Split gates . . . 65
2.5.5 Protection with an insulator . . . 66
2.5.6 Metallic connection . . . 67
2.6 Dose and position testing for the split gates . . . 68
2.7 Final steps . . . 70
Bibliography . . . 73
3. Measurements and results . . . 75
3.1 Low temperature measurements . . . 75
3.2 Setup and procedures for the measurement . . . 77
3.2.1 Source Monitor Unit and DC parametric analyzer . . . 80
3.3 Electrical characterization . . . 84
3.3.1 Characteristics of the first set of produced devices . . . 85
3.3.2 Characteristics of the second set of produced devices . . . . 89
3.4 Voltage gain calculation . . . 93
3.5 Conclusions . . . 99
Conclusions . . . . 101
