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Title of Thesis

Tauseef Ahmed Khan
Institute/University/Department Details
Faculty of Engineering Sciences/ Ghulam Ishaq Khan Institute of Engineering Sciences and Technology
Engineering Sciences
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
organic semiconductor, copper phthalocyanine, photoelectric sensors, photocapacitive sensors, humidity sensors, organic-inorganic heterojunctions, organic semiconductor devices

This work describes fabrication of organic semiconductor devices such as humidity and light sensors based on organic semiconductor, and an investigation into temperature dependent properties of organic-inorganic heterojunctions. Recently organic semiconductors have obtained considerable interest in the fields of electronic and photonic devices due to a wide range of applications as low cost, large area and disposable electronics on thin and flexible substrates. Their low cost production is very simple using recent high vacuum evaporation and spin coating technology. However, the response of organic semiconductor devices at different temperatures in terms of charge transport mechanism is not fully investigated. This work therefore concentrated on the Fabrication of organic semiconductor devices based on copper phthalocyanine (CuPc), and temperature dependent properties of organic-inorganic heterojunctions.

Ag/CuPc/GaAs/ Ag junctions were fabricated and their electric and photoelectric properties were examined in differential mode of operation i.e. by exposing only a small area of the sensor to light. A thin film of CuPc was deposited on GaAs substrate to Fabricate Ag/n-GaAs/p-CuPc/Ag structure in which the front electrode had gradient of thickness. Thus, 6% and 10% of the incident light can be transmitted through the silver film at the edge and in the center of the sample respectively. Open circuit voltage and short circuit current were measured by exposing only a small area of the sensor to light. It was observed that both depends on position of the exposed area of the sensor to light. Thus the sensor may be used as a photoelectric displacement transducer.

Organic phototransistor based on CuPc, and photo capacitive sensor based on poly-N-epoxypropylcarbazole complexes were fabricated and investigated. Capacitive humidity and light sensor was fabricated by depositing thin film of CuPc on glass substrate with silver surface type electrodes to form Ag/CuPc/Ag structure. The sensor was sensitive to humidity as well as light. The capacitance of the sample was evaluated at room temperature in the relative humidity range of 35-92%. It was observed that the capacitance of the sensor increases with increase in humidity. The ratio of the relative capacitance to relative humidity was equal in average to 200. It was observed that under filament lamp illumination up to 1000 1x the capacitance of the photo capacitive detectors increased continuously up to 20% as compared to dark conditions.

To investigate the properties of CuPc based sensors; Ag/CuPc/GaAs/ Ag junctions were Fabricated and their electric and photoelectric properties were examined in a wide temperature range of 82 to 350 K. Different electrical parameters to be used in the understanding of the junctions were evaluated and an equivalent circuit of the junction has been developed. Experimental data revealed that the fabricated junctions could be used as photo sensors for the NIR-UV spectral region.

Changes in processing conditions can change properties of organic materials. In order to increase mobility, denser and more effective electron intermolecular transfer structures should be developed. Centrifugal processing of these materials is very promising because of weak molecular bonding, and because of the high molecular weight of organic semiconductors. Thickness distribution of thin organic films of CuPc deposited by vacuum evaporation on glass substrates at different gravity conditions, from 50g to -50g, were investigated. An anisotropic distribution of the film was observed in the direction of source and substrate rotation. In a direction perpendicular to the rotation, the distribution of thickness was isotropic and obeyed, in principle, the theoretical approach which requires a maximum distribution at the center of the sample.

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13352.01 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
1222.55 KB
2 1 Introduction 1
925.92 KB
  1.1 Basic Properties Of Organic Semiconductors 1
  1.2 Organic Semiconductor Devices 3
  1.3 Organic Semiconductors In Senor Technology 7
  4.4 Outline Of The Dissertation 7
  4.5 References 9
3 2 Theory & Literature Review 10
2544.43 KB
  2.1 Review Literature 10
  2.2 Theoretical Background 18
4 3 Experimental Setup 35
519.84 KB
  3.1 Introduction 35
  3.2 Device Fabrication 35
  3.3 Experimental Setup For Characterization 39
  3.4 References 42
5 4 Differential Response Of Cupc/Gaas 43
1509.1 KB
  4.1 Introduction 43
  4.2 Experimental 45
  4.3 Results And Discussion 47
  4.4 Conclusion 58
  4.5 References 59
6 5 Effect Of High Gravity On Physical Vapor Deposition Of Cupc 62
1107.41 KB
  5.1 Introduction 62
  5.2 Experimental 63
  5.3 Results And Discussion 66
  5.4 Conclusion 74
  5.5 References 75
7 6 Humidity And Light Sensors 77
3383.6 KB
  6.1 Capacitive Humidity And Light Sensor 78
  6.2 PEPC Photocapacitive Detectors 88
  6.3 Organic Phototransistor 101
  6.4 References 114
8 7 Low Temperature Properties Of Organic-Inorganic Ag/P- CuPc/N-GaAs/Ag Photoelectric Senor 119
1852.34 KB
  7.1 Introduction 119
  7.2 Experimental 121
  7.3 Results And Discussion 123
  7.4 Conclusion 140
  7.5 References 143
9 8 Summary & Future Work 145
483.5 KB
  8.1 Future Work 147