Meghan P. Patankar

Broadband parametric amplification with impedance engineering: Beyond the gain-bandwidth product

We present an impedance engineered Josephson parametric amplifier capable of providing bandwidth beyond the traditional gain-bandwidth product. We achieve this by introducing a positive linear slope in the imaginary component of the input impedance seen by the Josephson oscillator using a

Bulk and contact-sensitized photocarrier generation in single layer organic devices

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Photoconduction in Alq3

transformer. Our theoretical model predicts an extremely flat gain profile with a bandwidth enhancement proportional to the square root of amplitude gain. We experimentally demonstrate a nearly flat 20 dB gain over a 640 MHz band, along with a mean 1-dB compression point of -110 dBm and near quantum-limited noise. The results are in good agreement with our theoretical model.

Modified CVD deposition of poly(p-phenylene vinylene)

In this paper, we report on the photoelectronic properties of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD) studied in sandwich geometry. In particular, we have obtained from both forward and reverse bias measurements the μτ product for holes in TPD. μ is the hole mobility and τ is the carrier trapping time. The μτ product is a measure of the electronic quality of the material and allows a quantitative comparison of different samples. We have carried out numerical simulations to understand the photocurrent in these structures. We show that in reverse bias, the photocurrent (PC) is due to carrier generation in the bulk of the sample. The carrier generation is governed by field assisted exciton dissociation at electric fields greater than 106V∕cm. At lower fields the generation of carriers occurs spontaneously in the bulk of the sample. In forward bias, the photocurrent is due to exciton dissociation at the indium tin oxide contact. We also obtain a μτ product for holes from forw...

Study of electrical transport of hole-doped TPD

Photoelectronic properties of Alq3 were studied by photoconductivity (PC) measurements in thin film, sandwich (indium-tin-oxide/Alq3∕LiF∕Al) devices. We find that the photocurrent is dominated by bulk generation of carriers for incident photon energies greater than 2.75eV. The quantum efficiency of photocarrier generation has been measured from carrier collection measurements to be about 10%. The quantum efficiency is largely independent of electric field. This enables a direct measurement of the electric field dependence of mobility using photoconductivity measurements, which is used for quantitative analysis of the dark forward current in these devices. PC measurements were also used to obtain (μ0nτn) product which can be used as a measure of material quality. For Alq3, we find that the value of (μ0nτn) product was between 3×10−15cm2∕V to 8×10−15cm2∕V for different samples. In forward bias, at high field the photocurrent shows saturation accompanied by a phase shift. These effects are attributed to spac...

Electronic transport in doped pyrenyl carbazole

In this paper we report on the room temperature polymerization of poly(p-phenylene vinylene) (PPV) using UV light in a CVD process. The main advantage of this process is that it is possible to deposit PPV on low cost plastic substrates and enables roll-to-roll processing in a manufacturing process. The scheme reported in this paper raises the possibility of bringing together two different technologies-polymers and small molecules-in a single roll-to-roll manufacturing process for organic semiconductors.

Spontaneous and field induced photocarrier generation in TPD and its blend

In this paper we study the electrical properties of hole-doped TPD using C-V and I-V-T measurements. F4- TCNQ is the acceptor molecule used to dope TPD. From C- V measurements the Fermi level of the system is determined to be at 0.15 eV with respect to the HOMO of TPD. The activation energy of the hole mobility is found from temperature dependence of the ohmic dark current.

Red shifted electroluminescence in OLEDs using organic alloy of hole transport materials

In this paper, we report on electronic transport and impedance measurements on thin films of unintentionally hole doped 3,6-dipyrenyl-N-hexylcarbazole. Evidence for doping from dc conductivity, ESR, and capacitance measurements is presented. From a study of the bias, temperature and frequency dependence of capacitance, we estimate the integrated density of states above the Fermi level to be 1017/cm3. This is also the doping concentration in these samples.

Synthesis and characterisation of soluble aluminium complex dyes based on 5-substituted-8-hydroxyquinoline derivatives for OLED applications

We report on the photocarrier generation mechanisms in TPD and TPD-AlQ3 blend. The spontaneous as well as the field induced carrier generation efficiency is enhanced in the blend. The spontaneous carrier generation efficiency, eta0 is 0.1% in TPD and it increases to 30% in the blend. Based on our results we demonstrate a visible-blind UV detector with a response of 30 mA/W using the TPD- AIQ3 blend as the active layer.

Synthesis and characterization of spin-coatable tert-amine molecules for hole-transport in organic light-emitting diodes

Blue fluorescent 3,6-p-acetophenyl N-hexylcarbazole (ANHC) with HOMO level of -5.6 eV comparable to TPD (-5.4 eV) was synthesized. Carrier injection was found to be more efficient in OLEDs using an blend of TPD and ANHC compared to ANHC alone. The electroluminescence is red shifted in comparison to the photoluminescence of either TPD or ANHC.