Yashowanta N. Mohapatra

IIT Kanpur, Physics, Faculty Member

Physics

Professor Indian Institute of Technology KanpurInterested in Electronic Materials (Inorganic

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89 Followers 6 Following 3 Co-authorsTotal Views186 Public Mentions

Papers

Analysis of leakage current mechanism in isotype MoS2|ZnO heterostructure diodes

MoS2 is a promising layered semiconducting material, suitable for electronic and optoelectronic a... more MoS2 is a promising layered semiconducting material, suitable for electronic and optoelectronic applications due to its remarkable properties such as inherent bandgap and high mobility. However, excessive reverse bias leakage current in mechanically exfoliated MoS2 devices remains a challenge in developing electronic devices. In this work, we studied the mechanism determining reverse bias leakage current behavior in MoS2|ZnO n-n+ isotype heterostructure diodes, fabricated using multilayer MoS2 flakes obtained from two different sources, namely natural and synthetic crystals. These devices are characterized by using temperature dependent J-V characteristics in the temperature range between 145 K to 300 K as shown in Figure 1(a) and (b) for devices made on natural crystals (I-a-N), and Figure 1(c) and (d) for synthetic crystals (I-b-S), respectively. The analysis of temperature dependent J-V characteristics shows that leakage is governed by Poole- Frenkel mechanism. The linear behavio...

Analysis of leakage current mechanism in isotype MoS2|ZnO heterostructure diodes

Determination of interlayer electron mobility in multilayer MoS2 flake using impedance spectroscopy

Journal of Physics D: Applied Physics, 2021

Layered molybdenum disulfide (MoS2) is emerging as a promising candidate for novel electronic app... more Layered molybdenum disulfide (MoS2) is emerging as a promising candidate for novel electronic applications, though the focus has largely been on few-layered thin films and in-layer electrical properties. MoS2 shows various nontrivial departures in its electrical properties in comparison to isotropic crystalline materials, however the understanding of anisotropic properties, particularly of charge carrier mobility in MoS2 flakes, is meagre. We experimentally study inter-layer mobility in mechanically exfoliated MoS2 flakes. The choice of a suitable sandwich device structure enables us to study the inter-layer transport using temperature dependent current–voltage (J–V) and impedance spectroscopy. The separation of peaks in the imaginary part of impedance i.e. Im (Z) spectra due to defects and transport in the space charge limited regime allows measurement of mobility un-encumbered by other effects. We study flakes obtained from both naturally occurring and synthetic crystals. The calc...

Determination of interlayer electron mobility in multilayer MoS2 flake using impedance spectroscopy

Journal of Physics D: Applied Physics, 2021

Electrical characterization of MeV heavy-ion-induced damage in silicon: Evidence for defect migration and clustering

Journal of Applied Physics, 1998

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Luminance degradation and recovery studies in AIq3 based Organic light emitting diodes

Though organic light emitting diodes are being commercialized in many applications, issues relati... more Though organic light emitting diodes are being commercialized in many applications, issues relating to lifetime and degradation remain as fundamental concerns limiting performance. A coherent understanding of degradation mechanisms is yet to emerge. We focus on intrinsic degradation of high quality Alq3 based diodes due to electrical stressing. We monitor progressive luminance degradation and recovery by introducing well defined relaxation time windows in the current stress cycles. The method helps to clearly distinguish between recoverable and permanent degradation systematically. The voltage shift due to degradation and recovery is also monitored as a function of time. Further, we introduce a method of reconstructing the transients of the recoverable part using progressive isolated current pulses as a probe. The recovery of degradation is related to the charging and discharging of the traps in the device and our method provides a technique of measuring significant parameters of trapping through luminance transients. The origin and distinguishing features of the two types of degradation are discussed.

Disentangling degradation and auto-recovery of luminescence in Alq3 based organic light emitting diodes

Journal of Luminescence, 2014

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MoS2|ZnO isotype heterostructure diode: Carrier transport and band alignment

Journal of Applied Physics

PECVD grown hydrogenated polymorphous silicon studied using current transient spectroscopies in PIN Diodes

MRS Proceedings

Hydrogenated polymorphous silicon (pm-Si:H) has steadily emerged as a potential replacement of hy... more Hydrogenated polymorphous silicon (pm-Si:H) has steadily emerged as a potential replacement of hydrogenated amorphous silicon. Possible changes in the density of gap states due to the presence of crystallites is of central importance in understanding steady state and dynamic characteristics of devices using these materials. We have studied a-Si:H and pm-Si:H grown by PECVD at optimized conditions through the measurement of the steady state reverse current and their transients in PIN devices. The transients are analyzed using isothermal spectroscopic techniques such as Time Analyzed Transient Spectroscopy (TATS), and high resolution Laplace DLTS as a function of temperature. In case of a-Si:H, we obtain the expected signature of emission from a broad density of states in the form of stretched exponentials. In contrast the corresponding spectra for pm-Si:H are dominated by nearly exponential fast current decay processes with discrete energies between 0.20 and 0.26 eV. It is shown that...

Size Distribution Of Embedded Nano-Crystallites In Polymorphous Silicon Studied By Raman Spectroscopy And Photoluminescence

MRS Proceedings

Polymorphous Silicon (pm-Si:H) deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD) ha... more Polymorphous Silicon (pm-Si:H) deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD) has emerged as an alternative material to amorphous silicon (a-Si:H). Deposition parameters of pm-Si:H are such that small crystallites get embedded in a relaxed amorphous silicon matrix, thus improving the optical and electrical properties. We study the size of crystallites and degree of order in pm-Si:H using Raman and photoluminescence (PL) spectra of pm-Si:H and a-Si:H. Raman Spectra of a variety of hydrogenated nanostructured silicon (pmSi:H) and amorphous Silicon (a-Si:H) samples grown at different pressures were analyzed. Deconvolution of observed multiple peaks in photoluminescence spectra and fitting to Gaussian size distribution also yields particle size to be in the range of 2.3 to 3.5nm in agreement with Transmission Electron Microscopy and Raman results.

Synthesis, Photophysical, and Electroluminescent Properties of Arylenevinylenes- co -pyrrolenevinylenes Derived from Divinylaryl Bridged Bispyrroles

Macromolecules, Apr 1, 2007

Synthesis, characterization, and photophysical properties of four different π-conjugated oligomer... more

Transient based studies of organic/inorganic semiconductor hybrid structures

ABSTRACT Current developments in organic-inorganic semiconductor hybrid devices critically depend... more ABSTRACT Current developments in organic-inorganic semiconductor hybrid devices critically depend on understanding of charge carrier dynamics and properties of surfaces/interfaces between organic molecules and inorganic materials such as silicon. Zinc benzathiozole, (Zn (BZT) _2) is a nearly white photoluminescent material and has promise for white LED applications. However, much of the charge process mechanisms for the material is not known. We study charge processes in such a hybrid structure by monitoring changes in space charge layer formed at junction of O/I hybrid structure. We study Al/ Zn (BZT)2 / n-Si hybrid device structure using a variety of techniques such as C-V characteristics, DLTS and Time analysed transient spectroscopy (TATS). Charge trapping centers ranging from 1.2eV to 0.25eV are observed alongwith unusual lineshape for some including processes faster than exponential. We demonstrate usefulness of these studies in distinguishing between origin of charge emission processes in such hybrid systems.

Mobility with negative coefficient in Poole–Frenkel field dependence in conjugated polymers: Role of injected hot electrons

Organic Electronics, 2010

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Time Analyzed Transient Spectroscopy to Monitor Carrier Dynamics at Deep Level Defects in Polymeric Semiconductors

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Technical Education and Indian Society: The Role of Values

Nanotechnology and the Challenges of Equity, Equality and Development, 2010

While much of this volume focuses on the role of equity in technologies, political structures, th... more

Compound formation under local thermal spikes during ion-beam mixing: Model and its experimental verification

Physical review. B, Condensed matter, Jan 15, 1996

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The Kinetics of Capture and Emission of Discrete DX Related Centers in Silicon Doped AlGaAs Using Time Analyzed Transient Spectroscopy

MRS Proceedings, 1995

The kinetics of multiple DX related emission centers are studied using the isothermal Time Analyz... more The kinetics of multiple DX related emission centers are studied using the isothermal Time Analyzed Transient Spectroscopy (TATS) of constant capacitance voltage transients. Four distinct emitting centers have been obtained using higher order TATS in the same silicon doped Al0.33As0.67As sample without use of hydrostatic pressure. Accurate identification of the multiple DX states has allowed a better understanding of the charge redistribution process during capture. Improved resolution due to increase in order of spectroscopy has enabled quantitative fitting of spectral lineshape and thus accounting for degree of nonexponentiality associated with each of the four discrete centers. The capture kinetics of these centers are studied over six orders in magnitude of filling time. The resulting quality of kinetic data makes possible detailed quantitative comparison with kinetics predicted by positive U and negative U models of DX centers. We show that our data is in agreement with positiv...

Field and Thickness Dependence of Mobility of Organic Semiconductors determined using Photocurrent Transients

ABSTRACT We investigate the suitability of the photocurrent transient method, similar to the time... more ABSTRACT We investigate the suitability of the photocurrent transient method, similar to the time-of-flight technique, in determining the carrier mobility of practical devices having active layer thicknesses in the nanometer range. The designed samples are in the form of homojunction and heterojunction device structures consisiting of p-doped and undoped layers which resembles the present day commercial organic light emitting diodes. The materials under consideration are m-MTDATA and Alq3. Distinct photocurrent transient signals were obtained under forward and reverse biased conditions corresponding to the mobility of the two different charge carriers. The mobility values obtained showed field and thickness dependence with an unusual negative field activation coefficient ‘β’.

Correlation of I-V and C-V characteristics of single layer diodes for popular active organic materials

ABSTRACT Even though display based products of organic semiconductors have started getting commer... more ABSTRACT Even though display based products of organic semiconductors have started getting commercialized, the charge processes and trap effects on the devices are not well understood. Though voltage (V) dependence of current (I) and capacitance (C) have been extensively studied in the literature, there are several features which are yet to be coherently explained. There have been several reports on the origin of C-V peaks attributing them to various mechanisms such as competition between diffusion and drift, traps, and carrier recombination etc. However, there is lack of knowledge on the origin of the nature of the C-V peak. In this paper we carry out a correlated study of I-V and C-V characteristics as a function of temperature for four different popular active materials to obtain a better understanding of underlying mechanisms. High quality diodes are fabricated with low leakage current so as to obtain large rectification. In the case of MEH-PPV and NPB, I-V characteristics show temperature independent hysteresis and signature of charge storage at interfaces. This is absent in P3HT:PCBM and pentacene:C60 based devices. In the case of MEH-PPV, pentacene:C60 and NPB, the shape of the C-V are similar (rises sharply but falls slowly) but the amplitude of the peaks varies with temperature. We correlate this to competition between drift diffusion giving rise to the peak. In the case of the P3HT:PCBM the shape is almost symmetrical on both sides of the peak, which seems to arise from the recombination losses. The peak positions are independent of temperature (in the range studied) in all these cases. In the case of pentacene:C60, as the temperature is increased, a second peak in C-V starts to appear. From the I-V, it is very clear that it is related to trapping phenomena. A thorough analysis of data is shown in Figure 1 and generalized view of correlation between I-V and C-V will be presented.