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We report an ultralow power consuming and forming-free hybrid flexible resistive random access memory device fabricated with poly(4-vinylphenol) (PVP):MoS2 composite and HfO x bilayer, exhibiting threshold switching with ultralow ON-current of 500 nA. While the higher concentration of MoS2 imparted the higher leakage current in the devices, the lower concentration devices exhibited decent switching with set and reset powers as low as 270 and 0.1 nW, respectively. The ultralow switching current indicates the formation of multiple weak nanosized conductive filaments created due to electromigration of Ag atoms under external bias. Moreover, heating temperature-dependent study of switching behavior confirms the metallic nature of the filament as the low resistance state (LRS) current falls significantly with rising temperature. Furthermore, these devices exhibited remarkable mechanical strength on flexible substrate with demonstration of nondestructive switching characteristics at a bending radius as low as 2.5 mm and after 100 consecutive compressive and tensile strain cycles at ±5-mm radius. The ultralow switching current with high flexibility indicates the capability of devices for advancement toward future low-power flexible memories and computing systems.

Resistive switching behavior of poly (4-vinylphenol):graphene oxide (PVP:GO) composite and ultrathin HfO x hybrid bilayer was explored for developing high-performance flexible resistive random access memory (RRAM) devices. These devices, fabricated with a PVP:GO equivolume solution spin-coated and atomic layer deposited ultrathin HfO x as an active bilayer, exhibited excellent bipolar switching behavior with set and reset voltages as low as 0.6 and −1.46 V, ${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ of >105, and ac and dc switching endurance of over 1400 and 800 cycles, respectively. The same device configuration realized over a flexible polyethylene terephthalate (PET) substrate exhibited a memory window of >103 even after undergoing large mechanical strain (correspoding to a 5-mm bending radius). In addition, after 150 cumulative cycles of consecutive tensile and compressive strain at a 5-mm bending radius, flexible RRAMs demonstrated a clear memory window of $4\times 10^{{3}}$ for 104 s. Overall, the incorporation of GO into the PVP solution resulted in achieving better control over conductive filament (CF) growth and, therefore, improved repeatability and reliability. This article indicates that the strategy of incorporating composite and organic–inorganic active bilayer can lead toward the development of high-performance flexible RRAMs.

Organic FETs (OFETs) with bilayer dielectric poly(4-vinylphenol) (PVP)/HfO2 and polyvinyl alcohol (PVA)/HfO2 were fabricated on a flexible low-cost Kapton tape substrate with TIPS -pentacene:polystyrene as an active layer. The devices exhibited average and maximum field-induced mobility of 0.25(±0.10) and 0.37 cm $^{{{2}}}\text{V}^{{-{1}}}\,\,\text{s}^{{-{1}}}$ for PVP/HfO2 devices, and 0.35(±0.18) and 0.69 cm $^{{{2}}}\text{V}^{{-{1}}}\,\,\text{s}^{{-{1}}}$ for PVA/HfO2 devices, respectively, with low threshold voltage and ${I}_{ \mathrm{\scriptscriptstyle ON}}$ to ${I}_{ \mathrm{\scriptscriptstyle OFF}}$ ratio approaching $10^{{{4}}}$ for both types of devices. Overlapping transfer multiple scans with very less performance variation under ambient conditions were observed. The devices were found to be fairly stable even when electrical stress was applied after a period of 5 months. Devices exhibited small degradation in ${I} _{{\text {DS}}}$ and small $\Delta {V} _{{\text {TH}}}$ with high degree of reliability and small performance spreads under combined effects of ambient exposure over a period of 5 months and successive electrical stress. In addition, inverter based on these OFETs with external load was also demonstrated.

In this work, a combination of a thin layer of Copper (II) phthalocyanine (CuPc) and TIPS-pentacene crystal was used to enhance the photo-sensing spectrum of photo- sensitive organic field-effect transistors (photo-OFETs). In TIPS-pentacene/CuPc bi-layer devices, the different conduction path not only reduced the total number of traps but also enhanced the sensing spectrum. It was found that, though the TIPS-pentacene was able to sense only blue and green colour well, and CuPc was able to sense only red and green colour well; the TIPS-pentacene/CuPc bi-layer were able to sense all three colors, enhancing the range of sensing. On illumination, bi-layer TIPS-pentacene/CuPc OFETs exhibited higher values of shift in threshold voltage (|ΔVTH|) compared to neat TIPS-pentacene and bare CuPc OFETs, due to change in the spatial distribution in the trap state density and associated pattern of trapping of photo-generated charge carriers. It was also found that the values of photo-responsivity (Rmax) and photo-detection time for the bi-layer OFETs were in between that for OFETs with TIPS-pentacene or CuPc.

Performance of symmetric lateral doping-free bipolar junction transistor (BJT) on silicon on insulator (SOI) in universal gates and ring oscillator were investigated. Charge carriers in SOI at emitter and collector regions are induced with two unique approaches, i.e., the charge plasma (CP) and polarity control (PC). Four types of devices (CP-NPN, CP-PNP, PC-NPN, and PC-PNP) was used for bipolar CMOS type NAND and NOR gates. Excellent transient response with rise and fall time less than 5 ns and propagation delay less than 2.4 ns were obtained.

In part I of this paper, we developed physical insights into the role and impact of acceptor and donor traps—resulting from C-doping in GaN buffer—on avalanche breakdown in AlGaN/GaN HEMT devices. It was found that the donor traps are mandatory to explain the breakdown voltage improvement. In this paper, silicon doping is proposed and explored as an alternative to independently engineer donor trap concentration and profile. Keeping in mind the acceptor and donor trap relative concentration requirement for achieving higher breakdown buffer, as depicted in part I of this paper, silicon & carbon codoping of GaN buffer is proposed and explored in this paper. The proposed improvement in breakdown voltage is supported by physical insight into the avalanche phenomena and role of acceptor/donor traps. GaN buffer design parameters and their impact on breakdown voltage as well as leakage current are presented. Finally, a modified Si-doping profile in the GaN buffer is proposed to lower the C-doping concentration near GaN channel to mitigate the adverse effects of acceptor traps in GaN buffer.

Hybrid CBRAM devices based on PVP/HfOx bilayer were investigated for their switching performance. A reliable and low voltage bipolar resistive switching operation was observed in these devices with repeatability of 300 cycles, Ion/Ioff of 80, set (Vset) and reset (Vreset) voltages of 1.03 V and −0.68 V, retention time of 7200 s, and switching endurance of >2000 cycles in devices with 2.5 wt% PVP concentration. Low device-to-device variation was observed with 10 devices tested showing nearly similar switching parameters. Weibull's distribution of Vset and Vreset voltages have indicated reliable switching performance in devices. The pinholes formation in PVP layer guides the confined growth and dissolution of Ag conductive filament (CF) in the bilayer structure resulting in a stable, reliable and low voltage switching operation. PVP film roughness and pinholes depth have shown downtrend with PVP concentration. During the set process, a CF formed across the electrodes constitutes of Ag atoms, due to pinholes assisted electro-migration of Ag ions. Whereas in the reset process, the diffused Ag+ ions migrate back towards top electrode due to the electrochemical and joule-heating assisted rupture of CF in the PVP/HfOx bilayer structure.

BiFeO3 thin films are deposited on FTO coated glass substrates using a simple sol-gel deposition technique, limiting thickness about 70 nm and Ag/BiFeO3/FTO RRAM devices are prepared. The devices showed low-voltage bipolar switching with the maximum Ion/Ioff ~ 450, and low set and reset voltages ~ 1.1 V and -1.5 V, respectively. The devices are stable against on-off cycles with ~ 104 s retention time without any significant degradation. The variations in the set and reset voltages are 0.4 V and 0.6 V, respectively. We found that ohmic and trap-controlled space charge limited conductions are responsible for low and high resistance states, respectively. The resistive switching mechanism is attributed to the formation and rupturing of the metal filament during the oxidation and reduction of Ag ions for the set and reset states., 15 Pages, 4 Figures, Submitted for publication in Journal of American Ceramic Society

The critical role of the mixing ratio of the semiconductor and polymer solutions on the performance and electro-mechanical stability of the flexible blend OFETs is investigated. An improvement in the OFET performance was observed with increasing fraction of polymer in the solution. The maximum field-effect mobility improved from 0.08 for neat TIPS-pentacene OFETs to 0.24, 0.25 and 0.57 cm2 V−1 s−1 for semiconductor:polymer blend OFETs with mixing ratio of 3:1, 1:1 and 1:3 respectively. Under stress conditions of VDS = VGS = −5 V for 1 h, the 1:3 blend devices outperformed other categories of devices with very small drain current decay of ∼2% and 11% and small threshold voltage shift of 0.05 V and 0.27 V before and after 1.27% (Rbend = 5 mm) tensile strain application respectively. These devices also exhibited superior reliability with least performance spread over 100 continuous transfer characteristics measurement cycles before and after application of strain.

Atomic layer deposited AlO x based resistive random access memories were fabricated with a new multi-temperature deposition (MTD) scheme, where a 40 nm thick AlO x film was deposited with temperature-thickness sequence of 150 °C (10 nm)/80 °C (20 nm)/150 °C (10 nm). Electrical characteristics of thus fabricated devices demonstrate improved bipolar resistive switching behavior with lower set and reset voltages of 0.65 V and − 1.15 V respectively, decent repeatability of 75 cycles, reliable data retention upto 10 3 s, small variation of 0.29 V and 0.17 V in set and reset voltages respectively, and symmetric current-voltage curves. The conduction mechanism has been explained as ohmic and space charge limited conduction at lower and higher voltages respectively. Due to different deposition temperature, oxygen vacancy concentration was different in each layer of the MTD film, which led to formation of a conductive filament with nonhomogeneous strength and dimensions across the film. Localization of effective switching phenomenon in the region with weaker conductive filament yielded an improved performance with lower switching voltages in corresponding multi-temperature devices.

Effect of ultra-violet (UV) irradiation (λpeak = 365 nm) on the electrical characteristics of solution processed flexible TIPS-pentacene organic field-effect transistors (OFETs) has been investigated. Pristine TIPS-pentacene OFETs demonstrated average field-effect mobility of 0.1 cm2 V−1 s−1, with near zero threshold voltage and current on-off ratio of ∼104. On UV irradiation, OFETs displayed a joint photoconductive and photovoltaic effect due to photo-generated excitons. The maximum current modulation and photo-responsivity obtained from these OFETs were ∼500 and ∼43 mA/W respectively at an intensity of 1.8 mW/cm2 while operating at a low voltage of −5 V. On increasing the irradiation time, a positive shift in the threshold voltage was observed. At larger values of irradiation time, a roll-off in maximum drain current and mobility values were observed, which was attributed to slight deterioration in crystallinity due to prolonged UV exposure, as confirmed from X-ray diffraction studies. Similar trend was observed for mobility and threshold voltage values, when gate bias during UV irradiation was increased. In addition, transistors exhibited a repeatable dynamic response to periodic pulses of UV irradiation.

Photo-response of solution processed flexible TIPS-pentacene organic field-effect transistors is evaluated under illumination with visible light of red, green, and blue colors having minimum wavelengths of 620, 520, and 460 nm. For −10 V operation, pristine photo-OFETs exhibited average field-effect mobility of 0.11 cm $^{2}\text{V}^{-1}\text{s}^{-1}$ , near zero threshold voltage, and current ON–OFF ratio of ~105. These photo-OFETs exhibited prevalent photovoltaic characteristics with shift in the threshold voltage upon illumination, which was found to increase with rising intensity, illumination time, and gate bias during illumination. For low-voltage operation at −5 V, maximum current modulation of $4\times 10^{4}$ and 102, and photo-responsivity of 17 mA/W and 35 mA/W, respectively, were achieved for blue (intensity of 1.7 mW/cm2) and green (intensity of 0.4 mW/cm2) light illuminations. However, these photo-OFETs did not show significant response to red light. A fast dynamic response to periodic pulses of illumination was also observed. For a gate bias of +10 V and illumination time of 500 s, maximum current modulation of 105 was achieved for blue light illumination.

BiFe 0.99 Cr 0.01 O 3 thin film is deposited on FTO glass using sol-gel technique. The deposited film is used in Ag/ BiFe 0.99 Cr 0.01 O 3 /FTO configuration to understand its potential as RRAM device. The device showed forming free bipolar RRAM characteristics with Ion/Ioff~80. The device showed non-volatile behaviour by maintaining its LRS and HRS states for 104 s. The device exhibits excellent reproducibility up to 100 cycles and reliability of V set and V reset voltage is observed. The endurance characteristics for 200 cycles ensures the stability of the device, further, conduction mechanism is attributed to filament formation and switching mechanism is assigned to migration of silver ion inside the film.

In this work, we have explored the effect of TIPSpentacene: polystyrene (PS) blend on electrical performance and photo-response of solution processed organic field-effect transistors (OFETs). It was observed that though the blend OFETs show better electrical performance, the photo-responsivity (R) of neat TIPS-pentacene OFETs was significantly better. This study was performed for different color lights such as blue, red, and green, as well as for ultraviolet light (UV). R was highest for blue color (~2600 mA/W for neat, ~230 mA/W for blend), and smaller for other cases. Low R value in blend devices is attributed to less trapping of photo-generated charge carriers during photo-illumination compared to their neat counterparts.

High-performance operationally stable organic field-effect transistors were successfully fabricated on a PowerCoat HD 230 paper substrate with a TIPS-pentacene:polystyrene blend as the active layer and poly(4-vinylphenol)/HfO2 as the hybrid gate dielectric. The fabricated devices exhibited excellent p-channel characteristics with a maximum and av field effect mobility of 0.44 and 0.22(±0.11) cm2 V–1 s–1, respectively, av threshold voltage of 0.021(±0.63) V, and current on–off ratio of ∼105 while operating at −10 V. These devices exhibited remarkable stability under effects of gate bias stress and large number of repeated transfer scans with negligible performance spread. In addition, these devices displayed very stable electrical characteristics after long exposure periods to humidity and an excellent shelf life of more than 6 months in ambient environment. Thermal stress at high temperatures however deteriorates the device characteristics because of the generation and propagation of cracks in the active ...

In this report, we have demonstrated the optical non-volatile memory characteristics using CuPc OFET. The memory operation was comprehensively demonstrated with different programming conditions. It was found that the programming of CuPc OFET with an electric pulse at the gate terminal under UV-light photo-illumination compared to other programming conditions, could substantially increase the memory window due to massive charge trapping in the polymer electret layer, which causes shift in the device transfer characteristics from low-conduction state (“OFF state”, or logic 0) to high conduction state (“ON state”, or logic 1) at VGS = 0V. From device operation at −50V, a memory window of greater than 45V could be achieved by applying a programming voltage of +70 V at the gate terminal under UV-light photo-illumination. Moreover, it was completely erased by applying −100 V at the gate terminal in dark.

Logic gates are designed using symmetric lateral doping-free bipolar junction transistor (BJT) on silicon on insulator (SOI) using differential pass transistor logic, and their performance matrices are presented. Charge carriers are induced in lightly doped emitter and collector regions using two unique approaches. i.e., the charge plasma (CP) and polarity control (PC). AND, OR and XOR gates are designed using four types of devices (CP-NPN, CP-PNP, PC-NPN, and PC-PNP) and transient and noise margin analysis are performed. The transient response shows rise and fall time less than 100 ps while worst-case noise margin of 0.25 V observed for an input voltage of 1 V. Moreover, 2:1 multiplexer is also designed and explored for output transient and voltage levels. The delay of less than 2.2 ns is achieved with a nominal deviation of 0.1 V and 0.04 V for high and low output levels respectively.

The crucial role of molecular weight of the polymer dielectric in regulating the electrical performance and photo-response of TIPS-pentacene OFETs has been explored using poly(vinyl alcohol) (PVA) as the polymer dielectric layer. With increasing molecular weight of PVA, a degradation in the electrical and photo-response was observed. Atomic-force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR) and X-ray Diffraction (XRD) studies revealed that with increase in PVA molecular weight, polarizability of PVA dielectric layer and thus strength of the OFET channel reduced due to decreased hydroxyl group concentration oriented perpendicular to the PVA-semiconductor interface. Further, due to rising surface roughness of underlying PVA film with its molecular weight, macroscopic irregularities and therefore trap density in the active layer grown over it also increases. Therefore, both of these molecular weight dependent factors influence overall device performance and photo-response of OFETs in a critical way.

This paper for the first time presents a comprehensive computational modeling approach for AlGaN/GaN high electron mobility transistors. Impact of the polarization charge at different material interfaces on the energy band profile as well as parasitic charge across the epitaxial stack is modeled and studied. Furthermore, impact of surface and bulk traps on two-dimensional electron gas, device characteristics, and gate leakage is accounted in this paper. For the first time, surface states modeled as donor type traps were correlated with gate leakage. Moreover, a new approach to accurately model the forward gate leakage in Schottky gate devices is proposed. Finally, impact of lattice and carrier heating is studied, while highlighting the relevance of carrier heating, lattice heating, and bulk traps over the device characteristics. In addition to this, modeling strategy for other critical aspects like parasitic charges, quantum effects, S/D Schottky contacts, and high field effects is presented.

Phase separation induced high carrier mobility and electrical stability are achieved in organic field-effect transistors using TIPS-pentacene:polystyrene blends. Rigid Si/SiO 2 substrate was especially chosen to explore the phase separation. A vertical phase separation between TIPS-pentacene and polystyrene as confirmed from scanning electron microscopic image, evetually leads to excellent carrier mobility in polymer blend devices compared to that of neat TIPS-pentacene. Maximum hole mobility improved from 0.2 cm 2 V −1 s −1 for neat TIPS-pentacene on SiO 2 to 2.6 cm 2 V −1 s −1 for TIPS-pentacene blends with PS, with average value of 1.5 cm 2 V −1 s −1 . Apart from higher mobility, TIPS-pentacene:PS blend devices also showed much lower decay in drain current (∼30%) during a constant bias-stress of 2 h, compared to neat devices (∼80%). Interestingly, This decay was fully recovered for blend devices under rest conditions. The corresponding shift in the threshold voltage due to bias-stress was lower for TIPS-pentacene:PS device due to better quality of interface as confirmed by lower values of density of interface traps and higher trapping time. High electrical stability in TIPS-pentacene:polystyrene blend devices was also supported by repeatabiliiy studies, which exhibited nearly unchanged device characteristics.

High-performance solution processed flexible organic field-effect transistors with 6,13(bis-triisopropylsily-lethynyl) pentacene and polystyrene blend are demonstrated with high electro-mechanical stability. For −5 V operation, field-effect mobility up to 1.1 cm $^{2}~\text{V}^{\mathrm {-1}}~\text{s}^{\mathrm {-1}}$ and threshold voltage as low as −0.1 V were obtained with high current on–off ratios of $\sim 10^{5}$ due to high quality dielectric–semiconductor interface developed during solvent evaporation. Stable electrical characteristics were achieved with increasing duration of mechanical strain, and after multiple cycles of tensile and compressive strain. Drain current decay of 10%, very large trapping time of $\sim 10^{8}$ s, and a very small threshold voltage shift of 0.3 V were observed during bias stress of 1 h, signifying low charge carrier trapping and a high quality of dielectric–semiconductor interface, which was retained largely after two days of continuous tensile strain. Moreover, after 100 cycles of tensile and compressive strain, the corresponding shift in threshold voltage due to bias stress was still $\sim 0.5$ V. Overall, a high performance and stability were demonstrated under collective effects of mechanical and electrical stress.

A computationally efficient analytical model to accurately predict the electrical characteristics of wrap-gate carbon nanotube FETs (CNTFETs) is proposed and described in this paper. A wrap-gate structure offers an ideal geometry with minimum body thickness and maximum control over the channel as well as improved device scalability. The parasitic effects present in a real device are incorporated into an ideal wrap-gate device model, and the Poisson–Schrodinger equations are solved self-consistently to obtain the potential and carrier density at the top of the barrier. Exact analytical expressions, such as CNTFET density-of-states are used for approximately evaluating the integral expressions. Finally, the drain current is obtained for near-ballistic transport in the device. The electrical characteristics from our model are validated with recently reported experimental results from the literature, demonstrating good accuracy when the device is on. The subthreshold characteristics are underestimated and offer scope for improvement. Various performance metrics, including threshold voltage and subthreshold swing, and on-current are within 2–11% error. The proposed model can thus be used to study the performance of wrap-gate CNTFETs under various parametric conditions, and extended to circuit simulation models, such as SPICE.

Flexible organic field-effect transistors (OFETs) with TIPS-pentacene: polystyrene (PS) blend are demonstrated to exhibit enhanced mobility and significantly improved electrical stability compared to neat TIPS-pentacene on poly(4-vinylphenol) (PVP) dielectric (bi-layer OFETs), along with high mechanical stability. Due to merit of high quality dielectric-semiconductor interface, pristine TIPS-pentacene: PS blend OFETs exhibited maximum mobility of 0.93 cm2 V−1 s−1 with average of 0.44(±0.25) cm2 V−1 s−1 compared to 0.14(±0.10) cm2 V−1 s−1 for bi-layer OFETs with high current on-off ratios on the order 105 for both. Both types of devices exhibited high electrical stability upon bending with increasing magnitude of strain or its duration up to 5 days. However, significant differences in electrical stability of devices were observed upon applying constant bias-stress for 40 min to 1 h. Pristine blend devices exhibited outstanding electrical stability with very low drain current decay of

The effect of structural dissimilarity of the additive solvent from the main solvent on the properties of the solution and resulting crystals for solution processed organic field-effect transistors (OFETs) is comprehensively studied. Organic semiconductor TIPS-Pentacene was explored with toluene as the main solvent and benzene, cyclohexane, and hexane as additives for making semiconductor solutions. The solution formation with various solvents is explained by Hansen’s solubility theory, according to which the binary solvent with higher structural dissimilarity between constituent solvents is a weaker solvent of the organic semiconductor; which eventually supports better molecular aggregation and crystallinity in the resulting crystallites. As investigated by XRD, the degree of crystalline order systematically increased with rising dissimilarity in component solvents; integrated intensity ratio rising from 0.52 for toluene to 0.54, 0.69 and 0.72 respectively for toluene/benzene, toluene/cyclohexane, and toluene/hexane. The variation in degree of crystallinity is also reflected in electrical properties of OFETs, where the field-effect mobility improved from 0.05 cm2/(V.s) for toluene solvent to higher than 0.1 cm2/(V.s) for toluene/hexane.

Flexible organic field-effect transistors with high electrical stability upon bending are demonstrated on indium tin oxide coated polyethylene terephthalate substrates with TIPS-Pentacene semiconductor crystals formed by drop casting on a hybrid gate dielectric consisting hafnium dioxide grown by atomic layer deposition and spin coated poly(4-vinylphenol). Fabricated devices exhibited excellent p-channel characteristics with field-effect mobility up to 0.12 cm2/Vs with high current on/off ratio >104 and low threshold voltage of −0.2 V. Device performance was slightly affected by mechanical strain applied by bending for 5 min with radius varying from 12.5 mm to as low as 5.0 mm; and a high stability in performance was demonstrated upon applying constant tensile strain for more than 48 h at bending radius of 5.0 mm. It was found that strain induced changes in the device performance primarily occur due to increase in dielectric surface roughness; and the semiconductor-dielectric interface uniformity is influenced more with magnitude of strain rather than its duration.

BiFeO3 based resistive random access memory (RRAM) devices are fabricated using a low-cost solution process to study the effect of an Al top electrode on switching behavior and reliability. Fabricated devices demonstrated bipolar switching characteristics with a moderate Ion/Ioff ratio, set and reset voltages of ∼−1.3 V and ∼0.8 V, DC and AC endurance of more than 250 cycles and 7100 cycles, respectively, and a retention time of over 104 s, confirming the non-volatile resistive switching behavior. The ohmic and trap filled space charge limited conduction dominates the conduction mechanism in the devices at lower and higher voltages, respectively. Moreover, impedance spectroscopy measurements substantiate the presence of an AlOx layer at the Al/BiFeO3 interface resulting from the Al–O interaction at the junction, which is the possible rationale of reliable complementary switching in these RRAM devices. The switching mechanism is elucidated using the formation and rupture of the oxygen vacancy mediated filament, assisted by the participation of a thin AlOx layer at the Al/BFO interface. The role of the thin AlOx layer is explained by modeling of impedances.

In this work, a TCAD based approach is presented to model electrical behavior of TIPS-Pentacene: polymer blend organic field-effect transistors (OFETs). Stress induced and temperature induced effects are also captured, thereby accurately modeling the device behavior under different operating conditions. The framework is validated against experimental results and is then used to estimate the effect of temperature on characteristics of inverter circuit using this device.

Effect of thermal annealing on the performance of flexible OFETs was investigated. Annealing at low temperatures up to 50 °C enhanced the molecular ordering and granular arrangement leading to improved device performance, however, a permanent degradation was induced at high temperature annealing due to loss in crystallinity and crack generation. An annealed device exhibited a larger decay in drain current than a pristine device under constant bias stress. Under combined effects of mechanical and thermal stress, effect of thermal stress was found to be dominant at higher annealing temperatures, resulting in monotonic performance degradation.

For the very first time, influence of traps on avalanche breakdown of AlGaN/GaN HEMTs is discussed. Impact of surface and bulk traps on breakdown voltage and device scaling is discussed with associated physics. Surface trap's were found to cause distinct breakdown characteristics with breakdown point varying from gate edge to drain edge, depending on nature, type and concentration. Buffer traps too influence the electric field near gate edge and leakage through the device, thereby affecting breakdown voltage accordingly.

A unified approach of directional solvent vapor annealing for crystal alignment in solution-processed organic semiconductors is proposed. Highly crystalline molecular self-assembly of the drop-cast technique is further enhanced by postprocessing scheme of the solvent vapor annealing with additional benefit of alignment of the crystalline domains. In this technique, a mixture of carrier gas and solvent vapors are made to flow in a certain direction and in the close proximity of the surface of the substrates carrying the solution. Flow of the carrier gas imparts directionality to the semiconducting crystalline ribbons, whereas the influx of the solvent vapors improves the crystalline order in the semiconducting film. The flow rate of the carrier gas and the position of the substrate in the interaction chamber are the primary regulating factors, which have the ability to provide a semiconducting layer with a well-aligned and interconnected assembly of long ribbons. These favorable film properties further materialize in the form of electrical performance of the corresponding field-effect transistors. The versatility of this technique makes it a viable alternative for the solution processing of organic semiconductors.

Organic field effect transistors (OFETs) have been widely explored for their popular applications in flat panel displays and various kinds of affordable sensors. The overall performance of the device depends on the quality of semiconductor-dielectric interface, and degree of crystalline order in the active layer, close to the above said interface. In the special league of solution processed OFETs, semicondutor: polymer blends have been reported as one of the best possible ways to achieve an intimate, uniform and defect free semiconductor-dielectric interface in a single step. In addition, degree of crystalline order can be further ameliorated through solvent vapor annealing (SVA), which essentially controls the evaporation time of the solvent.

A systematic and comprehensive study on the charge-carrier injection and trapping behavior was performed using displacement current measurements in long-channel capacitors based on four promising small-molecule organic semiconductors (pentacene, DNTT, C10-DNTT and DPh-DNTT). In thin-film transistors, these semiconductors showed charge-carrier mobilities ranging from 1.0 to 7.8 cm2 V−1 s−1. The number of charges injected into and extracted from the semiconductor and the density of charges trapped in the device during each measurement were calculated from the displacement current characteristics and it was found that the density of trapped charges is very similar in all devices and of the order 1012 cm−2, despite the fact that the four semiconductors show significantly different charge-carrier mobilities. The choice of the contact metal (Au, Ag, Cu, Pd) was also found to have no significant effect on the trapping behavior.