Conductivity Type Conversion Research Articles

Conduction-type conversion in Ni(OH)2 by intercalation of eosin Y

AbstractNickel hydroxide (Ni(OH)2) is one of the wide bandgap semiconductors. By controlling its conduction type, Ni(OH)2 could be used as a semiconductor material in various applications. Since Ni(OH)2 is a layered material, anions are intercalated into the interlayer spaces. Anion intercalation can be a potential impurity doping technique for Ni(OH)2 films. In this study, we investigated the conduction type of Ni(OH)2 intercalated with eosin Y. Ni(OH)2 films formed by electrochemical deposition were n-type. After the intercalation of eosin Y, the Ni(OH)2 films showed a p-type photocurrent response in photoelectrochemical measurements. The conduction type of the films was changed from n-type to p-type by the intercalation of eosin Y. In addition, the p-type Ni(OH)2 films were used to form heterojunctions. The n-type ZnO/p-type Ni(OH)2 heterojunction diode exhibited a rectifying behavior. Graphical Abstract

Non-amphoteric N-type doping with Sn of GaAs(631) layers grown by molecular beam epitaxy

The Sn-doping effects on the electrical conduction and optical properties of GaAs(631)A epilayers grown by molecular beam epitaxy were investigated. We found that the conduction type conversion, frequently observed in the doping of layers grown on high-index substrates, is avoided when tin-doping is implemented. The maximum free-carrier concentration (n) obtained in GaAs(631):Sn was 2 × 1019 cm−3, an order of magnitude higher than previously reported for GaAs(631):Si, and within the same order of magnitude for the growth of GaAs(100):Si. The electron mobility was suitable for many optoelectronic applications. Raman spectroscopy showed low lattice disorder in (631) oriented samples, compared with singular (100) samples. The photoluminescence characterization of the samples revealed the blueshift of the optical transitions close to E0 associated with the Moss–Burstein effect for Sn doping. Photoreflectance spectroscopy was used to study the doping properties at the critical points E1 and E1 + Δ1, where the major affectation with n was perceived in the broadening parameter Γ.

Sn-guided self-grown Ge stripes banded by GeSn Nanowires: Formation mechanism and electric-field-induced switching from p- to n-type conduction

The formation of GeSn nanostructures catalyzed by Sn surface droplets during the growth of Ge1-xSnx/Ge/Si(001) heterostructures provide a promising strategy for the growth of high-quality Sn-containing group-IV alloys. The droplet formation is favored by Sn segregation at dislocation cores and diffusion of Sn towards the sample surface. Subsequent Sn droplet motion along 〈110〉 crystallographic directions result in self-assembled Ge stripes along the droplet’s path. A novel phenomenon is observed, for which Sn-rich GeSn nanowires (NWs) were periodically formed on top of Ge(Sn) stripes. While the front edge of the liquid Sn droplet is continuously moving and dissolving the Ge1-xSnx epilayer, the phenomenon of NW periodicity is explained by discrete jumping of the back edge of the droplet resulting in redeposition of material forming the NWs. It is also demonstrated that sn-induced phase separation of metastable Ge1-xSnx epilayers leads to carrier redistribution and an electric-field-induced conductivity type conversion from p- to n-type in the Ge(Sn) stripes. These results advance our understanding of the Sn segregation and phase separation mechanism for Ge1-xSnx epilayers at relatively low temperature (≥230 °C). This study could pave the way for understanding the droplet epitaxy synthesis of Sn-rich GeSn nanostructures generating emergent functionalities of GeSn-based nanodevices.

Nanostructured Sb2Te3 films composited with Bi2S3 for p–n conduction type conversion

The crystallization of p-type Sb2Te3 material can be tuned deterministically through compositing with n-type Bi2S3. The underlying changes in conduction from p-type to n-type are due to the crystallization changes induced by the composited Bi2S3 and the simultaneous changes in crystalline phase type. Bi2S3 nanoprecipitate formation and crystallization transition could effectively stimulate the p–n conduction transition. Upon annealing, pure Sb2Te3 partially crystallizes from the as-deposited state, which exhibits continuous crystallization during annealing. The formation of the p-type Sb2Te3 phase and the Sb2O3 phase in pure Sb2Te3 films through oxidation is significantly suppressed through compositing with excess Bi2S3. Moreover, the crystallization temperatures of the Sb2Te3–Bi2S3 films exceed 200 ℃, and the Seebeck coefficients and carrier concentrations of the samples are larger than those of pure Sb2Te3. The X-ray diffraction and Raman spectroscopy characterization of the crystalline thin films reveals a local change of the bonding arrangement around Sb atoms during crystallization. Our results suggest that Sb2Te3–Bi2S3 can serve as a promising candidate for thermoelectric applications based on n-type conduction.

Pressure-Induced Structural Phase Transition, Anomalous Insulator-to-Metal Transition, and n-p Conduction-Type Switching in Defective, NiAs-Type Cr1-δTe.

Cr1-δTe, as a unique series of defective compounds with a NiAs-type structure and periodic metal vacancies, has attracted intensive research interest because of its diversity in structure and property dependent on the tunable stoichiometric ratio. Another feature of these compounds is their ability to switch between NiAs- and MnP-type structures, in which there often exist composition-, temperature-, or pressure-induced phase transitions accompanied by intriguing physical property switching. Herein, we report the syntheses of a series of Cr1-δTe compounds with similar compositions but distinct crystal structures, their phase transitions, anomalous transport, and photoelectric conduction behaviors under high pressure (HP). For the three Cr1-δTe compounds with δ = 0, 0.25, 0.375, CrTe undergoes pressure-induced NiAs-to-MnP phase transition at around 15 GPa, while Cr3Te4 and Cr5Te8 undergo isostructural phase transitions at around 12 and 11 GPa, respectively. Electrical transport measurements indicate anomalous conduction behaviors: CrTe undergoes a semiconductor-to-metal transition at around 24 GPa, while Cr3Te4 and Cr5Te8 show unexpected metal-semiconductor-metal transitions sequentially upon compression. Besides, CrTe and Cr5Te8 exhibit pressure-induced n-p conduction-type switching at around 9 and 3 GPa, respectively, while Cr3Te4 shows p-type conductivity in the full pressure range. Local structure analyses based on in situ HP Raman spectra are performed to understand the structure and property evolutions of Cr1-δTe under HP. Defective transition-metal chalcogenides with pressure-induced NiAs-to-MnP phase transition and conduction-type conversion provide a potential platform for the rational design of photoelectric conversion devices.

Solution growth of chalcopyrite Cu(In1−x Ga x )Se2 single crystals for high open-circuit voltage photovoltaic device

Abstract I–III–VI2 Chalcopyrite Cu(In1−x Ga x )Se2 (CIGS) has attracted attention as absorbing layer in photovoltaic (PV) device. In this study, we investigated the fundamental properties of CIGS single crystals, and fabricated single crystal-based PV device. CIGS single crystals without secondary phase were successfully grown by In-solvent traveling heater method (THM). The conversion of conduction type from n- to p-type can be observed above 0.3 of Ga ratio x because of high acceptor defect concentration. PV device based on high-quality CIGS bulk single crystal demonstrates high open-circuit voltage of 0.765 V with the efficiency of 12.6%.

Influence of Magnesium Doping on the Photocatalytic and Antibacterial Properties of Hematite Nanostructures

Herein, the effect of magnesium doping on hematite nanostructures prepared by a simple and cost‐effective electrochemical method is reported. Photocatalytic and antibacterial studies on the undoped and doped samples suggest improved performance for the Mg‐doped samples. Structural studies using X‐ray diffraction, Raman spectroscopy, and X‐ray photoelectron spectroscopy (XPS) in combination with field‐emission scanning electron microscopy for surface morphology confirm the Mg presence in the nanostructured hematite phase of iron oxide. Analyses of the valence band (VB) XPS spectra along with optical reflectance spectra indicate a shift in VB edge, characteristic of a conductivity type conversion from n‐type in hematite to p‐type in Mg‐doped hematite. The room temperature electrical conductivity is increased by three orders, and the optical bandgap is reduced by around 0.08 eV for moderately doped hematite nanostructures.

Conductivity-Type Conversion in Self-Assembled GeSn Stripes on Ge/Si(100) under Electric Field

We report on the electronic properties of self-assembled Ge99Sn1 stripes surrounded by inhomogeneous Ge96.6Sn3.4 area resulting from the segregation and migration of Sn droplets on Ge89.5Sn10.5/Ge/Si(100). The sample with microscale patterns was characterized at the nanoscale by a combination of techniques including X-ray diffraction, Raman spectroscopy, and scanning probe microscopy. Kelvin probe force microscopy (KPFM) nanoscale maps of the local work function show a spatial inhomogeneity up to 200 meV, which is explained by the band bending induced by holes trapped at the surface states of the Sn droplets. The scanning capacitance microscopy (SCM) of the local charge carrier density shows the dominant p-type conductivity with lateral variation in the hole-density by 1 order of magnitude. The microscale patterns are depleted by holes, and we experimentally revealed an electric-field-induced conductivity-type conversion from p to n in a self-assembled GeSn stripe. Finally, we presented a model and calculations that support the described above experimentally observed phenomena. This work explicitly provides an understanding of the electronic properties of the GeSn micrometer-scale stripes that is important for the implementation of the GeSn in photonic, optoelectronic, electronic, and energy storage devices.

Multiple Long Wavelength Infrared MOCVD Grown HgCdTe Photodetectors for High Temperature Conditions

This paper presents large area multiple photodetectors of the MOCVD grown HgCdTe heterostructures for operation at temperatures of (200-300)K in the long wavelength infrared range. Conventional long wavelength photovoltaic detectors operating at higher temperatures suffer from low dynamic resistance and multiple photodetectors idea solves this problem. Particular experimental steps are demonstrated starting from MOCVD technology, through etching, angled ion milling, angled contact metal deposition, assembly and electro-optical measurements. MOCVD technique with wide range of composition and donor/acceptor doping and without post growth annealing provides HgCdTe heterostructures for uncooled multiple detectors. CdTe buffer layer deposition allows HgCdTe heterostructure growth on GaAs substrates. Angled ion Ar <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> milling optimal selection parameters is crucial for proper junction formation and conductivity type conversion. Theoretical modelling using APSYS platform supports designing of the detector's structures. Presented technology enable to fabricate large area (4 × 4mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) multiple photodetectors with detectivity D* exceeding 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cmHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 10.6 μm and room temperature operation useful for many applications.

Towards the Modeling of Impurity-Related Defects in Irradiated n-Type Germanium: a Challenge to Theory

Electrical measurements on heavily doped n-type germanium subjected to gamma-irradiation show that the features of impurity-related defect formation before n–p conversion of conductivity type are the same as those previously observed in lightly and moderately doped materials, thus extending the range of doping from ≈1014 to ≈1016 cm–3. It is clear now that the presently adopted model of the dominant impurity-related defects as simple vacancy-impurity pairs in irradiated n-Ge, in analogy to such defects reliably identified in irradiated n-Si, appears to be inconsistent with the experimental information collected so far. As a consequence, the impurity diffusion simulations in heavily doped Ge based on this model need to be reconsidered. The requirements to be met while modeling impurity-related defects in irradiated n-Ge in accordance with the reliable experimental data are established.

Electrical conductivity inversion for Nb2O5 nanostructure thin films at different temperatures

The effect of treatment temperature on structural, morphological, and electrical properties of Nb2O5 thin films using the precipitation method is presented in this work. Clear enhancements, such as decreased stress and dislocation density values, are recognized in structural properties after heat treatment. AFM result shows increased average grain size and RMS of the prepared thin film with treatment temperature from 87.87 °C to 110.97 °C and rising temperature from 25 °C to 600 °C. Conductivity type conversion from n- to p-type is observed when the heat treatment is increased from 600 °C to 700 °C based on Hall effect measurement results.

Robustness of ferromagnetism in (In,Fe)Sb diluted magnetic semiconductor to variation of charge carrier concentration

The influence of He+ ion irradiation on the transport and magnetic properties of epitaxial layers of a diluted magnetic semiconductor (DMS) (In,Fe)Sb, a two-phase (In,Fe)Sb composite and a nominally undoped InSb semiconductor has been investigated. In all layers, a conductivity type conversion from the initial n-type to the ptype has been found. The ion fluence at which the conversion occurs depends on the Fe concentration in the InSb matrix. Magnetotransport properties of the two-phase (In,Fe)Sb layer are strongly affected by ferromagnetic Fe inclusions. An influence of the number of electrically active radiation defects on the magnetic properties of the single-phase In0.75Fe0.25Sb DMS has been found. At the same time, the results show that the magnetic properties of the In0.75Fe0.25Sb DMS are quite resistant to significant changes of the charge carrier concentration and the Fermi level position. The results confirm a weak interrelation between the ferromagnetism and the charge carrier concentration in (In,Fe)Sb.

Effects of Nitrogen Partial Pressure Ratio and Anneal Temperature on the Properties of Al–N Co-Doped ZnO Thin Films

The authors report the conversion of conduction type from n-type to p-type in the Al–N co-doped ZnO thin films by using thermal annealing treatment under argon atmosphere. The samples were deposited on fused silica by radio frequency magnetron sputtering. X-ray diffraction measurements showed that ZnO thin films have (002)-preferred orientation and the lattice constant decreases with the increase of nitrogen partial pressure. The average optical transmittance of these films is over 80%. The hole density is around 1.58 × 1017 cm−3 with an annealing temperature of 700°C. After exposing the samples in air for 1 year, the conduction type remains p-type with only a slight decrease of hole density, which indicates that the p-type ZnO with Al–N co-dopants has good electrical stability.

N-Type Conductivity of Cu2O Thin Film Prepared in Basic Aqueous Solution Under Hydrothermal Conditions

We report for the first time in situ hydrothermal synthesis of n-type Cu2O thin film using strong alkaline solution. The use of copper foil as substrate and precursor material, low synthesis temperature and short reaction time represent the arguments of a new, simple, inexpensive and high field synthesis method for the preparation of n-type Cu2O thin film. The donor concentration of n-type Cu2O thin film obtained at 2 h of reaction time has increased two orders of magnitude than previous reported values. We have demonstrated n-type conduction in Cu2O thin film prepared in strong alkaline solution, in the contradiction with the previous works. Based on experimental results, the synthesis mechanism and the origin of n-type photo-responsive behavior of Cu2O thin film were discussed. We have proposed that the unexpected n-type character could be explained by H doping of Cu2O thin film in during of the hydrothermal synthesis that caused the p-to-n conductivity-type conversion. Also, this work raises new questions about the origin of n-type conduction in Cu2O thin film, the influence of the synthesis method on the nature of the intrinsic defects and the electrical conduction behavior.

N-Type conductivity of CuO thin films by metal doping

Due to its unique electrical and optical properties, copper (II) oxide (CuO) potentially has a wide variety of applications. It is commonly known that CuO has p-type conductivity; however, we report observations of n-type conductivity in thin CuO films by metal doping for the first time. We achieved n-type electrical conductivity in CuO films with cobalt (Co) doping. Undoped and Co-doped CuO thin films were fabricated using a spin coating technique. Electrical parameters, specifically, the charge carrier concentration, sheet resistance, and conductivity type were investigated using a van der Pauw Hall measurement system. By 3 per cent of the cobalt doping conductivity type conversion was observed. The effects of metal doping on the width of the optical band gap were investigated using ultraviolet-visible spectrometry over the wavelength range of 300–1100 nm. The optical band gaps were found to be 1.43, 1.44, 1.44, 1.42 eV for un-doped, 2, 4 and 6% Co doped CuO thin films, respectively. The influence of different concentration ratio on the growth of CuO films was investigated using XRD. Microstrain (e), crystalline size (D) and dislocation density (δ) for all orientations were calculated from XRD analysis.

Annealing induced p-type conversion and substrate dependent effect of n-ZnO/p-Si heterostructure

This paper reports the conductivity type conversion of ZnO nanorod thin film by annealing. The n-type conductivity of hydrothermally prepared ZnO nanorods was changed to p-type ZnO through thermal treatment in air ambient without doping process. The ZnO nanorod films were grown on p-Si (111) and p+-Si (100) substrates by hydrothermal method. SEM and XRD measurements showed the excellent crystalline quality and uniform morphology of the grown ZnO nanorod films. Furthermore, substrate and annealing temperature-dependent I-V responses of the films were also studied. A Schottky diode type behavior was shown by ZnO NRs grown on low resistive p-type silicon with a reasonable photoconversion efficiency.

Vertically Stackable One-Dimensional p-n ZnO Homojunction Architectures for UV Sensing/Energy Harvesting Applications

For wide-ranging applications in nanoscale optoelectronic and piezoelectric energy harvesting devices, one-dimensional ZnO nano-architecture and single crystalline doped ZnO having n-/p-type conduction are essential. Herein, catalyst-free ZnO sheet-like nanorods (SLNR) p-n homojunction in which the Lithium (Li) served as p-dopants and intrinsically n-type ZnO, respectively, have been synthesized by a controlled in-situ doping process via hydrothermal synthesis for fabricating efficient ultraviolet UV detectable photonic devices. In addition, a comprehensive investigation was carried out on Li-doped ZnO SLNRs to control the amphoteric electrical behavior of Li in ZnO host lattice. In such cases, Li occupies octahedral sites (Lii O) in the empty cages of the ZnO wurtzite structure and subsequently acts a donor because of the low formation energy, thereby, maintaining or improving the initial n-type behavior of the material. In contrast, the p-type doping by Li atoms occupying Zn site (LiZn) along the growth direction has been achieved by proper thermal activation energy. Further, to obtain n-/p- ZnO nanorods architecture and their vertically stacked p-n homojunctions, the nanorod diameters and morphologies of the ZnO SLNRs were adjusted dramatically by manipulating precursor concentration and growth kinetics. The well-aligned and clean interface between n-/p-ZnO SLNRs could enhance the electron-hole pair generation, transport, separation, thus improved the performance of the homojunction devices. The ZnO p-n homojunction structures have been successfully attained by continuous multi-step solution growth, representing the well-faceted hexagonal SLNR end planes of ZnO segments. The Li-doping effects which are occupied in interstitial site (Lii) or substitutional site (LiZn) in single crystalline ZnO SLNRs were carefully examined through the lattice spacing differences of lattice fringes in high-resolution transmission electron microscopy. An extensive analysis of the luminescence features was carried out in order to identify conduction type conversion from n-type to p-type in the Li-doped ZnO SLNRs. The appearance of acceptor-bound exciton emission, extremely enhancement of near-band-edge emission and the longer carrier life-time indicate that the Li dopants act as desirable shallow acceptor in the ZnO SLNRs. In addition, the SLNR-based p–n homojunctions exhibited distinct electrical features for their potential use as light emitting diodes and UV photovoltaics, thereby spurring progress in the development of practical optoelectronics. Figure 1

Interface modification of MoS2/SiO2 leading to conversion of conduction type of MoS2

Few-layer MoS2 prepared by the chemical vapor deposition method is deposited on SiO2 samples with/without sulfide treatment in order to experimentally study the mechanism of conduction-type conversion in MoS2. The MoS2 thin film deposited on a SiO2 substrate with sulfide treatment shows n-type behavior, whereas the MoS2 thin film deposited on a SiO2 substrate without sulfide treatment exhibits p-type behavior. Experimental identification confirms that n-type conversion is due to a combined effect of the broken SiO bonds and the formation of SiS bonds at the SiO2 surface that results in the removal of oxygen dangling bonds and a change in the MoS2SiO2 interaction.

N-type conduction in SnS by anion substitution with Cl

Relatively nontoxic, earth-abundant Cl was incorporated into n-type SnS as a dopant. The existence of impurity phases was carefully identified in Sn(S1−x−yClx)-dense ceramics. The highest electron mobility (8.3 cm2 V−1 s−1) in n-type conduction was achieved in samples with x ≥ 0.005. Cl concentration is critical for conduction-type conversion, whereas carrier density and electron mobility are determined by sulfur-site deficiency. Carrier transport is explained by grain boundary potential barrier scattering in undoped p-type samples and by ionized impurity scattering in Cl-doped n-type samples.

Electrical Characterization and Defect-Related Luminescence in Oxygen Implanted Silicon

Defect structure, electrical properties and defect-related luminescence (DRL) of light emitting diodes (LED) with the active defect-rich region produced by oxygen implantation and a subsequent multistep annealing of silicon wafers were investigated. It was found that defect-rich regions possess an embedded positive charge in both n-and p-type of the samples whose origin was ascribed to oxygen precipitates (OP). The presence of that charge in the implanted region of p-based LED gave rise to the apparent conductivity type conversion and to a significant increase of free electron concentration in n-based LEDs. A significant difference in the shape and in the excitation dependence of luminescence spectra as well as in the properties of DLTS signals was found between p-and n-type samples. From an analysis of the obtained data the DRL band centered at 0.79 eV was ascribed to small OPs segregated at dislocations whose filling with the holes hinders optical transitions via dislocation-related states at 0.805 eV and the broad DRL band at energies higher than 0.81 eV was ascribed to large OPs.