N-type Indium Tin Oxide Research Articles

Effect of Annealing Temperature on Radio Frequency Sputtered p-Type Delafossite Copper Chromium Oxide (CuCrO2) Thin Films and Investigation of Diode Characteristics Forming Transparent pn-Heterojunction

For the first time, the deposition of CuCrO2 thin films was carried out using a dual-target RF magnetron sputtering technique using Cu2O and Cr2O3 targets. The deposited films were subsequently annealed in N2 ambiance from 600–900 °C. This work reports that the electrical, optical, structural, and morphological properties of CuCrO2 thin films are significantly affected due to the variation in the annealing temperature. XRD analysis confirms the presence of single-phase CuCrO2 in the films annealed at 650 °C. The presence of Cu in the 1+ oxidation state in the phase pure CuCrO2 thin films was confirmed through XPS analysis. Further, through XPS analysis, the oxidation states of Cu and Cr, the full-width half maximum (FWHM), the peak positions, and their respective binding energies have been elucidated. SEM analysis confirms the promotion of nanocrystalline growth in the thin films as the annealing temperature was increased from 600 °C. The average grain size increased from 40.22 nm to 105.31 nm as the annealing temperature was increased from 600 to 900 °C. Optical studies conducted in the wavelength range of 200 nm to 800 nm revealed a decrease in the optical transmission and optical bandgap with an increase in the annealing temperature. The highest optical transmission of ~81% and an optical bandgap of 3.21 eV were obtained for the films depicting the delafossite nature of CuCrO2. The optical bandgap was found to vary between 3.16 eV and 3.74 eV for the films studied in this research. The lowest resistivity of 0.652 Ω cm was obtained for the films annealed at 650 °C. Transparent heterojunction diodes involving p-type delafossite copper chromium oxide (CuCrO2) and n-type indium tin oxide (ITO) were fabricated. The best diode depicted a cut-in voltage of 0.85 V, a very low leakage current of 1.24 x 10-8, an ideality factor of 4.13, and a rectification ratio of 2375.

Optical Modulation via Coupling of Distributed Semiconductor Heterojunctions in a Si -ITO-Based Subwavelength Grating

A mechanism of optical intensity modulation is proposed by utilizing the electro-optic coupling in distributed semiconductor heterojunctions of p-type silicon ($\mathrm{Si}$) and n-type indium tin oxide (ITO) in the form of the subwavelength grating in a rib waveguide. The coupled multiple semiconductor heterojunctions of $\mathrm{Si}$-ITO are made to exhibit efficient optical intensity modulation via electrically tunable permittivity of ITO. The subwavelength grating is a nanophotonic element that not only provides a way to couple multiple heterojunctions, but it also gives rise to efficient optical (fiber to chip) coupling at a wavelength of 1550 nm. Lateral coupling of distributed heterojunctions via depleted charge density distributed along vertical and horizontal directions enable the device to show a high extinction ratio of 24 dB. Also, electrical tuning of the coupling efficiency for an 80-\textmu{}m long device is reported, which exhibits the multifunctional nature of the proposed nanophotonic device. The proposed modulation scheme, with a modulation efficiency of 0.34 V/mm and energy consumption of 36 pJ, may open pathways for energy-efficient compact devices and circuits for large-scale optoelectronic integration. The proposed mechanism of optical modulation takes advantage of distributed semiconductor heterojunctions and enables electrically tunable inherent optical coupling with a nanophotonic element called a subwavelength grating, which further improves the modulation performance compared with a conventional $\mathrm{Si}$-ITO heterojunction.

I-V Characteristics of Cadmium Telluride Quantum Dots Diode Fabricated by Drop Casting Method

Current (I)-Voltage (V) characterizations of a CdTe quantum dot diode is discussed in this article. The quantum dot diode is fabricated by a simple drop casting method on an n-type Indium Tin Oxide glass substrate. The linear variation of current with respect to applied voltage can be attributed to reduced grain boundary defects and enriched crystallinity. It is also observed that quantum dots can show good current conduction than CdTe nano-rods.

I-V Characteristics of Cadmium Telluride Quantum Dots Diode Fabricated by Drop Casting Method

Current (I)-Voltage (V) characterizations of a CdTe quantum dot diode is discussed in this article. The quantum dot diode is fabricated by a simple drop casting method on an n-type Indium Tin Oxide glass substrate. The linear variation of current with respect to applied voltage can be attributed to reduced grain boundary defects and enriched crystallinity. It is also observed that quantum dots can show good current conduction than CdTe nano-rods.

A High Gain Low-Noise Amplifier Based on ITO-Stabilized ZnO Thin-Film Transistors

A novel high gain low-noise analog amplifier based on n-type indium tin oxide (ITO)-stabilized ZnO thin-film transistors (TFTs) was studied in this work. Amplifiers with capacitor bootstrap structure are proposed. The effect of unequal numbers of bootstrap structure, various capacitance, and different circuit topology on the gain and noise of circuits were investigated. The input referred noise of five kinds of amplifier circuits, Amp1, Amp2 (C444, C333, C422), and Amp3 were measured to be 101.1, 44, 47.3, 43.5, and $38.3~\mu \text{V}_{rms}$ , respectively, and the gains are 19.5, 28.8, 26.8, 25.7, and 32 dB, respectively. It is found that as the numbers of bootstrap structure increase in a small range, the input referred noise decreases, and the circuit gain increases. The effects of the capacitance on the gain or noise can be negligible. And also, the gain of the circuit with cascode structure is higher than that with common source. Results show that the noise is much lower than that of a-InGaZnO (IGZO) TFTs technology, which is widely used in TFT circuits design. The proposed high gain and low-noise analog amplifier with the ITO-stabilized ZnO TFTs technology has great potential in the biomedical fields like electro cardiogram (ECG) and pulse detection, as well as wearable electronic applications.

Transparent flexible thin-film p\u2013n junction thermoelectric module

Transparent and flexible thermoelectrics has been highly sought after for future wearable devices. However, the main stumbling block to prevent its widespread adoption is the lack of p-type transparent thermoelectrics and the stringent criteria of electrical and thermal properties matching appropriately between p-legs and n-legs. This work demonstrates the fabrication of p-type PEDOT:PSS films whose optical properties, electrical conductivity, thermal conductivity, and Seebeck coefficient were engineered to perfectly match the n-type indium tin oxide (ITO) counterparts. The dense p-type PEDOT:PSS and n-type ITO thin films show a thermoelectric figure of merit of zT = 0.30 and 0.29 at 450 K, and a thermal conductivity of 0.22 and 0.32 W m−1 K−1, respectively. A flexible thermoelectric generator (TEG) module with a high transmittance of >81% in the visible wavelength range of 400–800 nm is fabricated using 10 pairs of p-type PEDOT:PSS and n-type ITO thin film legs. An ultra-high power density of 22.2 W m−2 at a temperature gradient of 80 K was observed, which is the highest power density reported for organic/hybrid-based flexible TEGs so far. Our transparent flexible thin-film p–n junction thermoelectric module with exceptionally high power generation may take a tremendous step forward towards multi-functional wearable devices.

Understanding Transport in Hole Contacts of Silicon Heterojunction Solar Cells by Simulating TLM Structures

Silicon heterojunction (SHJ) solar cell device structures use carrier-selective contacts that enable efficient collection of majority carriers while impeding the collection of minority carriers. However, these contacts can also be a source of resistive losses that degrade the performance of the solar cell. In this article, we evaluate the performance of the carrier-selective hole contact- hydrogenated amorphous silicon (a-Si:H)(i)/a-Si:H(p)/indium tin oxide (ITO)/Ag-by simulating transport in SHJ solar cell transfer length method structures. We study contact resistivity behavior by varying the a-Si:H(i) layer thickness, ITO(n±) and a-Si:H(p) layer doping, temperature, and interface defect density at the a-Si:H(i)/ crystalline silicon (c-Si) interface. In particular, we consider the effect of ITO/a-Si:H(p) and the a-Si:H(i)/c-Si heterointerfaces on contact resistivity as they play a crucial role in modulating transport through the hole contact structure. Transport models such as band-to-band tunneling, and thermionic emission models were added to describe transport across the heterointerfaces. Until now, most simulation studies have treated the ITO as a Schottky contact; in this article, we treat the ITO as an n-type semiconductor. Our simulations match well with corresponding experiments conducted to determine contact resistivity. As the a-Si:H(i) layer thickness is increased from 4 to 16 nm, the simulated contact resistivity increases from 0.50 to 2.1 Ωcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which deviates a maximum of 8% from the experimental measurements. It should be noted that we calculate the contact resistivity for the entire hole contact stack, which takes into account transport across the a-Si:H(p)/c-Si and ITO/a-Si:H(p) heterointerface. Corresponding experiments on cell structures showed a fill factor degradation from 77% to 70%. Our simulations indicate that a highly doped n-type ITO layer facilitates tunneling at the ITO/a-Si:H(p) heterointerface, which leads to low contact resistivities.

Optical Modulation in Hybrid Waveguide Based on Si-ITO Heterojunction

An Optical modulator based on a hybrid optical waveguide made up of Silicon and Indium Tin Oxide (ITO) is proposed. The hybrid waveguide is created by the coupling of a leaky optical mode guided in silicon with ITO. The optical modulation is realized with the heterojunction between p-type silicon and n-type ITO. The presence of ITO causes electrical tuning in permittivity and in imaginary-part of the refractive index which provide a way to modulate the intensity of the guide optical mode. The device with Si-ITO heterojunction is fabricated to show intensity modulation at 1.55 μm wavelength. To achieve an efficient optical modulation the carrier concentration of ITO is optimized by depositing ITO on p-type Si wafer at different oxygen partial pressures using Ion assisted electro-beam deposition. The fabricated device exhibiting an extinction ratio of 7 dB for 1.7 mm long device at low voltage of −5 volts.

MoOx modified ITO/a-Si:H(p) contact for silicon heterojunction solar cell application

Schottky barrier is a fundamental problem when contacting n-type indium tin oxide with p-type hydrogenated amorphous silicon due to their mismatched work functions in silicon heterojunction solar cell. Here, we developed a facile and effective method to modify the electrical properties of ITO/a-Si:H(p) contact by thermal evaporation an ultrathin MoOx buffer layer. The transient photo-conductance decay measurements showed that both effective carrier lifetime and implied open-circuit voltage increased abruptly after inserting an ultrathin MoOx buffer layer, from 1.43ms to 2.28ms and 735mV to 744mV, respectively, which is mainly attributed to modification of MoOx buffer layer on the Schottky barrier at the interface of ITO/a-Si:H(p) contact. By modulating the thickness of MoOx buffer layer, the MoOx based SHJ solar cell illustrated a champion efficiency up to 21.8%, companying with an absolute Voc gain over 8mV, and fill factor gain over 1.5%, respectively.

Fabrication of p-type ZnO nanofibers by electrospinning for field-effect and rectifying devices

Ce-doped p-type ZnO nanofibers were synthesized by electrospinning and followed calcinations. The surface morphology, elementary composition, and crystal structure of the nanofibers were investigated. The field effect curve confirms that the resultant Ce-doped ZnO nanofibers are p-type semiconductor. A p-n heterojunction device consisting of Ce-doped p-type ZnO nanofibers and n-type indium tin oxide (ITO) thin film was fabricated on a piece of quartz substrate. The current-voltage (I-V) characteristic of the p-n heterojunction device shows typical rectifying diode behavior. The turn-on voltage appears at about 7 V under the forward bias and the reverse current is impassable.

Fabricate Heterojunction Diode by Using the Modified Spray Pyrolysis Method to Deposit Nickel–Lithium Oxide on Indium Tin Oxide Substrate

P-type lithium-doped nickel oxide (p-LNiO) thin films were deposited on an n-type indium tin oxide (ITO) glass substrate using the modified spray pyrolysis method (SPM), to fabricate a transparent p-n heterojunction diode. The structural, optical, and electrical properties of the p-LNiO and ITO thin films and the p-LNiO/n-ITO heterojunction diode were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), UV-visible spectroscopy, Hall effect measurement, and current-voltage (I-V) measurements. The nonlinear and rectifying I-V properties confirmed that a heterojunction diode characteristic was successfully formed in the p-LNiO/n-ITO (p-n) structure. The I-V characteristic was dominated by space-charge-limited current (SCLC), and the Anderson model demonstrated that band alignment existed in the p-LNiO/n-ITO heterojunction diode.

Preparation and Characterization of p-Ag2O/n-Si Heterojunction Devices Produced by Rapid Thermal Oxidation

The thermal evaporation system type (Edwards) has been used to evaporate high purity (99.9%) silver on quartz and (n-type) silicon substrates at room temperature under low pressure (about10-6torr) for different thickness (50, 100, and 150) nm. Using a rapid thermal oxidation (RTO) of Ag film at oxidation temperature 250 oC and oxidation times 60sec, Ag2O thin film was prepared. The structural, optical and electrical properties of Ag2O film were investigated and compared with other published results. The structural investigation showed that the films formed at thickness 150nm showed (111) strong reflection along with weak reflections of (200) and (103) correspond to the growth of single phase Ag2O with cubic structure. Optical properties revealed that these films having direct optical band gap of (2.4, 2.3, 2.1) eV at different film thickness with high transparency in visible and NIR regions. Dark and illuminated I-V, CV, and spectral responsivity of p-Ag2O/n-Si heterojunction were investigated and discussed. Ohmic contacts were fabricated by evaporating 99.999 purity aluminum and gold wires for back contact and front contact respectively. Ag2O thin film was also prepared on n-type indium tin oxide (ITO) thin films to investigate the I-V characteristic of p-Ag2O/n-ITO junction.

Fabrication of highly transparent self-switching diodes using single layer indium tin oxide

The fabrication of a self-switching diode (SSD) from a single layer of n-type indium tin oxide [In2O3:Sn (ITO)] is reported. The material was grown using reactive thermal evaporation and nanostructured using a focused ion beam. The resultant device demonstrates strong current rectification, as well as a high threshold and breakdown voltage, owing to the higher density of states associated with the material, when compared to other reported SSD-device material. It is shown that this work could potentially lead to a range of new transparent devices based on ITO, without the need to develop high quality p-type material.

Carrier concentration dependence of optical Kerr nonlinearity in indium tin oxide films

Optical Kerr nonlinearity (n2) in n-type indium tin oxide (ITO) films coated on glass substrates has been measured using Z-scans with 200-fs laser pulses at wavelengths ranging from 720 to 780 nm. The magnitudes of the measured nonlinearity in the ITO films were found to be dependent on the carrier concentration with a maximum n2-value of 4.1 x 10-5 cm2/GW at 720-nm wavelength and an electron density of Nd = 5.8 x 1020 cm-3. The Kerr nonlinearity was also observed to be varied with the laser wavelength. By employing a femtosecond time-resolved optical Kerr effect (OKE) technique, the relaxation time of OKE in the ITO films is determined to be ~1 ps. These findings suggest that the Kerr nonlinearity in ITO can be tailored by controlling the carrier concentration, which should be highly desirable in optoelectronic devices for ultrafast all-optical switching.

Characteristics of Thin-Film p-ZnMgO/n-ITO Heterojunctions on Glass Substrates

Thin films of oriented, polycrystalline p-type Zn 0 . 9 Mg 0 . 1 O were deposited on n-type indium-tin oxide (ITO)-coated glass substrates by pulsed laser deposition at 400°C to form transparent wide bandgap heterojunctions. The characteristics of Au, Ni, or Pt contacts subsequently deposited on these heterojunction layers were examined. In each case, rectifying behavior of the p-n junction was obtained. The junctions display a negative temperature coefficient for reverse breakdown voltage. This approach looks promising as a means of realizing low-cost-substrate transparent electronics.

Electrical characterization of transparent p–i–n heterojunction diodes

Transparent p–i–n heterojunction diodes are fabricated using heavily doped, p-type CuYO2 and semi-insulating i-ZnO thin films deposited onto a glass substrate coated with n-type indium tin oxide. Rectification is observed, with a ratio of forward-to-reverse current as high as 60 in the range −4–4 V. The forward-bias current–voltage characteristics are dominated by the flow of space-charge-limited current, which is ascribed to single-carrier injection into the i-ZnO layer. Capacitance measurements show strong frequency dispersion, which is attributed to i-ZnO traps. The diode structure has a total thickness of 0.75 μm and an optical transmission of ∼35%–65% in the visible region.

Visible electroluminescence from porous silicon np heterojunction diodes

We report the preparation of silicon-based visible light-emitting diodes, configured as heterojunctions between porous silicon (formed by electrochemical etching of p-type silicon wafers), and n-type indium tin oxide (ITO). The transparent ITO film allows light emission through the top surface of the device, under a forward electrical bias of several volts across the junction. Photogenerated currents are observed under reverse biases. A tentative model for this electroluminescence is presented, based on injection of minority carriers through a narrow interphase region into the porous silicon structure, where radiative recombination occurs.