Origin Of P-type Conductivity Research Articles

Origin of p-type conductivity in a WSe2 monolayer.

Transition-metal dichalcogenides have promising potentials for high-performance electronic and optoelectronic applications, which could be deeply influenced by defects, including native defects and dopants. Experiments to date have frequently reported p-type conductivity in the WSe2 monolayer, but the origin remains elusive. Here, using the first-principles calculations, we systematically investigate the point defects in the WSe2 monolayer and show that: (1) no intrinsic point defect is responsible for the p-type doping; (2) hydrogen interstitials (Hi) are possible sources for n-type conductivity; (3) oxygen substitution of Se (OSe) can greatly promote the formation of adjacent W vacancy (VW), and finally make VW relatively shallow acceptors by forming the defect complex nOSe + VW (n = 1 to 6). Our work reveals that nOSe + VW is the origin of the p-type conductivity in the unintentionally doped WSe2 monolayer, given that O is present throughout the synthesis conditions of WSe2.

Structural and electronic properties of Cu4O3 (paramelaconite): the role of native impurities

Abstract Hybrid density functional theory has been used to study the phase stability and formation of native point defects in Cu4O3. This intermediate copper oxide compound, also known as paramelaconite, was observed to be difficult to synthesize due to stabilization issues between mixed-valence Cu1+ and Cu2+ ions. The stability range of Cu4O3 was investigated and shown to be realized in an extremely narrow region of phase space, with Cu2O and CuO forming readily as competing impurity phases. The origin of p-type conductivity is confirmed to arise from specific intrinsic copper vacancies occurring on the 1+ site. Away from the outlined stability region, the dominant charge carriers become oxygen interstitials, impairing the conductivity by creating deep acceptor states in the electronic band gap region and driving the formation of alternative phases. This study further demonstrates the inadequacy of native defects as a source of n-type conductivity and complements existing experimental findings.

Direct n- to p-Type Channel Conversion in Monolayer/Few-Layer WS2 Field-Effect Transistors by Atomic Nitrogen Treatment.

We present a method for substitutional p-type doping in monolayer (1L) and few-layer (FL) WS2 using highly reactive nitrogen atoms. We demonstrate that the nitrogen-induced lattice distortion in atomically thin WS2 is negligible due to its low kinetic energy. The electrical characteristics of 1L/FL WS2 field-effect transistors (FETs) clearly show an n-channel to p-channel conversion with nitrogen incorporation. We investigate the defect formation energy and the origin of p-type conduction using first-principles calculations. We reveal that a defect state appears near the Fermi level, leading to a shallow acceptor level at 0.24 eV above the valence band maximum in nitrogen-doped 1L/FL WS2. This doping strategy enables a substitutional p-type doping in intrinsically n-type 1L/FL transition metal dichalcogenides (TMDCs) with tunable control of dopants, offering a method for realizing complementary metal-oxide-semiconductor FETs and optoelectronic devices on 1L/FL TMDCs by overcoming one of the major limits of TMDCs, that is, their n-type unipolar conduction.

Effect of ZnO twin grain boundary on p-type conductivity of VZn-NO-H complex:a GGA+U study

The origin of the p-type conductivity in N-doped ZnO has been a controversial issue for years, since isolated N substituted for O site (NO) was found to have high ionization energy. A recent experiment demonstrates that the p-type conductivity is attributed to the VZn-NO-H shallow acceptor complex. However, besides the complex, there are many other defects in ZnO, such as twin grain boundaries. They are commonly two-dimensional defects, and inevitably affect the p-type conductivity of the complex. By applying first principle calculations, we present the electronic structures and p-type conductivity of ZnO ∑7 (1230) twin grain boundaries containing VZn-NO-H complexes. Four types of ∑7 twin grain boundaries are investigated, and the VZn-NO-H complex is found to have a tendency to appearing in the stress raisers of the twin grain boundaries. The lowest formation energy under Zn-rich condition is only 0.52 eV for the complex in GB7a, a type of ∑7 twin grain boundary with anion-anion bonds, while the value is 3.25 eV for the complex in bulk ZnO. For the ionization energy, the complex in GB7a is more easily ionized, and has a value of 0.38 eV, compared with 0.67 eV in bulk ZnO. The result of density of states shows that the electron transition is dominated by the empty defect levels in forbidden band, which are occupied by O 2p and N 2p orbital. Further analysis indicates that the special structure of GB7a shortens the distances between NO and its neighbor O atoms, and the shortest N–O bond is only 2.38 Å, which also means a strong orbital hybridization between O and N. As a result, the energy level splitting is enhanced, and the empty energy level in the forbidden band is shifted down to valence band maximum. So, GB7a can favor the ionization in VZn-NO-H complex. Although GB7a is a special case of the twin grain boundaries, the result also gives us a new idea to understand the origin of p-type conductivity in N-doped ZnO.

Photoluminescence and photocatalytic properties of rhombohedral CuGaO2 nanoplates.

Rhombohedral phase CuGaO2 nanoplates with a diameter of about 10 μm were synthesized via low temperature hydrothermal method. Room temperature and low temperature photoluminescence of the obtained CuGaO2 nanoplates were characterized. CuGaO2 nanoplates exhibited blue emission at room temperature and free exciton emission were appeared at low temperature. The blue emission is originated from defects such as Cu vacancies, which is the possible origin of p-type conductivity. The appearance of free exciton emission can demonstrate the direct bandgap transition behavior of CuGaO2 nanoplates. The as-prepared p-type CuGaO2 nanoplates were further decorated by n-type ZnO nanoparticles via calcination method to fabricate p-n junction nanocomposites. The nanocomposites exhibited enhanced photocatalytic activity which can be ascribed to the effective separation of photogenerated carriers by the internal electrostatic field in the p-n junction region, and the enhanced light absorption properties resulted from sub-bandgap absorption effect of p-n junction. This work has offered a new insight into the design of p-n junction devices using p-type CuGaO2 nanoplates.

Investigation on non-polar m-plane ZnO and Na-doped p-type ZnO films grown by plasma-assisted molecular beam epitaxy

Non-polar ZnO and Na-doped ZnO films were epitaxially grown on m-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The films exhibit dominant ( $$ 10\overline{1} 0 $$ ) (m-plane) orientation as identified by the X-ray diffraction pattern. The quality of the obtained m-plane ZnO film is evidenced by X-ray diffraction rocking curves full width at half maximum of 1125 arcsec for the ( $$ 10\overline{1} 0 $$ ) reflection and 1427 arcsec for the ( $$ 10\overline{1} 1 $$ ) reflection, respectively. Hall-effect measurements show that the m-plane Na-doped ZnO film exhibits p-type conductivity with a hole concentration of 2.50 × 1017 cm−3, while the m-plane ZnO film exhibits compensatory conductivity. Na atoms substituting for Zn atoms are believed to be the origin of p-type conductivity. The Na-related acceptor level is deduced to be ~120 meV by temperature-dependent photoluminescence, indicating the superiority of m-plane ZnO film in p-type doping compared with the polar ZnO film.

Giant enhancement of the n-type conductivity in single phase p-type ZnO:N thin films by intentionally created defect clusters and pairs

Abstract The p-type conductivity with very high transparency in visible region of electromagnetic spectrum from nitrogen doped zinc oxide (ZnO:N) thin films is reported and the origin of p-type conductivity is attributed to the formation of complex zinc interstitial–nitrogen substituted oxygen (Zni–NO) centers. The films are irradiated using energetic ions for inducing the high density of defects/defect clusters in the lattice for increasing the conductivity of the films. A systematic change in nature of charge carriers from p- to n-type and about four orders of magnitude enhancement of n-type conductivity is observed with increase in the fluence of irradiation. The intentionally induced complex defects such as VO/Zni clusters and VZn–VO defects pairs are mainly ascribed to the donor defects. These induced defects also act as the compensatory defects for the p-type charge carriers at low fluences and give rise to the giant enhancement in the n-type conductivity of films at higher fluence of irradiation.

Low Temperature Methanol Sensing by p-Type Nano-titania: Correlation with Defects States and Schottky Barrier Model

In this paper, sol-gel derived undoped p-type nanotitania thin films particularly aimed to detect low ppm (5-100 ppm) methanol at low temperature (75-150°C) is reported. Anantase TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin film was deposited by sol-gel technique and p-type conductivity of the film was confirmed by Hall measurement. Nanocrystalline structure (12-15 nm) of the TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> film was confirmed by X-ray diffraction study and field emission scanning electron microscopy, respectively. Photoluminance spectroscopy and X-ray photoelectron spectroscopy were employed to characterize the defect structure. Methanol sensor study was carried for detecting the concentration range of 5 to 100 ppm in the temperature range of 75 to 150°C. Highly promising sensing performance was observed at an optimum operating temperature of only 100°C with 102% response magnitude (in 100 ppm methanol) and appreciably fast response and recovery time (~18 and ~21 s, respectively). The possible mechanism behind the origin of p-type conductivity has been correlated with the defect distribution model. Detailed sensing mechanism of the p-nano-titania has been explained using Schottky barrier model.

The origin of p-type conductivity in ZnM2O4 (M = Co, Rh, Ir) spinels

ZnM2O4 (M = Co, Rh, Ir) spinels are considered as a class of potential p-type transparent conducting oxides (TCOs). We report the formation energy of acceptor-like defects using first principles calculations with an advanced hybrid exchange-correlation functional (HSE06) within density functional theory (DFT). Due to the discrepancies between the theoretically obtained band gaps with this hybrid functional and the - scattered - experimental results, we also perform GW calculations to support the validity of the description of these spinels with the HSE06 functional. The considered defects are the cation vacancy and antisite defects, which are supposed to be the leading source of disorder in the spinel structures. We also discuss the band alignments in these spinels. The calculated formation energies indicate that the antisite defects ZnM (Zn replacing M, M = Co, Rh, Ir) and VZn act as shallow acceptors in ZnCo2O4, ZnRh2O4 and ZnIr2O4, which explains the experimentally observed p-type conductivity in those systems. Moreover, our systematic study indicates that the ZnIr antisite defect has the lowest formation energy in the group and it corroborates the highest p-type conductivity reported for ZnIr2O4 among the group of ZnM2O4 spinels. To gain further insight into factors affecting the p-type conductivity, we have also investigated the formation of localized small polarons by calculating the self-trapping energy of the holes.

Recent Developments of ZnO-Based P-Type Transparent Conductive Oxide Thin Films

Nowadays, high performance p-type transparent conductive oxide (TCO) thin films have gained tremendous intersts, and the fact is that if p-type TCOs with high electrical conductivity and optical transmittance can be fabricated, transparent p-n junctions can be obtained and invisible electronics be realized, and hence the use area of TCOs will be highly broadened. A lot of work have been done on non-stoichiometric and doped versions of p-type TCOs in the last few years to improve the optical and electrical properties by various deposition techniques. ZnO-based thin films were thought to be the most promising candidate for p-type TCOs based on the fact that ZnO has advantages over the others, so in this paper the development of ZnO-based p-type TCOs has been discussed. Firstly, the reasons why p-type ZnO-based TCOs are difficult to synthesize were discussed, and then the general ways now used to produce p-type ZnO-based TCOs were summerized, including intrinsic p-type ZnO, doping of groupelements, codoping of and elements, doping of group elements, the origin of p-type conductivity and the feasibility of each way, and the state-of-the-art optical and electrical properties were presented. Finally, the specific shortcomings in producing high quality p-type TCOs were discussed. Based on the comparision, it is believed that the doping of groupelements in ZnO may be the most pronising way in realizing p-type TCO.

The origin of p-type conduction in (P, N) codoped ZnO

P monodoped and (P, N) codoped ZnO are investigated by the first-principles calculations. It is found that the substitutional P defect at O site (PO) and interstitial P (Pi) contribute little to the p-type conductivity of ZnO samples under equilibrium condition. Zinc vacancies (VZn) and PZn-2VZn complex are demonstrated to be shallow acceptors with ionization energies around 100 meV, but they are easily compensated by PZn defect. Fortunately, PZn–4NO complexes may have lower formation energy than that of PZn under Zn-rich condition by proper choices of P and N sources. In addition, the neutral PZn–3NO passive defects may form an impurity band right above the valence-band maximum of ZnO as in earlier reported (Ga,N) or (Zr,N) doped ZnO. This significantly reduces the acceptor level of PZn–4NO complexes and helps improving the p-type conductivity in ZnO. It is suggested that a better (P, N) codoped p-type ZnO could be obtained under oxygen-poor condition.

P-type conduction in arsenic-doped ZnSe nanowires

Reliable p-type conduction was achieved in ZnSe nanowires (NWs) synthesized by introducing Zn3As2 as a dopant source. The crystal structure and orientation of NWs remained unchanged after doping. The electrical and transport properties of As-doped ZnSe NWs were investigated via the characteristics of NW-based field-effect transistors. The origin of p-type conduction in ZnSe NWs is attributed to the formation of substitutional AsSe and AsZn−2VZn complexes. Arsenic atoms were considered to incorporate into ZnSe lattices partly as As–H pairs; therefore postgrowth annealing could improve p-type conduction by dissociating As–H bonds and activating As acceptors.

P-Type Doping and Compensation in ZnO

Doping control is an important issue in wideband gap semiconductors such as nitrides and oxides that can be characterized by doping asymmetry, indicating that it is di cult to achieve both lowresistivity pand n-type semiconductors. Despite theoretical predictions that group-V acceptors have high activation energies, p-type ZnO doped with N, P, As and Sb has been experimentally realized with a maximum hole concentration reaching 1019 cm 3. Recently, p-type conduction was also reported in ZnO doped with Li impurities. Based on the results of rst-principles theoretical calculations, the electronic structure of various defects related to group-V and group-I dopants, the compensation mechanism of acceptors and the origin of p-type conduction in ZnO are discussed. Finally, control of p-type doping is examined with a focus on the activation of acceptors by co-doping with two di erent dopant sources and by hydrogenation followed by annealing.

The Origin of P-Type Conductivity in P-Doped ZnO

Based on first-principles theoretical calculations, we investigate the electronic structure of various defects in P-doped ZnO. We find that a PO impurity occupying an O site is a deep acceptor while a PZn atom at a Zn site is the dominant donor, causing a compensation of acceptors. Under O-rich growth conditions, Zn vacancies (VZn) are the main source of p-type conduction. Since VZn is mobile and strongly interacts with abundant PO and PZn defects, resulting complexes, such as PZn-2VZn and PO-VZn, which behave as acceptors, are likely to be formed under non-equilibrium growth conditions, and are responsible for the p-type conduction. We also investigate the eect of the strong Coulomb repulsion for the Zn d electrons on the electronic properties of various defects.

Fabrication of heterostructure p-β-Fe 0.95Mn 0.0 5Si 2/n-Si diodes by Fe + and Mn + co-implantation in Si(100) substrates

We report on the structural and electrical properties of iron silicides in the transformation process from ε-FeSi to β-FeSi 2 and show the electrical characteristics of heterostructure p-β-Fe 0.95Mn 0.05Si 2/n-Si diodes formed by high-dose Fe + and Mn + co-implantation in Si (100). A mixture of polycrystalline ε-FeSi and β-FeSi 2 with a thickness of 75 nm and the resistivity of ρ=4.9×10 −4 Ω·cm was in-situ formed during Fe +-implantation in Si (100) at 350°C. These samples were annealed at Ta=400–1100°C and characterized by Rutherford backscattering spectrometry, van der Pauw and X-ray diffraction. Single β-FeSi 2 layers with ρ=0.31 Ω·cm were formed after annealing at Ta =600°C. Although the samples with Ta<600°C exhibited p-type conductivity (hole concentrations of p=5.3–11×10 20 cm −3 and hole mobilities of μ h=8.7–32 cm 2/V/s), the samples with Ta≧600°C presented n-type conductivity ( n=4.2–14×10 16 cm −3 and μ e=220–520 cm 2/V/s). The origin of p-type conductivity may be due to contribution of Fe-rich β-FeSi 2, while that of the electron carrier could be related to the formation of stoichiometric β-FeSi 2, in which the predominant impurity phosphorous atoms remaining in the n-Si substrates could be electrically activated as donors in β-FeSi 2 by high-temperature annealing. The I–V and C–V characteristics of the p-β-Fe 0.95Mn 0.05Si 2/n-Si(100) diodes indicated that the impurity distribution of the pn junction is linearly graded, which leads to a high ideality factor of η=4.4.

On the origin of p-type conductivity in amorphous chalcogenides

An explanation for p-type conductivity in amorphous chalcogenides is given based on the role played by lone-pair electrons and charged defects. Valency alternation results in thermal excitation of free holes while free electrons are not created. Neutral dangling bonds are also a source of free holes. Existence of three-fold coordinated sites also explains the anomaly of the Hall effect in amorphous chalcogenides.