E S Kannan

Non-degenerate n-type doping by hydrazine treatment in metal work function engineered WSe₂ field-effect transistor.

We report a facile and highly effective n-doping method using hydrazine solution to realize enhanced electron conduction in a WSe2 field-effect transistor (FET) with three different metal contacts of varying work functions-namely, Ti, Co, and Pt. Before hydrazine treatment, the Ti- and Co-contacted WSe2 FETs show weak ambipolar behaviour with electron dominant transport, whereas in the Pt-contacted WSe2 FETs, the p-type unipolar behaviour was observed with the transport dominated by holes. In the hydrazine treatment, a p-type WSe2 FET (Pt contacted) was converted to n-type with enhanced electron conduction, whereas highly n-doped properties were achieved for both Ti- and Co-contacted WSe2 FETs with on-current increasing by three orders of magnitude for Ti. All n-doped WSe2 FETs exhibited enhanced hysteresis in their transfer characteristics, which opens up the possibility of developing memories using transition metal dichalcogenides.

Capacitance-voltage and current-voltage characteristics of graphite oxide thin films patterned by ultraviolet photolithography

Electrical characteristics of graphite oxide (GO) thin films deposited on a p-type silicon substrate were investigated to explore its potential application as a dielectric material in organic field effect transistors. Channel current in the GO films exhibited linear response with the applied bias in the positive voltage regime and increased exponentially for negative source-drain bias. This rectifying behavior arises due to the Coulombic interaction between the electrons emitted from the metal contact and the space charge region in the GO film. A clockwise hysteresis loop was observed in the capacitance-voltage characteristics due to the presence of traps at the interface.

Memory characteristics of InAs quantum dots embedded in GaAs quantum well

The memory characteristics of InAs based quantum dot (QD) memory devices has been investigated by carrying out capacitance-voltage and current-voltage measurements. The dots which were embedded in the GaAs quantum well were charged by the electrons from the two dimensional electron gas and a clockwise hysteresis loop is observed on cyclically sweeping the gate bias. The number of trapped electrons is found to be two orders of magnitude lesser than the QD density. Interdot Coulombic interactions and phonon assisted electron tunneling was found to significantly affect the charge trapping ability of the QDs.

Energy free microwave based signal communication using ratchet effect

The ratchet based microwave detectors are implemented as receivers of amplitude, frequency, and pulse width modulated signals. The detector has a peak responsivity of 994 V/W and has excellent signal to noise ratio in the measurement bandwidth with its noise equivalent power of about 0.01 pico W/√Hz and 6.3 × 107 cm√Hz/W detectivity. The frequency limit of detection can be tuned by a suitable choice of the antidot parameters. The advantages of the utilizing ratchet based active antennas are simple circuitry, controllable spectral range, no power consumption, and natural rejection of stray electromagnetic radiations.

Charge trapping in quantum dot memory devices with different dot densities

The memory characteristics of electrically driven quantum dot (QD) memory devices with different dot densities were investigated by capacitance–voltage (C–V) and current–voltage (I–V) measurements at 100 K. The dots which were embedded in the GaAs quantum well were charged by the electrons from the two-dimensional electron gas at positive gate bias. On cyclically sweeping the gate bias, a clockwise hysteresis loop is observed in the capacitance and conductance trace. The number of trapped electrons was found to decrease slightly as the density of the dots increases from 1.2 to 3 × 109 dots cm−2. Our study reveals that inter-dot tunnelling coupled with Coulombic interaction between the dots and the charged traps in the plane containing the QDs was found to significantly affect the charge trapping ability of the QDs.

Short range scattering effect of InAs quantum dots in the transport properties of two dimensional electron gas

Short range interaction between two dimensional electron gas (2DEG) and InAs quantum dots embedded in the GaAs∕AlGaAs quantum well is investigated as a function of carrier density. At low carrier density the interaction is significantly characterized by a transport to quantum lifetime ratio of less than 5. However, with an increase in carrier density, quantum lifetime is observed to undergo a sharp transition from 0.17to0.25ps. This is attributed to the screening of short range repulsive scattering due to InAs quantum dots by the 2DEG.

Molybdenum disulfide nanoparticles decorated reduced graphene oxide: highly sensitive and selective hydrogen sensor

In this work, we report on the hydrogen (H2) sensing behavior of reduced graphene oxide (RGO)/molybdenum disulfide (MoS2) nano particles (NPs) based composite film. The RGO/MoS2 composite exhibited a highly enhanced H2 response (∼15.6%) for 200 ppm at an operating temperature of 60 °C. Furthermore, the RGO/MoS2 composite showed excellent selectivity to H2 with respect to ammonia (NH3) and nitric oxide (NO) which are highly reactive gas species. The composites response to H2 is 2.9 times higher than that of NH3 whereas for NO it is 3.5. This highly improved H2 sensing response and selectivity of RGO/MoS2 at low operating temperatures were attributed to the structural integration of MoS2 nanoparticles in the nanochannels and pores in the RGO layer.

High performance MoS2-based field-effect transistor enabled by hydrazine doping.

We investigated the n-type doping effect of hydrazine on the electrical characteristics of a molybdenum disulphide (MoS2)-based field-effect transistor (FET). The threshold voltage of the MoS2 FET shifted towards more negative values (from -20 to -70 V) on treating with 100% hydrazine solution with the channel current increasing from 0.5 to 25 μA at zero gate bias. The inverse subthreshold slope decreased sharply on doping, while the ON/OFF ratio increased by a factor of 100. Gate-channel coupling improved with doping, which facilitates the reduction of channel length between the source and drain electrodes without compromising on the transistor performance, making the MoS2-based FET easily scalable.

Reduced graphene oxide produced by rapid-heating reduction and its use in carbon-based field-effect transistors

Highly conductive and water-dispersible sheets of reduced graphene oxide (RGO) were produced by rapidly heating graphene oxide (GO) paper at a low temperature (300 °C) for a short processing time of 3 s. The GO paper was thermally treated during the rapid-heating reduction process and, consequently, the oxygen functional groups in the obtained RGO were highly reduced. The RGO film displays good thermal stability, crystallinity, low sheet resistance, and good dispersibility in water, which makes it an ideal candidate to be used in various carbon-based electronic devices. We finally demonstrate the suitability of RGO as an active channel material and as a source-drain electrode for graphene field-effect transistors, which bring the possibility of realizing all-carbon devices a step closer to reality.

In situ reduced graphene oxide interlayer for improving electrode performance in ZnO nanorods

The effect of reduced graphene oxide (RGO) thin film on the transport characteristics of vertically aligned zinc oxide nanorods (ZnO NRs) grown on ITO substrate was studied. GO was uniformly drop casted on ZnO NRs as a passivation layer and then converted into RGO by heating it at 60 °C prior to metal electrode deposition. This low temperature reduction is facilitated by the thermally excited electrons from ZnI interstitial sites (~30 meV). Successful reduction of GO was ascertained from the increased disorder band (D) intensity in the Raman spectra. Temperature (298 K–10 K) dependent transport measurements of RGO–ZnO NRs indicate that the RGO layer not only acts as a short circuiting inhibitor but also reduces the height of the potential barrier for electron tunneling. This is confirmed from the temperature dependent electrical characteristics which revealed a transition of carrier transport from thermionic emission at high temperature (T > 100 K) to tunneling at low temperature (T < 100 K) across the interface. Our technique is the most promising approach for making reliable electrical contacts on vertically aligned ZnO NRs and improving the reproducibility of device characteristics.