The synthesis and optoelectronic properties of biphenyl based conjugated copolymers with varying acceptor units in the polymer backbone were investigated. The well known Donor-Acceptor Theory was used to establish the synthetic pathway for the structural modifications. Solubility issues regarding biphenyl polymer was solved by copolymerizing with soluble units. For this purpose / poly 4-(biphenyl-4-yl)- 4&rsquo / -tert butylspiro[benzo[d]imidazole-2,1&rsquo / -cyclohexane] (P1), poly 4-(biphenyl-4-yl)- 2- dodecyl-2H-benzo[d][1,2,3]triazole (P2) and poly(4-(5-(biphenyl-4-yl)-4-hexylthiophen- 2-yl)-2-dodecyl-7-(4-hexylthiophen-2-yl)-2H-benzo[d][1,2,3]triazole (P3) were synthetized using Suzuki coupling process. Electrochemical properties of these polymers were examined by cyclic voltammetry, spectroelectrochemistry and kinetic studies. Polymers P2 and P3 showed both p- and n-doping behaviors and multicolored electrochromic states. Optical studies revealed that emission color of biphenyl is tuned from blue to orange and the polymers are good candidates for light emitting diode applications. OLED application of P3 was established and outputs of the device were increased by energy transfer studies. The preliminary investigation indicated that P3 possesses promising efficiencies.

AlₓGa₁₋ₓN (x>0.6) based Ultraviolet Light Emitting Diodes (UV LEDs) emit in the UV C range of 200 - 290 nm and suffer from low external quantum efficiencies (EQEs) of less than 3%. This low EQE is representative of a large number of non-radiative recombination events in the multiple quantum well (MQW) layers, which leads to high device temperatures due to self-heating at the device junction. Knowledge of the device temperature is essential to implement and evaluate appropriate thermal management techniques, in order to mitigate optical degradation and lifetime reduction due to thermal overstress. The micro-scale nature of these devices and the presence of large temperature gradients in the multilayered device structure merit the use of several indirect temperature measurement techniques to resolve device temperatures. This work will study UV LEDs with AlₓGa₁₋ₓN active layers, grown on sapphire or AlN growth substrates, and flip-chip mounted onto submounts and package configurations with different thermal properties. Thermal metrology results will be presented for devices with different electrode geometries (i.e., interdigitated and micropixel), for bulk and thinned growth substrates. The body of this work will present a comparative study of optical techniques such as Infrared (IR), micro-Raman and Electroluminescence (EL) spectroscopy for the thermal metrology of UV LEDs. The presence of horizontal and vertical temperature gradients within the device layers will be studied using micro-Raman spectroscopy, while the occurrence of thermal anomalies such as hotspots and shorting paths will be studied using IR spectroscopy. The Forward Voltage (Vf) method, an electrical junction temperature measurement technique, will also be investigated. The Vf method will be applied to the Thermal Resistance Analysis by Induced Transient (TRAIT) procedure, whereby electrical data at short time scales from an operational device will be used to discretize the junction-to- package thermal resistance pathway from the total junction- to-ambient heat path. The TRAIT procedure will be conducted on several LEDs, for comparison. The scope and applicability of each thermal metrology technique will be examined, and the merits and demerits of each technique will be exhibited.

Nanocrystalline silicon (nc-Si:H) is an attractive material for fabrication of low temperature, large area electronic devices due to superior properties versus the traditional amorphous silicon (a-Si:H) and polycrystalline silicon (polySi). Nanocrystalline silicon possess higher carrier mobility and better stability than a-Si:H and better device uniformity and lower fabrication cost than polySi. This thesis looks at the application of nc-Si:H material in fabricating two different diodes used for rectification and light generation. Optimization of n-type nc-Si:H deposited via plasma enhanced vapor chemical deposition (PECVD) was achieved through adjusting the concentration ratio of phosphine (PH3) dopant source gas versus silane (SiH4). Optimizing for dark conductivity, n+ nc-Si:H material with dark conductivity of 25.3 S/cm was deposited using a [PH3]/[SiH4] ratio of 2%. Using the optimized n+ nc-Si:H film, a p-n junction diode utilizing an undoped and an n+ nc-Si:H layers was fabricated designed for rectification use. The diode achieved a current density of 1 A/cm2, an ON/OFF current ratio of 106 and a non-ideality factor of 1.9. When the 200*200µm2 nc-Si:H diodes were employed in a full-wave bridge rectifier, a 2.6 V direct current voltage could be generated from an input sine wave signal with amplitude 2 VRMS and frequency of 13.56 MHz, thus demonstrating the feasibility of using nc-Si:H to fabricate diodes for using on radio frequency identification (RFID) tags. Nanocrystalline silicon was also applied in fabrication of a light emitting diode (LED), by utilizing the nanocrystals embedded inside nc-Si:H, inside which recombination of carriers could result in radiative recombination. By limiting the deposition time of the nc-Si:H, 10 – 20 nm thick films of nc-Si:H were used to fabrication a p-i-n structure LED with average crystallite size between 7.5 nm to 13.7 nm corresponding to an theoretical emission wavelengths in the near infrared region of 875 nm to 963 nm. Unfortunately, light emission from the nc-Si:H LED were not detected using two different methods. Undetectable emission could have been due to a combination of low recombination efficiency due to carriers recombining in defects in the a-Si:H matrix and majority of current travelling completely through the nc-Si:H films without recombining. A study of the thin intrinsic nc-Si:H films used in the LED was carried out. The thin films were found to be highly defected, with large variation in current-voltage relationship measured and hysteresis observed in the IV characteristic. Annealing the nc-Si:H films were found to cause a drop in conductivity explained through hydrogen effusion from the nc-Si:H film during annealing. Passivation of defects was achieved through the use of hydrogen plasma which resulted in a lowering of activation energy measured in the film. Oxygen plasma was also trialed for passivating the nc-Si:H film but the effect was only a temporary increase in current conduction attributed to oxygen ions chemisorbing temporarily at the film surface.

A Laser Music System has been created, that combines a laser and light sensor system with an infrared distance sensing system that detects the position of a user’s hand when it intersects one or more of the individual laser beam. The laser beams, which are made visible by a small amount of smoke in a dark room, provide visual guidance to the user to reduce the difficulty of using a non-contact instrument as well as enhancing an appealing optical effect for the user. The system uses a number of Sharp distance sensors to map the position of the user’s hand to a variable like pitch. The user should move their hand to different heights to achieve a desired pitch. The laser beam should be broken to trigger the desired note.

Despite tremendous achievements, the field of conjugated polymers is still in its infancy, mimicking the more mature inorganic, i.e. silicon-based, technologies. We may though look forward to the realisation of electronic and electrochemical devices with exotic designs and device applications, as our knowledge about the fundamentals of these promising materials grow ever stronger. My own contribution to this development, originating from an idea first put forward by my tutor, Professor Magnus Berggren, is a design for a switchable polymer-based diode. Its architecture is based on a modified version of a recently developed highly-rectifying diode,12 where an intermediate molecular layer has been incorporated in the bottom contact. Due to its unique ability to switch its internal resistance during operation, this thin layer can be used to shift the amount of (forward) current induced into the rectifying structure of the device, and by doing so shift its electrical characteristics between an insulating and a rectifying behaviour (as illustrated below). Such a component should be of great commercial interest in display technologies since it would, at least hypothetically, be able to replace the transistors presently used to address the individual matrix elements. However, although fairly simple in theory, it proved to be quite the challenge to fabricate the device structure. Machinery errors and contact problems aside, several process routes needed to be evaluated and only a small fraction of the batches were successful. In fact, it was not until the very last day that I detected the first indications that the concept might actually work. Hence, several modifications might still be necessary to undertake in order to get the device to work properly.

Nanocrystalline silicon (nc-Si:H) is an attractive material for fabrication of low temperature, large area electronic devices due to superior properties versus the traditional amorphous silicon (a-Si:H) and polycrystalline silicon (polySi). Nanocrystalline silicon possess higher carrier mobility and better stability than a-Si:H and better device uniformity and lower fabrication cost than polySi. This thesis looks at the application of nc-Si:H material in fabricating two different diodes used for rectification and light generation. Optimization of n-type nc-Si:H deposited via plasma enhanced vapor chemical deposition (PECVD) was achieved through adjusting the concentration ratio of phosphine (PH3) dopant source gas versus silane (SiH4). Optimizing for dark conductivity, n+ nc-Si:H material with dark conductivity of 25.3 S/cm was deposited using a [PH3]/[SiH4] ratio of 2%. Using the optimized n+ nc-Si:H film, a p-n junction diode utilizing an undoped and an n+ nc-Si:H layers was fabricated designed for rectification use. The diode achieved a current density of 1 A/cm2, an ON/OFF current ratio of 106 and a non-ideality factor of 1.9. When the 200*200µm2 nc-Si:H diodes were employed in a full-wave bridge rectifier, a 2.6 V direct current voltage could be generated from an input sine wave signal with amplitude 2 VRMS and frequency of 13.56 MHz, thus demonstrating the feasibility of using nc-Si:H to fabricate diodes for using on radio frequency identification (RFID) tags. Nanocrystalline silicon was also applied in fabrication of a light emitting diode (LED), by utilizing the nanocrystals embedded inside nc-Si:H, inside which recombination of carriers could result in radiative recombination. By limiting the deposition time of the nc-Si:H, 10 – 20 nm thick films of nc-Si:H were used to fabrication a p-i-n structure LED with average crystallite size between 7.5 nm to 13.7 nm corresponding to an theoretical emission wavelengths in the near infrared region of 875 nm to 963 nm. Unfortunately, light emission from the nc-Si:H LED were not detected using two different methods. Undetectable emission could have been due to a combination of low recombination efficiency due to carriers recombining in defects in the a-Si:H matrix and majority of current travelling completely through the nc-Si:H films without recombining. A study of the thin intrinsic nc-Si:H films used in the LED was carried out. The thin films were found to be highly defected, with large variation in current-voltage relationship measured and hysteresis observed in the IV characteristic. Annealing the nc-Si:H films were found to cause a drop in conductivity explained through hydrogen effusion from the nc-Si:H film during annealing. Passivation of defects was achieved through the use of hydrogen plasma which resulted in a lowering of activation energy measured in the film. Oxygen plasma was also trialed for passivating the nc-Si:H film but the effect was only a temporary increase in current conduction attributed to oxygen ions chemisorbing temporarily at the film surface.

The field of organic electronics is recently emerging in modern electrical applications. Organic light emitting diodes have been developed and are implemented in commercially available products. The novel materials are also used in sensor applications, utilizing their intrinsic physical, chemical and electrical characteristics. Poly(3,4-ethylenedioxythiophene): poly(styrene-sulfonic acid) (PEDOT:PSS) is one of the most successful organic conductive materials. Developed as antistatic coating, it is now used in other fields as well such as in electro-optical devices as transparent electrodes. One of the reasons for its widely spread use is that water-based dispersions in high quality are available. In addition, it is considered highly stable, resisting degradation under typical ambient conditions. For this work, the usability of PEDOT:PSS as active layer for electromechanical sensor applications was investigated. The electrical properties of the material were characterized including temperature dependencies and environmental influences. A piezoresistive effect with negative sign was found. It is small in magnitude and of the same order as the change in resistance due to geometrical effects. The piezoresistive effect is temperature dependent and increasing in magnitude with higher temperatures. An average longitudinal piezoresistive coefficient pi_l of -5.6x10-10 Pa-1 at room temperature has been evaluated. The transverse effect under the same conditions is opposite in sign and two thirds in magnitude of the lateral effect. The hole mobility of PEDOT:PSS follows an Arrhenius function and thus the resistivity has a negative temperature coefficient. Some other thermally induced effects have been observed such as de-doping of the material resulting in an irreversibly lowered conductivity. Due to the low thermal conductivity of the substrate material used, Joule heating of the samples played an important role during the characterization and was utilized to investigate the temperature dependencies. The change of resistance caused by an applied stress to the sample is small, with a gage factor smaller than one.

The use of polymers in electro-optical devices, especially light-emitting diodes (OLEDs), has become very popular in recent years, due to their ease of processability. The major drawback of using polymers in these systems is their time-consuming synthesis when trying to improve upon their physical properties. For example, each time a new color or better conducting properties are desired, a new monomer must be synthesized. To circumvent these problems, the system described in this work is designed to connect the well-known chromophore aluminum tris(8-hydroxyquinoline) (Alq3) to a norbornene monomer unit, followed by polymerization using ring-opening metathesis polymerization (ROMP), thus allowing for the processability of a polymer while maintaining the fluorescent properties of the metalloquinolate. The benefit of this system is that the monomers can be easily altered in order to tune color emission or to enhance the polymer properties. Some of the alterations include changing the metal center from aluminum to zinc in order to improve electron injection, adding substituents to the 8-hydroxyquinoline ligand in order to tune the emission color, and copolymerizing the Alq3-monomer with other norbornene monomers containing either a hole- or an electron-transport material side-chain to improve conductivity. These alterations lead to improved device performance and, more importantly, to a new method of designing polymeric systems for use in electronic devices.

It is the objective of this work to focus on heat dissipation in gallium nitride based solid-state logic devices as well as optoelectronic devices, a major technical challenge. With a direct band gap that is tunable through alloying between 0.7-3.8 eV, this material provides an enabling technology for power generation, telecommunications, power electronics, and advanced lighting sources. Previously, advances in these areas were limited by the availability of high quality material and growth methods, resulting in high dislocation densities and impurities. Within the last 40 years improvements in epitaxial growth methods such as lateral epitaxial overgrowth (LEO), hydride vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), and metal organic chemical vapor deposition (MOCVD), has enabled electron mobilities greater than 1600 cm2V/s, with dislocation densities less than 109/cm2. Increases in device performance with improved materials have now been associated with an increase in power dissipation (>1kW/cm2) that is limiting further development. In the following work thermophysical material of III-V semiconducting thin films and associated substrates are presented. Numerical modeling coupled with optical (micro-IR imaging and micro-Raman Spectroscopy) methods was utilized in order to study the heat carrier motion and the temperature distribution in an operating device. Results from temperature mapping experiments led to an analysis for design of next generation advancements in electronics packaging.

In the study, conductive distributed Bragg reflectors (DBRs) fabricated at room temperature based on porous indium tin oxide (ITO) on dense ITO bilayers were proposed for resonant cavity organic light emitting diodes (RCOLEDs). In the fabrication of the ITO DBRs, the low refractive index porous ITO films were obtained by applying supercritical CO2 treatment at different temperature and pressures on the spin-coated sol-gel ITO films. On the other hand, the high refractive index ITO films were grown at room temperature by long-throw reactive ratio-frequency magnetron sputtering. The refractive index of the porous ITO film and ITO films were 1.54 and 2.0, respectively. For the DBR with 4 pairs ITO bilayers, the optical reflectance of more than 70 % was achieved. The stop band and the average resistivity is 140 nm and 2.2¡Ñ10-3 £[-cm, respectively. Finally, electrical and optical characteristics of the RCOLEDs fabricated on the ITO DBR were investigated and compared with those of the conventional OLEDs. The maximum luminous efficiency of 3.79 cd/A was obtained at 347 mA/cm2 for the RCOLED. This luminous efficiency was 26 % higher than that of the conventional OLED.