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To develop suitable ferromagnetic oxides with Curie temperature (TC) at or above room temperature for spintronic applications, a great deal of research in doping ZnO with magnetic ions is being carried out over last decade. As the experimental results on magnetic ions doped ZnO are highly confused and controversial, we have investigated ferromagnetism in non-magnetic ion, Ag, doped ZnO. When Ag replaces Zn in ZnO, it adopts 4d9 configuration for Ag2+ which has single unpaired spin and suitable exchange interaction among these spins gives rise to ferromagnetism in ZnO with above room temperature TC. Experimentally, we have observed room temperature ferromagnetism (RTFM) in Ag-doped ZnO with Ag concentration varied from 0.03% to 10.0%. It is shown that zinc vacancy (VZn) enhances the ferromagnetic ordering (FMO) while oxygen vacancy (VO) retards the ferromagnetism in Ag-doped ZnO. Furthermore, the theoretical investigation revealed that VZn along with Ag2+ ions play a pivotal role for RTFM in Ag-doped ZnO. The Ag2+-Ag2+ interaction is ferromagnetic in the same Zn plane whereas anti-ferromagnetic in different Zn planes. The presence of VZn changes the anti-ferromagnetic to ferromagnetic state with a magnetic coupling energy of 37 meV. Finally, it has been established that the overlapping of bound magnetic polarons is responsible for RTFM in low doping concentration. However, anti-ferromagnetic coupling sets in at higher doping concentrations and hence weakens the FMO to a large extent. [ABSTRACT FROM AUTHOR]

Charge transport in organic thin films which are generally polycrystalline is typically limited by the localization of the carriers at lattice defects resulting in low carrier mobilities and carriers move from one state to another state by hopping. However, charge transport in organic semiconductors in their single crystalline phase is coherent due to band conduction and mobilities are not limited by disorder resulting in higher carrier mobility. So it is a challenge to enhance the carrier mobility in a thin film which is the preferred choice for all organic devices. Here, we show that it is possible to increase the carrier mobility in polycrystalline thin films by injecting sufficient carriers such that Fermi level can be moved into the region of high density in Gaussian density of states of molecular solids. When the hopping transport happens through the molecular energy levels whose density is low, mobility is decided by incoherent transport however, when the the hopping transport happens through the energy levels with high density, mobility is decided by coherent transport, as in band conduction. We present results highlighting the observation of both band-like and hopping conduction in polycrystalline organic thin films by varying the concentration of injected charge. More importantly the transition from hopping to band transport is reversible. The observed carrier mobilities in both the regimes match well with theoretical estimates of hopping mobility and band mobility determined from first principles density functional theory. [ABSTRACT FROM AUTHOR]

Here we report an investigation on ZnO and metal phthalocyanine (MePc) based heterostructures for inorganic/organic hybrid p-n junction diodes using temperature dependent current-voltage (J-V) and capacitance-voltage (C-V) characteristics. The J-V characteristics of the ZnO/MePc’s based hybrid p-n junction diode are asymmetrical with a rectification ratio of 104 indicating the formation of a depletion layer, which has also been corroborated by C-V characteristics. The mechanism of device operation has been revealed by the temperature dependence of the ideality factor and saturation current-density. These results indicate that operation of a hybrid p-n junction diode can be described by tunneling enhanced bulk recombination. [ABSTRACT FROM AUTHOR]

Highly conducting and transparent Ga-doped ZnO (GZO) thin films have been grown on transparent substrates at different growth temperatures with Ga content varying from 0.01% to 10%. All films showed pronounced c-axis orientation corresponding to hexagonal wurtzite structure. The minimum resistivity of 4.3 × 10 Ω cm was reproducibly obtained in GZO thin film doped with 2% Ga and grown at 600°C. We have further shown that highly conducting transparent GZO thin film can be used as a Schottky contact in copper phthalocyanine (CuPc)-based Schottky diodes. The capacitance-voltage characteristics of the Al/CuPc/Au and GZO/CuPc/Au Schottky diodes show similar built-in potential ( V) of 0.98 V, which is close to the difference in work function between Au (5.2 eV) and Al or GZO (4.2 eV), establishing that GZO behaves as a metal electrode with work function similar to Al. Similar values of acceptor concentration (∼10 cm) in CuPc were obtained from the capacitance-voltage characteristics of the Al/CuPc/Au and GZO/CuPc/Au Schottky diodes. These observations indicate the absence of interface states at the metal/organic interface in CuPc-based Schottky diodes. [ABSTRACT FROM AUTHOR]

Highly conducting transparent indium-doped zinc oxide (IZO) thin films have been achieved by controlling different growth parameters using radio frequency magnetron sputtering. The structural, electrical, and optical properties of the IZO thin films have been investigated for varied indium content and growth temperature ( T) in order to find out the optimum level of doping to achieve the highest conducting transparent IZO thin films. The highest mobility and carrier concentration of 11.5 cm/V-s and 3.26 × 10 cm, respectively, have been achieved in IZO doped with 2% indium. It has been shown that as T of the 2% IZO thin films increase, more and more indium atoms are substituted into Zn sites leading to shift in (002) peaks towards higher angles which correspond to releasing the stress within the IZO thin film. The minimum resistivity of 5.3 × 10 Ω-cm has been achieved in 2% indium-doped IZO grown at 700°C. [ABSTRACT FROM AUTHOR]

It is widely reported during last decade on the observation of room temperature ferromagnetism (RTFM) in doped ZnO and other transition metal oxides. However, the origin of RTFM is not understood and highly debated. While investigating the origin of RTFM, magnetic ion doped oxides should be excluded because it is not yet settled whether RTFM is intrinsic or due to the magnetic ion cluster in ZnO. Hence, it is desirable to investigate the origin of RTFM in non-magnetic ion doped ZnO and Cu-doped ZnO will be most suitable for this purpose. The important features of ferromagnetism observed in doped ZnO are (i) observation of RTFM at a doping concentration much below than the percolation threshold of wurtzite ZnO, (ii) temperature independence of magnetization and (iii) almost anhysteretic magnetization curve. We show that all these features of ferromagnetism in ZnO are due to overlapping of bound magnetic polarons (BMPs) which are created by exchange interaction between the spin of Cu2+ ion and spin of the localized hole due to zinc vacancy (VZn). Both the experimental and theoretical investigation show that the exchange interaction between Cu2+-Cu2+ ions mediated by VZn is responsible for RTFM in Cu-doped ZnO. [ABSTRACT FROM AUTHOR]