High Quality P-type Research Articles

Nanohybrids that consisit of p-type, nitrogen-doped ZnO and graphene nanostructures: synthesis, photophysical properties, and biosensing application

ZnO, a promising material for optoelectronic applications, has attracted considerable attention due to its wide and direct band gap and large exciton binding energy. To understand the applications of this material, fabrication of high quality p-type ZnO is a key step. However, a reliable p-type doping of this material remains a major challenge. In this study, we report p-type nitrogen-doped ZnO nanoparticle, grown in a nitrogen doped graphene layer matrix by a plasma heating process using a natural protein and zinc nitrate as the precursors. The structural characterizations are developed by several microscopic techniques including the field emission electron microscopy, high resolution transmission electron microscopy, x-ray photoelectron spectroscopy, and micro-Raman analysis. In addition, the ultraviolet (UV)–visible absorption characteristics and photoluminescence properties of the samples are studied. Its p-type conduction behaviour is confirmed by the Hall effect measurement, which was ascribed to the high nitrogen dopant concentration in the Zn-poor ZnO, and the related mechanism for the p-type behaviour is also discussed. Moreover, the results of the glucose detection based on the strong green luminescence of glucose indicate that the nitrogen-doped ZnO nanodots/nitrogen-doped graphene layer nanohybrid is also a competitive candidate in the biosensing field.

Structural and thermoelectric properties of nanostructured p-SnO thin films grown by e-beam evaporation method

Today, the earnest need for earth-abundant and environmentally friendly thermoelectric materials has revealed the importance of semiconductor metal oxides in order to eliminate the barrier towards their wide-ranging use in industrial applications. In the present work, we demonstrate the synthesis of p-type tin oxide thin films on quartz glass and Si substrates by using electron beam evaporation technique followed by rapid thermal annealing process at 200 °C for 20 min in Ar-atmosphere. Annealing-induced structural, electrical, optical and thermoelectric properties of pristine and annealed SnO thin films are primarily studied. The compositional and structural analysis of SnO films are performed by using X-Ray Diffraction, Scanning Electron Microscope as well as Atomic Force Microscope. Moreover, the mechanism of thermoelectric transportation at different measurement temperatures is deeply inspected via thermoelectric measurements. The Seebeck coefficient, carrier concentration and hole mobility in conjunction with the development of thin film nanostructures are discussed, predominantly. The optimal annealing may tune structural, electro-optic and thermoelectric properties of SnO films for the commercial-level maturity of thermoelectric devices for energy applications. • Synthesis of high quality p-type SnO thin films by e-beam evaporation method. • Phase stability can be achieved by optimal annealing of tin oxide thin films. • Electrical resistivity and mobility affects the thermoelectric properties. • Optimal annealing reduces the crystal imperfections and band-tail states in SnO films. • The air-annealing induces the phase transition in SnO x thin films.

Two-valence band electron and heat transport in monocrystalline PbTe-CdTe solid solutions with Cd content up to 10 atomic percent

High quality p-type PbTe-CdTe monocrystalline alloys containing up to 10 at.$\%$ of Cd are obtained by self-selecting vapor transport method. Mid infrared photoluminescence experiments are performed to follow the variation of the fundamental energy gap as a function of Cd content. The Hall mobility, thermoelectric power, thermal conductivity and thermoelectric figure of merit parameter $ZT$ are investigated experimentally and theoretically paying particular attention to the two-valence band structure of the material. It is shown that the heavy-hole band near the $\Sigma$ point of the Brillouin zone plays an important role and is responsible for the Pb$_{1-x}$Cd$_x$Te hole transport at higher Cd-content. Our data and their description can serve as the standard for Pb$_{1-x}$Cd$_x$Te single crystals with $x$ up to 0.1. It is shown, that monocrystalline Pb$_{1-x}$Cd$_x$Te samples with relatively low Cd content of about 1 at.\% and hole concentration of the order of 10$^{20}$ cm$^{-3}$ may exhibit $ZT \approx$ 1.4 at 600 K.

An industrially viable TOPCon structure with both ultra-thin SiOx and n+-poly-Si processed by PECVD for p-type c-Si solar cells

We report an industrial compatible tunnel oxide passivated contact (TOPCon) structure on solar-grade p-type c-Si wafer as the rear emitter for high-efficiency solar cells, where the ultrathin silicon oxide (SiOx) is made by plasma-assisted oxidation and the P-doped n-type poly-Si (n+-poly-Si) contact layer by plasma-enhanced chemical vapor deposition (PECVD) of hydrogenated amorphous silicon (a-Si:H) with in-situ doping with PH3 and following the high-temperature annealing. The fabrication processes of SiOx and n+-poly-Si layers are systematically optimized. It is found that the optimized annealing temperature for the crystallization and dopant activation is in the range of 850 °C and 880 °C, which is higher than the similar structure with chemically oxidized SiOx (820 °C). In addition, the samples made with higher PH3/SiH4 doping ratio during the a-Si:H deposition need a lower annealing temperature to reach the similar dopant distribution within the samples made with lower doping ratio but annealed at higher temperature, it means that the optimized annealing temperature decreases with the increase of the PH3/SiH4 doping ratio during the deposition of a-Si:H precursor. The optimized process with post-hydrogenation yields excellent surface passivation on the p-type Si substrate with the implied open-circuit voltage (iVoc) of ∼742 mV, the single-side saturated recombination current density (J0) of ∼3.0 fA/cm2, the contact resistivity (ρc) of ∼2–4 mΩ cm2, and the effective minority carrier lifetime (τeff) of ∼1050 μs (Δn = 1 × 1015 cm-3). With these passivation parameters, a simulation study demonstrates the advantage of rear emitter over the conventional front emitter TOPCon solar cell with ∼22.8% achievable efficiency on solar-grade p-type wafers with current industrial constraints, and ∼24.9% on high quality p-type c-Si wafers with the optimized conditions in R&D laboratories. Our study suggests that the p-type c-Si solar cell with a rear n+-poly-Si TOPCon emitter is a viable structure for high-efficiency solar cell production.

Suppression of Ge-based defects and auto-doping of p-type epitaxial GaAs by employing Al0.3Ga0.7As bi-layer buffer

Development of high quality p-type epitaxial gallium–arsenide (epi-GaAs) film on germanium substrates with sub-nm surface roughness is much sought after for the next generation high speed transistors and optical device applications. In our work, zinc-doped p-type epitaxial GaAs with surface roughness of ∼0.3 nm is grown on germanium (Ge) substrate at 675 °C by employing bi-layer of Al0.3Ga0.7As buffer along with 300 nm thick un-doped GaAs. The structural quality and optical properties of p-type epi-GaAs layer with bi-layer Al0.3Ga0.7As on Ge substrate are examined through photoluminescence and Raman analysis. The presence of Al0.3Ga0.7As bi-layer suppresses Ge-based complex defects and background auto-doping (n-type) into epi-GaAs layer. The metal–oxide–semiconductor (MOS) capacitors are fabricated on p-type epi-GaAs layer by depositing Al2O3 (12 nm) as gate dielectric by using Atomic-layer-deposition (ALD) method. Capacitance-voltage and current-voltage characteristics show significant improvement of interface quality and bulk oxide quality with Al0.3Ga0.7As bi-layer buffer. The capacitance-voltage characteristics reveal that the epi-GaAs layer is p-type in nature with substrate doping of ∼1017 to 1018 cm−3. The frequency dispersion and interface defects are remarkably reduced for the device with bi-layer buffer and thus the introduction of bi-layer Al0.3Ga0.7As is crucial for the developing p-type epi-GaAs based electronic devices.

High-Mobility p-Type and n-Type Copper Nitride Semiconductors by Direct Nitriding Synthesis and In Silico Doping Design.

Thin-film photovoltaics (PV) have emerged as a technology that can meet the growing demands for efficient and low-cost large-scale cells. However, the photoabsorbers currently in use contain expensive or toxic elements, and the difficulty in bipolar doping, particularly in a device structure, requires elaborate optimization of the heterostructures for improving the efficiency. This study shows that bipolar doping with high hole and electron mobilities in copper nitride (Cu3 N), composed solely of earth-abundant and environmentally benign elements, is readily available through a novel gaseous direct nitriding reaction applicable to uniform and large-area deposition. A high-quality undoped Cu3 N film is essentially an n-type semiconductor, while p-type conductivity is realized by interstitial fluorine doping, as predicted using density functional theory calculations and directly proven by atomically resolved imaging. The synthetic methodology for high-quality p-type and n-type films paves the way for the application of Cu3 N as an alternative absorber in thin-film PV.

Recent Advances on p-Type III-Nitride Nanowires by Molecular Beam Epitaxy

p-Type doping represents a key step towards III-nitride (InN, GaN, AlN) optoelectronic devices. In the past, tremendous efforts have been devoted to obtaining high quality p-type III-nitrides, and extraordinary progress has been made in both materials and device aspects. In this article, we intend to discuss a small portion of these processes, focusing on the molecular beam epitaxy (MBE)-grown p-type InN and AlN—two bottleneck material systems that limit the development of III-nitride near-infrared and deep ultraviolet (UV) optoelectronic devices. We will show that by using MBE-grown nanowire structures, the long-lasting p-type doping challenges of InN and AlN can be largely addressed. New aspects of MBE growth of III-nitride nanostructures are also discussed.

Stoichiometric p-type Cu2O thin films prepared by reactive sputtering with facing target

We have investigated the high quality p-type Cu2O thin films produced by the post vacuum annealing process of Cu2O thin films deposited on glass substrates at room temperature by facing target sputtering. As-deposited stoichiometric films show the high Cu2O (111)-axis orientation with the minimum value of electrical resistivity of 17Ωcm. Furthermore, the XRD peaks intensities continuously decrease around the stoichiometric 2θ value of 36.4° with increasing the O2 partial pressure. With the vacuum annealing at 550°C with optimized oxygen ambient, the high quality p-type Cu2O thin film could be obtained. The highest value of Hall mobility μH of 61cm2/Vs is obtained for a vacuum annealed stoichiometric p-type Cu2O thin film. Such high value of μH in the described stoichiometric p-type Cu2O thin film is believed to be due to the minimized oxygen vacancies induced by optimized vacuum annealing of a stoichiometric as-deposited Cu2O thin film.

A Mixture of Ionic Liquid and Ethanol Used for Galvanostatic Electrodeposition of CuInxGa1-xSe2 Thin Films

A mixture of 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF4) and ethanol is used for synthesizing CuInxGa1-xSe2 (CIGS) thin films by one-step electrodeposition. The conductivity and electrochemical windows of the mixtures with different volume ratios of ethanol are studied, and Fourier transform infrared spectroscopy spectra are recorded for investigating the interaction between BMImBF4 and ethanol, which indicates that the cations and anions of the ionic liquid interact with ethanol molecule. The electrochemical behaviors of Cu-In-Ga-Se systems are investigated with different ethanol volume fraction. Quantum chemical calculations and molecular dynamic simulations are introduced to study the electronic properties and orbital information of mixtures and electrochemical behaviors of Cu-In-Ga-Se in the mixture. CIGS thin films are characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy in terms of morphology and composition, and by X-ray diffraction and Raman regarding crystal structure. The results show ethanol content has great influences on the electrochemical behaviors of Cu-In-Ga-Se systems as well as the composition and morphology of CIGS thin films. The deposited CIGS thin films are high crystalline quality p-type semiconductor with a bandgap of 1.28 eV after annealed. The mixture can be a promising candidate in industrial application of ionic liquids for electrodeposition of CIGS thin films, even other metals, alloys and semiconductors.

A High Mobility of p-Type Sno Thin Films Grown By Atomic Layer Deposition for Thin Film Transistors

Oxide semiconductors have attracted great interest as channel materials for use in various emerging electronic applications including transparent and flexible displays, sensors, logic devices, and so on. Great progress has been made in n-type oxide semiconductors for thin film transistors (TFTs), which show superior properties such as high electron mobility and Ion/off ratio. Despite rapid development of n-type oxides, progress in the development of p-type oxides has been delayed. Only a few oxides including SnO, CuO, and NiO have been reported for p-type TFTs, and not yet sufficient for applications. Furthermore, most of the p-type oxides have been fabricated by a reactive sputtering technique, which is not applicable in industry. In this study, we propose atomic layer deposition (ALD) of stable and high quality p-type SnO thin films for p-type TFTs. The SnO films were deposited with dimethylamino-2-methyl-2-propoxy-tin(II) and H2O as Sn and O sources, respectively. The growth of the SnO films was performed in a growth temperature range from 150 to 210 oC. From the XPS analysis, the ALD-grown SnO films are mainly composed of Sn2+ ions and O2- ions, and a peak from Sn4+ ions in the XPS spectra is not observed. As increasing the growth temperature, the Hall mobility increased from 1.26 to 3.8 cm2/Vs and Sn/O atomic ratio of the films approached the stoichiometric value from less unity (O-rich phase). We also fabricated TFTs with the ALD-grown SnO layer to characterize the properties of the p-channel layer in the TFTs. To exclude the influence of environment, we deposited a 15 nm-thick Al2O3 passivation layer on the TFTs by ALD. The field effect mobility increased with increasing the growth temperature, consistent with the change in the Hall mobility. A high field effect mobility of 1.5 cm2/Vs was achieved at a growth temperature of 210 oC. A high Ion/off ratio of ~ 106 was also achieved in the SnO film grown at 210 oC. This is attributed to the formation of dense and stoichiometric SnO films at 210 oC.

Boric acid solution concentration influencing p-type emitter formation in n-type crystalline Si solar cells

Boric acid (BA) is a spin on dopant (BSoD) source which is used to form p+ emitters in n-type c-Si solar cells. High purity boric acid powder (99.99% pure) when mixed with deionized (DI) water can result in high quality p-type emitter with less amount of surface defects. In this work, we have used different concentrations of boric acid solution concentrations to fabricate p-type emitters with sheet resistance values < 90 Ω/□. The corresponding junction depths for the same are less than 500 nm as measured by SIMS analysis. Boron rich layer (BRL), which is considered as detrimental in emitter performance is found to be minimal for BA solution concentration less than 2% and hence useful for p-type emitter formation.

One-step synthesis of p-type GaSe nanoribbons and their excellent performance in photodetectors and phototransistors

High quality p-type GaSe nanoribbons were synthesized and the nanoribbon-based nanodevices reflect an excellent photodetection ability and quadrupled mobility.

Effects of pre-annealed ITO film on the electrical characteristics of high-reflectance Ni/Ag/Ni/Au contacts to p-type GaN

In this study, a Ni/Ag/Ni/Au multilayer with first Ni layer of 0.5nm was first optimized for high reflectivity (92.3%), low specific contact resistance (2.1×10−3Ωcm2) and good attachment strength to p-type GaN. To further decrease the contact resistance, the p-type GaN surface was previously treated with pre-annealed indium-tin-oxide (ITO) film before deposition of the Ni/Ag/Ni/Au multilayer, and resulted in a lower specific contact resistance of 1.9×10−4Ωcm2. The X-ray photoelectron spectroscopy results indicated that Ga 2p core level of the p-type GaN surface with the pre-annealed ITO film had a lower binding energy, leading to a reduction in the contact resistance. Furthermore, GaN-based flip-chip light-emitting diodes (LEDs) with and without the pre-annealed ITO film were fabricated. The average forward voltage of the flip-chip LEDs fabricated with the pre-annealed ITO film is 3.22V at an injection current density of 35A/cm2, which is much lower than that (3.49V) of flip-chip LEDs without the pre-annealed ITO film. These results reveal that the proposed approach is effectively to fabricate high quality p-type contacts toward high power GaN-based LEDs.

Role of vacancies in tuning the electronic properties of Au-MoS2 contact

Understanding the electronic properties between molybdenum disulfide (MoS2) and metal electrodes is vital for the designing and realization of nanoelectronic devices. In this work, influence of intrinsic vacancies in monolayer MoS2 on the electronic structure and electron properties of Au-MoS2 contacts is investigated using first-principles calculations. Upon formation of vacancies in monolayer MoS2, both tunnel barriers and Schottky Barriers between metal Au and monolayer MoS2 are decreased. Perfect Au-MoS2 top contact exhibits physisorption interface with rectifying character, whereas Au-MoS2 contact with Mo-vacancy shows chemisorption interface with Ohmic character. Partial density of states and electron density of defective Au-MoS2 top contacts are much higher than those of perfect one, indicating the lower contact resistance and higher electron injection efficiency of defective Au-MoS2 top contacts. Notably, Mo-vacancy in monolayer MoS2 is beneficial to get high quality p-type Au-MoS2 top contact, whereas S-vacancy in monolayer MoS2 is favorable to achieve high quality n-type Au-MoS2 top contact. Our results provide guidelines for designing and fabrication of novel 2D nanoelectronic devices.

Theoretical study of cesium and oxygen activation processes on GaN (0001) surface

The structure properties and work function of reflection-mode GaN photocathodes are investigated by using first-principles calculation within density-function theory (DFT). Seven different GaN (0001) (1×1) surface models are used in this paper to simulate cesium and oxygen activation process. Before starting the surface models calculations, clean bulk GaN surface is first optimized, when compared with the models before optimization, the correctness of the calculations method is verified. Next, change of work function of different surface models caused by adsorption is calculated and analyzed, the results show that over-cesiuminizd atmosphere is not only benefit for work function declining but also conductive to the formation of negative electron affinity (NEA), the optimal ratio of Cs to O for activation is between 3:1 and 4:1, excess Cs or O modules increase the work function and undermine the photocathode. Then a series of experiments are performed to verify the calculation results. First of all, NEA GaN photocathode activation and evaluation system is established, “yo-yo” activation method is verified. Then, an activation experiment is performed on high quality p-type Mg-doped reflection-mode GaN substrate grown by metal organic chemical vapor deposition (MOCVD), the photocurrent is controlled and monitored by multi-information on-line monitoring system, the results are consistent with our calculation models. Finally, combined with the data provided by Stanford University, schematic energy band variation of the GaN photocathode after only-Cs and Cs/O activations is given. Our result opens the possibility to engineer the activation properties of GaN photocathode.

Atomic layer deposited Al2O3 on high quality p-type epitaxial-GaAs/Ge for advanced III–V/Ge based device application

Development of high quality p-type epitaxial gallium–arsenide (epi-GaAs) on germanium (Ge) with sub-nm surface roughness is much sought after for the next generation high speed transistors application. High quality zinc doped p-type epitaxial GaAs with surface roughness of ~0.87nm was grown on Ge substrates at 675°C. Thin Al0.3Ga0.7As buffer layer and un-doped GaAs of 300nm thick were introduced to suppress the Ge defects and auto-doping into epi-GaAs layer. The material and optical properties of the p-type epi-GaAs/un-doped GaAs/Al0.3Ga0.7As/Ge structures were examined through PL and Raman analysis. The metal–oxide–semiconductor capacitor (MOSC) was fabricated using p-type epi-GaAs layer and atomic-layer-deposited Al2O3 gate dielectric. The effective dielectric constant of the Au/Al2O3/p-epi-GaAs gate-stack is 5.9 and hysteresis voltage of 500mV was observed. The epi-GaAs layer is p-type in nature with doping densities of 5×1017cm−3.

Effect of deposition temperature on transparent conductive properties of γ-CuI film prepared by vacuum thermal evaporation

Copper (I) iodide (CuI) films are grown on glass substrates with a direct vacuum thermal evaporation method, and the effect of substrate temperature on their photoluminescence and transparent conductive properties is discussed. The X-ray diffraction (XRD) measurement identifies the polycrystalline CuI film has γ-phase with (111) preferential growth direction. When the substrate temperature is optimised at 120 °C, the average transmittance is about 90% in the wavelength range of 410–1500 nm. The electrical properties measured by Hall effect show the lowest resistivity of 1.0 × 10−2 Ωcm with hole concentration of 3.0 × 1019 cm−3 and mobility of 25 cm2 V−1s−1. These results indicate that direct thermal deposition is a simple method to grow high quality p-type CuI films.

One-step electrodeposition of CuInxGa1−xSe2 thin films from a mixture system of ionic liquid and ethanol

Synthesizing high crystalline quality p-type semiconductor CIGS thin film with a band gap of 1.41 eV by galvanostatic electrodeposition.

Hole-spin pumping and repumping in ap-type δ-doped InAs quantum dot

We have grown high quality p-type {\delta}-doped InAs quantum dots and have demonstrated coherent spin pumping and repumping of a hole spin in a positively charged quantum dot by means of a single-laser driving scheme under a high magnetic field in the Voigt configuration. Modeling of our system shows excellent qualitative agreement with the experimental findings and further explores the performance of the single-laser scheme for spin pumping and re-pumping.

Pulsed laser deposition of Li–N dual acceptor in p-ZnO:(Li, N) thin film and the p-ZnO:(Li, N)/n-ZnO homojunctions on Si(100)

This article showed the p-type ZnO thin films which were co-doped with different components of Li and N by pulsed laser deposition (PLD) on Si(111) substrates. According to Hall-effect data, the Li-N co-doped ZnO:(Li, N) exhibited stable room-temperature p-type behavior. Combining the XRD, UV-vis transmittance spectrum, and Hall-effect data, the preferable preparation condition was proposed for growing high quality p-type ZnO:(Li, N) film with comparatively low resistivity of 0.09 Ω cm and relatively high carrier concentration of 2.64 × 1017 cm−3, which were obtained at 0.1 at. % lithium composition. Furthermore, compared with the photoluminescence spectrum of ZnO:(Li) with ZnO:(Li, N) thin film, the existence of Li–N dual acceptor, which activated the acceptor in ZnO:(Li, N) thin film, was confirmed. On the basis of these, the p-ZnO:(Li, N)/n-ZnO homojunctions on Si(100) substrate was realized by PLD. All these data proved that Li-N dual acceptor would be effective when activated by PLD doping and this approach was feasible to realize the physical device homojunctions on Si substrate.