Transparent P-type Semiconductor Research Articles

Heavy-ion irradiation assisted modification of p-type transparent CuAlO2 films: Electrical, optical and thermoelectric properties

Heavy-ion (HI) irradiation is a unique approach to induce defects in semiconductor films. The ion irradiation leaves continuous columnar tracks to create various defects and reduce film density, modulating the thermoelectric properties of semiconductor films. As a p-type transparent oxide semiconductor (TOS), the as-synthesized CuAlO2 films were irradiated with different doses of Fe10+ ions at room temperature using the 320 kV High Voltage Platform, and then post-annealed to improve the microstructure and thermoelectric properties. The irradiated CuAlO2 films, with 15 × 1013 ions cm−2, can achieve an electrical conductivity of 0.14 S cm−1, which is about 200 times larger than the unirradiated counterparts. The Seebeck coefficient reaches up to 189.80 and 208.58 μV K−1 at room temperature and 600 K, respectively. Therefore, a high power factor (PF) of 9.15 μW m−1K−2 is rendered by the irradiated CuAlO2 films, whereas the unirradiated films are not detected in the given measurement range. The improved thermoelectric performance is mainly due to the increased copper vacancies in irradiated films without significantly reducing the crystallinity. The current work presents a promising strategy to improve the thermoelectric performance of semiconductor films.

A P-type mid-infrared transparent semiconductor LaSe2 film with small hole effective mass and high carrier concentration

P-type transparent conductive materials (TCMs) are urgently needed in the development of photoelectric devices. In particular, the P-type TCMs that can be applied in the mid-infrared range are even rarer due to the conflict between the transparent range and the conductivity of materials. In this work, a P-type mid-infrared transparent conductive LaSe2 film is obtained by a two-step method combining the RF sputtering and a selenized annealing process. The crystal structure of the film has been confirmed by x-ray diffraction and Raman spectrum analysis. According to the Hall effect measurement results, the LaSe2 film has a higher conductivity (about 3.6 S/cm) than that of traditional P-type mid-infrared TCMs, which is attributed to its ten times higher carrier concentration (about 1019 cm−3) and a much smaller hole effective mass (about 0.34 me) compared to the conventional P-type mid-infrared TCMs. The transmittance (about 75%) is at the same level as that of the traditional P-type mid-infrared TCMs. In a sense, the LaSe2 is a promising candidate material for the development of mid-infrared photoelectric devices.

Beryllium sulfur doped with N, Li and Na: Promising p-type transparent semiconductor

The properties for group IA and VA atoms doped BeS are studied by using the first-principles method. Our studies show BeS is a transparent semiconductor. The visible light transmittances could reach 80.0 %, as the thickness increases to 60.0 nm. The holes effective mass along the Г-X and Г-L directions are 0.56 and 1.34 m0 (m0 is electron’s static mass). The defective behaviors for group IA and VA atoms in BeS show that N substituting S, together with the Li and Na substituting Be are shallow acceptors, and the corresponding ionization energy levels ε(0/-), compared to the valence band maximum, are 0.166, 0.177 and 0.25 eV, respectively. Formation energies imply under S-rich condition, NS, LiBe and NaBe defects can be realized experimentally by using the equilibrium growth conditions, while the detrimental hole killers, such as, VS, Bei, Nint, Liint and Naint would be inhibited as samples fabrication. These properties indicate N, Li and Na doped BeS may offer new opportunities in transparent electronics and optoelectronic applications.

Switching the electrical characteristics of TiO2 from n-type to p-type by ion implantation

For many applications, as for example tandem dye-sensitized solar cells (DSSCs), the development of transparent p-type semiconductor with good charge transport properties is crucial. In this work, a nitrogen-doped TiO2 material is transformed by ion implantation into an efficient hole transport layer that could reduce the electron-hole recombination processes in the devices. Theoretical calculations allowed to demonstrate that the position of nitrogen species as well as their respective ratio impact the optical and electrical properties of N-doped TiO2 materials. The chemical composition was therefore tuned by the ion implantation parameters, achieving a high transparency in the UV–visible region while generating delocalized states near the top of the valence band that do not act as traps. In terms of electrical properties, beyond the possibility to tune the electrical behavior of TiO2 from n-type to p-type upon nitrogen doping, we succeed to increase the conductivity by a higher electron mobility without change in their density, which is of prime interest for charge transport application.

Engineering Copper Iodide (CuI) for Multifunctional p-Type Transparent Semiconductors and Conductors.

Developing transparent p‐type semiconductors and conductors has attracted significant interest in both academia and industry because metal oxides only show efficient n‐type characteristics at room temperature. Among the different candidates, copper iodide (CuI) is one of the most promising p‐type materials because of its widely adjustable conductivity from transparent electrodes to semiconducting layers in transistors. CuI can form thin films with high transparency in the visible light region using various low‐temperature deposition techniques. This progress report aims to provide a basic understanding of CuI‐based materials and recent progress in the development of various devices. The first section provides a brief introduction to CuI with respect to electronic structure, defect states, charge transport physics, and overviews the CuI film deposition methods. The material design concepts through doping/alloying approaches to adjust the optoelectrical properties are also discussed in the first section. The following section presents recent advances in state‐of‐the‐art CuI‐based devices, including transparent electrodes, thermoelectric devices, p–n diodes, p‐channel transistors, light emitting diodes, and solar cells. In conclusion, current challenges and perspective opportunities are highlighted.

Enhanced Electrical Properties and Stability of P-Type Conduction in ZnO Transparent Semiconductor Thin Films by Co-Doping Ga and N

P-type ZnO transparent semiconductor thin films were prepared on glass substrates by the sol-gel spin-coating process with N doping and Ga–N co-doping. Comparative studies of the microstructural features, optical properties, and electrical characteristics of ZnO, N-doped ZnO (ZnO:N), and Ga–N co-doped ZnO (ZnO:Ga–N) thin films are reported in this paper. Each as-coated sol-gel film was preheated at 300 °C for 10 min in air and then annealed at 500 °C for 1 h in oxygen ambient. X-ray diffraction (XRD) examination confirmed that these ZnO-based thin films had a polycrystalline nature and an entirely wurtzite structure. The incorporation of N and Ga–N into ZnO thin films obviously refined the microstructures, reduced surface roughness, and enhanced the transparency in the visible range. X-ray photoelectron spectroscopy (XPS) analysis confirmed the incorporation of N and Ga–N into the ZnO:N and ZnO:Ga–N thin films, respectively. The room temperature PL spectra exhibited a prominent peak and a broad band, which corresponded to the near-band edge emission and deep-level emission. Hall measurement revealed that the ZnO semiconductor thin films were converted from n-type to p-type after incorporation of N into ZnO nanocrystals, and they had a mean hole concentration of 1.83 × 1015 cm−3 and a mean resistivity of 385.4 Ω·cm. In addition, the Ga–N co-doped ZnO thin film showed good p-type conductivity with a hole concentration approaching 4.0 × 1017 cm−3 and a low resistivity of 5.09 Ω·cm. The Ga–N co-doped thin films showed relatively stable p-type conduction (>three weeks) compared with the N-doped thin films.

Photoluminescence properties and defects in CuBr1-xIx thin films and their dependence on halogen ratio

The dependence of photoluminescence (PL) from a thin film transparent p-type semiconductor of CuBr1-xIx (x ​= ​0.0–1.0) on the temperature and excitation intensity was investigated. The transmittance spectra showed that the band gap energy varied with x. All samples showed PL at around 2.9 ​eV, but the actual position showed a dependence on the band gap energy. This peak contained four components (P1–P4), of which P1 had the highest energy and P2 had the second highest energy. The origin of the P1 and P2 components were concluded to be exciton recombination and the transition between the Cu vacancy (VCu) level and the conduction band minimum, respectively. The exciton binding energy and VCu level were estimated from the temperature dependence of the PL. For all values of x, the estimated VCu level was ca. 50 ​meV.

High-performance p-channel transistors with transparent Zn doped-CuI

‘Ideal’ transparent p-type semiconductors are required for the integration of high-performance thin-film transistors (TFTs) and circuits. Although CuI has recently attracted attention owing to its excellent opto-electrical properties, solution processability, and low-temperature synthesis, the uncontrolled copper vacancy generation and subsequent excessive hole doping hinder its use as a semiconductor material in TFT devices. In this study, we propose a doping approach through soft chemical solution process and transparent p-type Zn-doped CuI semiconductor for high-performance TFTs and circuits. The optimised TFTs annealed at 80 °C exhibit a high hole mobility of over 5 cm2 V−1 s−1 and high on/off current ratio of ~107 with good operational stability and reproducibility. The CuI:Zn semiconductors show intrinsic advantages for next-generation TFT applications and wider applications in optoelectronics and energy conversion/storage devices. This study paves the way for the realisation of transparent, flexible, and large-area integrated circuits combined with n-type metal-oxide semiconductor.

A New Highly Conductive Direct Gap p-Type Semiconductor La1-xYxCuOS for Dual Applications: Transparent Electronics and Thermoelectricity.

The absence of a high-performance p-type transparent semiconductor still remains as a roadblock to the development of future generation optoelectronics. Here, a highly conducting p-type transparent semiconductor based on Y incorporated LaCuOS oxychalcogenide is achieved for the first time, and the maximum Y substitution to obtain a single phase is found to be 25%. By enhancing both the hole mobility and concentration of the LaCuOS phase, Y-substituted oxychalcogenide single-phase La0.75Y0.25CuOS exhibits an outstanding p-type conductivity of 89.3 S·cm-1 with high optical transparency, which is the highest among all transparent oxychalcogenides with a band gap above 3 eV reported so far. The structural, electronic, and optical as well as the thermoelectric properties of La1-xYxCuOS with a different Y substitution level are investigated, and the power factor was greatly enhanced to 4.322 μW m-1 K-2 after Y substitution. The highly performing diode based on a p-type La0.75Y0.25CuOS thin film and n-type Al-doped ZnO heterojunction with a high rectifying ratio of 300 is demonstrated, indicating its promising aspect for the next generation of invisible electronics and optoelectronics.

Preparation of CuCl1−xIx thin films by spin coating

CuCl1−XIX thin films were prepared to create variable band gap, transparent p-type semiconductor without use of vacuum processes, by employing spin coating. The X-ray diffraction analysis spectra of the fabricated CuCl1−XIX thin films revealed the dominant CuCl1−XIX peak shift to a higher angle with decreasing mixing ratio X. In the compositional analysis, the dependence of the film composition X on the solution composition x was confirmed. The exciton absorption band for each composition was observed from 370 to 420 nm, revealing that the absorption wavelength varied with X. The ionization potential was obtained by photo yield spectroscopy to study the energy band structure of CuCl1−XIX. The CuCl1−XIX ionization potential increases with increases in X. On the basis of the present results, which suggests that the valence band maximum for CuCl1−XIX depends on the composition, an energy band structure was proposed for this material.

Research progress of tin oxide-based thin films and thin-film transistors prepared by sol-gel method

Transparent conductive oxide (TCO) films and transparent oxide semiconductor (TOS) films have been widely adopted in solar cells, flat panel displays, smart windows, and transparent flexible electronic devices due to their advantages of high transparency and good conductivity and so on. Most of TCO and TOS films are mainly derived from indium oxide, zinc oxide and tin oxide. Among these materials, the In element is toxic, rare and expensive for indium oxide film, which will cause environmental pollution; zinc oxide film is sensitive to acid or alkali etchants, resulting in a poor formation of film patterning; tin oxide film is not only non-toxic, eco-friendly, and cheap but also has good electrical properties and strong chemical stability. Thus, tin oxide has a great potential for developing the TCO and TOS films. At present, the film is prepared mainly by the vacuum deposition technique. The drawbacks of this technique are complex and expensive equipment system, high energy consumption, complicated process and high-cost production. However, compared with the vacuum deposition technique, the sol-gel method has attracted extensive attention because of its virtues such as simple process and low cost. In this paper, we review the development status and trend of TCO and TOS films. First, the structural characteristics, conductive mechanism, element doping theory and carrier scattering mechanism of tin oxide thin films are introduced. Then the principle of sol-gel method and correlative film fabrication techniques are illustrated. Subsequently, the application and development of tin oxide-based thin films prepared by sol-gel method in n-type transparent conductive films, thin-film transistors and p-type semiconductor films in recent years are described. Finally, current problems and future research directions are also pointed out.

Effect of swift heavy 86Kr30+ ions irradiation on optical and electrical properties of p-type transparent Ni-doped CuAlO2 films

Swift heavy ion (SHI) irradiation is an effective approach to modulate the structure, optical and electrical properties of semiconductors. Herein, we present the influence of 86Kr30+ ions irradiation on optical and electrical properties of p-type transparent oxide semiconductor Ni-doped CuAlO2 films prepared by sol–gel method. The results reveal that Ni-doping inhibits the amorphization of CuAlO2 films during swift heavy ions irradiation and decreases the surface roughness of SHI-irradiated Ni-doped CuAlO2 films. However, SHI-irradiated Ni-doped CuAlO2 films exhibit higher optical transmittance (74%) and lower electrical resistivity (11.5 Ω cm), which corresponds to a decrease of two orders of magnitude due to the generation of a large number of carriers. In addition, SHI-irradiated Ni-doped CuAlO2 film renders photosensitive behavior and a reduced electrical resistivity of 7.4 Ω cm is achieved under UV illumination. The superior optical and electrical properties of SHI-irradiated Ni-doped CuAlO2 films can be ascribed to the thermal spike effect of high-energy ions.

Tailoring the Hole Mobility in SnO Films by Modulating the Growth Thermodynamics and Kinetics

Obtaining semiconducting properties that meet practical standards for p-type transparent oxide semiconductors is challenging due to the balance between the defects that generate hole and electron c...

Recent Research Trends in Point Defects in Copper Iodide Semiconductors

Copper iodide is a transparent p-type semiconductor that can be applied in thin-film transistors, transparent conductors, and light-emitting devices. Point defects affect the semiconductor properties of copper iodide. Therefore, many researchers have attempted to reveal the properties of point defects in copper iodide. A typical optical property related to point defects is photoluminescence (PL). PL peaks (430 nm and 700 nm) derived from defects have been reported for single-crystalline copper iodide. Density functional theory (DFT) studies reveal that the most stable defect species is the copper vacancy (VCu). These studies report that PL energies and defect species can be associated using experimental and DFT analyses. Researchers have also introduced defects into copper iodide single crystals or thin films artificially by controlling the annealing atmosphere and observed the relationship between the PL or absorption energy and Cu/I ratio. A comparison of this result with DFT results revealed that the photoactive defects were copper vacancies (VCu), iodine vacancies (VI), and iodine ions substituted at copper sites (ICu). Elucidation of the origin of fluorescence and coloration has enabled active control of optical properties via synthesis conditions. However, more drastic control of optical or electrical properties by doping is required for fabrication of actual devices. Some DFT studies on chalcogen doping have been reported; however, more theoretical and experimental studies are required.

Optical Studies of RF Sputtered CuInO2 Thin Films

N type transparent conducting oxide semiconductors have been researched extensively in the past. P-type transparent semiconductors have been comparatively researched lesser. In order to advance in the field of transparent p-n junction devices, more and more researches are being done on p-type transparent semiconductors. CuInO2 is one of the p-type transparent semiconductor that has the prospects of being used extensively in transparent p-n junction devices. CuInO2 (50:50 of Cu2O: In2O3) thin films were RF sputter deposited onto glass slides. Optical transmission studies were performed on these thin films to extract the band gap. The deposition studies were also performed. The sputtered films were subsequently post annealed in different temperatures and different ambient conditions and their respective optical transmissions were recorded.

Optical properties of single crystalline copper iodide with native defects: Experimental and density functional theoretical investigation

Copper iodide (CuI) is an attractive transparent p-type semiconductor, and we investigated the relationship between the optical property and native defects in CuI using experimental and theoretical studies. To exclude neither surface impurity nor interface strain, we used well-defined CuI single crystals with native defects, i.e., Cu-rich CuI and I-rich CuI, as well as highly pure CuI, which were prepared by post-annealing treatment of the CuI single crystal under controlled atmosphere. The optical absorption and photoluminescence (PL) properties of these samples were then carefully evaluated. Consequently, two absorption signals (AB1: 2.9 eV, AB2: 2.7 eV) and two PL peaks (PL1: 2.9 eV, PL2: 1.8 eV) were observed. The AB1, AB2, and PL1 signals were obvious under I-rich conditions, whereas the PL2 signal was dominant in the Cu-rich sample. To discuss the origin of these absorption and PL signals, we calculated the absorption and emission energies of defects in CuI using the density function theory (DFT). As a result, AB1 and PL1 are assigned to the transition and recombination between copper vacancy (VCu) and conduction band, while PL2 is assigned to the recombination from the iodine vacancy (VI) to the valence band. Most interestingly, AB2 is presumed to be due to the transition from the valence band to antisites of iodine substituted for copper (ICu), which can be reasonably explained by the off-center model of substituted iodine ions. This work will contribute to developing and understanding opto-electrical devices using CuI.

Improvement of the hole mobility of SnO epitaxial films grown by pulsed laser deposition

Stannous oxide, SnO, is a promising material for practical applications as a p-type transparent oxide semiconductor. The hole mobility of SnO epitaxial films grown by pulsed laser deposition can be improved by reducing the growth temperature.

Enhancing the intrinsic p-type conductivity of the ultra-wide bandgap Ga2O3 semiconductor

Strongly compensated Ga2O3 is shown to be an intrinsic (or native) p-type conductor with the largest bandgap for any reported p-type transparent semiconductor oxide which may shift the frontiers in fields such as power electronics and photonics.

Computational acceleration of prospective dopant discovery in cuprous iodide.

The zinc blende (γ) phase of copper iodide holds the record hole conductivity for intrinsic transparent p-type semiconductors. In this work, we employ a high-throughput approach to systematically explore strategies for enhancing γ-CuI further by impurity incorporation. Our objectives are not only to find a practical approach to increase the hole conductivity in CuI thin films, but also to explore the possibility for ambivalent doping. In total 64 chemical elements were investigated as possible substitutionals on either the copper or the iodine site. All chalcogen elements were found to display acceptor character when substituting iodine, with sulfur and selenium significantly enhancing carrier concentrations produced by the native VCu defects under conditions most favorable for impurity incorporation. Furthermore, eight impurities suitable for n-type doping were discovered. Unfortunately, our work also reveals that donor doping is hindered by compensating native defects, making ambipolar doping unlikely. Finally, we investigated how the presence of impurities influences the optical properties. In the majority of the interesting cases, we found no deep states in the band-gap, showing that CuI remains transparent upon doping.

Carrier Generation in p-Type Wide-Gap Oxide: SnNb2O6 Foordite

Wide-gap oxides with their valence band maximum (VBM) composed of s orbitals are essential for realizing practical p-type transparent oxide semiconductors. We prepared a new p-type wide-gap oxide, SnNb2O6 foordite, with its VBM composed of Sn 5s orbitals. To discuss carrier generation, we prepared both p-type and n-type SnNb2O6 by controlling the annealing conditions. The carrier mobility and density were 3.8 × 10–1 cm2 V–1 s–1 and 3.7 × 1018 cm–3, respectively, for the p-type sample and 9.9 cm2 V–1 s–1 and 7.5 × 1015 cm–3, respectively, for the n-type sample. The crystal structure of SnNb2O6 foordite consists of two types of alternating layers, Sn and Nb2O6 octahedra, where three nonequivalent oxygen sites exist. Six oxygens in the chemical formula of SnNb2O6 are distributed at the three sites in pairs, where the oxygens in three nonequivalent sites were named O1–O3. Hole and electron carriers were considered to be generated by Sn4+-on-Nb5+ substitutional defects (SnNb′) and oxygen vacancies of O1 and O2...