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PL spectrum at 10 K: solid line-sample 1, ZnO:As:N; open triangles-sample 2, polycrystalline p-ZnO doped only with N on ZnTe; dash line-sample 3, monocrystalline compensated ZnO:N layer on GaN, and open triangles-sample 4, p-ZnO doped only with As on GaAs substrate. A D 0 X(As) denotes exciton bound to deep acceptor complex containing As.
Source publication
ZnO doped with N and/or As layers was fabricated by thermal oxidation of ZnTe films grown by MBE on different substrates. Hall effect measurements demonstrated p-type conductivity with a hole concentration of ~5 × 1019 cm−3 for ZnO:As and ZnO:As:N on GaAs substrates and ~6 × 1017 cm−3 for ZnO:N on ZnTe substrates. The concentration of N and As atom...
Contexts in source publication
Context 1
... of PL from all types of samples is shown in figure 4. The photoluminescence peak located at 3.311 eV is observed in samples (1) and (2) doped only with N. It is worth noting that emission at this energy is not observed in the sample doped only with As (open circles in figure 4). ...
Context 2
... of PL from all types of samples is shown in figure 4. The photoluminescence peak located at 3.311 eV is observed in samples (1) and (2) doped only with N. It is worth noting that emission at this energy is not observed in the sample doped only with As (open circles in figure 4). On the other hand, in the ZnO:As sample we observe emission at 3.322 eV. ...
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Citations
... Unwanted intrinsic donor defects, low dopant solubility, and large dopant ionization energy are the main obstacles in making p-type ZnO [31][32][33][34]. Among others, group V elements are considered one of the most promising dopants for p-type ZnO and phosphorus (P) is one of them [35][36][37][38][39]. Previous studies suggested amphoteric nature of p-type dopants, where growth ambience and annealing have a very crucial effect [40,41]. ...
Zinc oxide (ZnO) offers a major disadvantage of asymmetry doping in terms of reliability, stability, and reproducibility of p-type doping, which is the main hindrance in realization of optoelectronic devices. The problem is even more complicated due to formation of various native defects in unintentionally doped n-type ZnO. The realization of p-type conductivity in doped ZnO requires an in-depth understanding of the formation of an effective shallow acceptor, as well as donor-acceptor compensation. Photophysical properties such as photoconductivity along with photoluminescence (PL) studies have unprecedentedly and effectively been utilized in this work to monitor the evolution of various in-gap defects. Phosphorus (P) doped ZnO thin films have been grown by RF magnetron sputtering under various Ar to O2 gas ratios to investigate the effect of O2 on the donor-acceptor compensation by comprehensive photoconductivity measurements supported by the PL studies. An initial elemental analyses indicate presence of abundant zinc vacancies (VZn) in O-rich ambience. The results predict that P sits in the zinc (Zn) site rather than the O site causing the formation of PZn–2VZn acceptor-like defects, which compensates the donor defects in P doped ZnO films. Photocurrent spectra uniquely reveal presence of more oxygen vacancies (VO) defects states in lower O2 flow, which gets compensated with an increase in the O2 flow. Successive photocurrent transients indicate probable presence of more VO in the films grown with lower O2 flow and more VZn in higher O2 flow. Overall the photosensitivity measurements clearly present that O-rich ambience expedites the formation of acceptor defects which are compensated, thereby lowering the dark current and enhancing the ultraviolet photosensitivity.
... We can summarize our characterization effort by stating that the oxidation of ZnTe NWs performed at temperature of 300 • C yields different results depending on whether the bare ZnTe or Zn-covered ZnTe NWs are processed. In the case of ZnTe NWs, our findings confirm earlier findings of Lu et al. [25] (T O = 260 • C) that for the oxidation performed substantially below 600 • C (i.e., below the optimum temperature for ZnTe → ZnO transformation [23,24]), instead of sharp ZnTe/ZnO interfaces-a ZnTe/Te/ZnO sequence is obtained. As argued in [25] the dominant mechanism at such low temperatures is the out-diffusion of Zn atoms towards the NWs' surface and formation of ZnO crystals by combining with atmospheric oxygen. ...
... We can summarize our characterization effort by stating that the oxidation of ZnTe NWs performed at temperature of 300 °C yields different results depending on whether the bare ZnTe or Zn-covered ZnTe NWs are processed. In the case of ZnTe NWs, our findings confirm earlier findings of Lu et al. [25] (TO = 260 °C) that for the oxidation performed substantially below 600 °C (i.e., below the optimum temperature for ZnTe → ZnO transformation [23,24]), instead of sharp ZnTe/ZnO interfaces-a ZnTe/Te/ZnO sequence is obtained. As argued in [25] the dominant mechanism at such low temperatures is the out-diffusion of Zn atoms towards the NWs' surface and formation of ZnO crystals by combining with atmospheric oxygen. ...
Results of comparative structural characterization of bare and Zn-covered ZnTe nanowires (NWs) before and after thermal oxidation at 300 °C are presented. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, and Raman scattering not only unambiguously confirm the conversion of the outer layer of the NWs into ZnO, but also demonstrate the influence of the oxidation process on the structure of the inner part of the NWs. Our study shows that the morphology of the resulting ZnO can be improved by the deposition of thin Zn shells on the bare ZnTe NWs prior to the oxidation. The oxidation of bare ZnTe NWs results in the formation of separated ZnO nanocrystals which decorate crystalline Te cores of the NWs. In the case of Zn-covered NWs, uniform ZnO shells are formed, however they are of a fine-crystalline structure or partially amorphous. Our study provides an important insight into the details of the oxidation processes of ZnTe nanostructures, which could be of importance for the preparation and performance of ZnTe based nano-devices operating under normal atmospheric conditions and at elevated temperatures.
... At the high nitrogen concentration in ZnO similar detection limit is achieved using the cesium primary beam and NCs + ions detection [75,[193][194][195][196][197]. These conditions are effective for thin film measurement with low primary beam energy and heavy primary beam ions assuring better depth resolution. ...
The paper addresses the role of ambient elements (H, C, N and O) in the wide-bandgap semiconductor compounds. Their prevalence in the atmosphere imposes limitations not only on the purity of the materials under processing but, also, on the detection and measurement of the content of these species. Specifically, a review of electrical and optical properties, based on the available literature, is presented for: hydrogen in GaN, ZnO and SiC, carbon in GaN and ZnO, nitrogen in ZnO and SiC and oxygen in GaN and SiC. Further, the refinements of the SIMS (Secondary Ions Mass Spectrometry) analytical technique, aiming to improve the sensitivity and detection limit of atmospheric elements, are described in detail. These include the choice of primary beam type and current, type of secondary single or cluster ions, geometry and vacuum conditions. Finally, the evaluated so-called RSF parameters (Relative Sensitivity Factors) are given for each atom-semiconductor pair, converting raw data to the absolute value of concentration.
... In the annealed ZnO:N sample the new peak at 3.355 eV arises, which can be interpreted as the A°X transition. A line at this energy was formerly observed in Na or in P-doped ZnO [28] as well as in ZnO:N and, in the latter case, related to a nitrogen acceptor [29,30]. The assignment of the 3.355 eV emission to the A°X transition is also supported by investigations of Tang et al. [24], who have observed that a monotonous increase of this line with annealing temperature is correlated with higher p-type conductivity. ...
In this paper we present luminescence results of nitrogen doped and undoped ZnO layers grown at 100 °C by atomic layer deposition and post grown annealed. A comprehensive analysis of the excitonic peaks as well as the controversial band at ~3.32 eV is presented. Based on temperature dependent luminescence analysis we identified PL peaks originating from donor and acceptor bound excitons D°X and A°X. It has been found that two acceptor-related PL peaks observed between 3.30 and 3.32 eV reveal different temperature behavior. The emission at 3.302 eV has been assigned to donor-acceptor pairs (DAP), whereas the emission at 3.318 eV to free electrons to acceptor transition. Activation of an acceptor as a result of high temperature annealing is reflected in PL spectra as an appreciable increase of the DAP emission.
The binding energies of existing donors and acceptors have been also calculated and the possible origin of the donors and acceptors in ZnO and ZnO:N layers grown at low temperature was proposed. Furthermore, the planar cathodoluminescence images discover that acceptor related emission comes from whole grains area.
... The PL line at this energy has been previously observed in ZnO:N films, related to nitrogen acceptor and interpreted as the exciton bound to neutral acceptor A 0 X transition. 2,28 Apart from the excitonic emission described above, the ZnO and ZnO:N films show photoluminescence in the region between 3.30 and 3.32 eV. This PL band has been variously assigned in the literature to many different acceptor-related transitions like acceptor-bound excitons, donor−acceptor pairs (DAPs) and free electron to neutral acceptor (FA). ...
Nitrogen doped and undoped ZnO films were grown by thermal Atomic Layer Deposition (ALD) under oxygen rich conditions. Low temperature photoluminescence spectra reveal a dominant donor-related emission at 3.36 eV and characteristic acceptor-related emissions at 3.302 and 3.318 eV. Annealing at 800oC in oxygen atmosphere leads to conversion of conductivity from n to p-type, which is reflected in photoluminescence spectra. Annealing does not increase any acceptor-related emission in the undoped sample, while in the ZnO:N it leads to a considerable enhancement of the photoluminescence at 3.302 eV. The high resolution cathodoluminescence cross-section images show different spatial distribution of the donor-related and the acceptor-related emissions, which complementarily contribute to the overall luminescence of the annealed ZnO:N material. Similar area of both emissions indicates that the acceptor luminescence comes neither from the grain boundaries nor from stacking faults. Moreover, in ZnO:N the acceptor-emission regions are located along the columns of growth, which shows a perspective to achieve a ZnO:N material with homogeneous acceptor conductivity at least at the micrometer scale.
... For as-grown sample S3, one dominant PL peak was seen with increasing annealing temperature. For low temperature annealed sample S3, the PL peaks were at 3.34 and 3.32 eV and corresponded to the free-exciton transition and donor-bound exciton transition, respectively [58,59]; furthermore, the peak intensities increased with increasing annealing temperature. Increasing oxygen content during growth results in suppression of defect levels and favorable stoichiometry. ...
High-quality radio frequency–sputtered ZnO were grown on Si substrates at 400 °C at various partial gas
pressures (Ar/Ar+O2). Subsequently, to remove as-grown defects, high temperature annealing from 700 to
900 °C on as-grown samples in constant oxygen flow for 10 s was performed. X-ray diffraction study confirmed
the formation of highly crystalline films with a dominant peak at (002). The sample grown in 50% Ar and 50%
O2 ambient exhibited the lowest linewidth (2θ=~0.2728°) and highest stoichiometry. Grain size of the as grown
samples decreased with increase in the partial pressure of oxygen till a certain ratio (1:1), and photoluminescence
(PL) improved with increase in annealing temperature. Low-temperature (18 K) PL measurements showed
a near-band-edge emission peak at 3.37 eV, and the highest peak intensity (more than six orders compared to
others with narrow linewidth of ~0.01272 eV) was exhibited by the sample annealed at 900 °C and was six
orders higher than that of the as-grown sample. All as-grown samples exhibited dominant visible-range peaks
due to emission from defect states.
... [2] However, the application of ZnO in optoelectronics is hindered by the lack of a stable p-doping because of the native defect: the O vacancy (V O ) and the Zn interstitial (i Zn ), [3] or hydrogen doping in ZnO. [4] Many methods have been carried out to fabricate p-type ZnO by doping of group-V (N, P, As, Sb) [5][6][7] and group-I [Li], [8] among which, N is predicted to be an outstanding dopant candidate, [9] but the real application is unfortunately limited by its low solubility in ZnO. On the other hand, it has been suggested by the calculation that Mg could improve the solubility of nitrogen in the ZnO. ...
Undoped ZnO and doped ZnO films were deposited on the MgO(111) substrates using oxygen plasma-assisted molecular beam expitaxy. The orientations of the grown ZnO thin film were investigated by in situ reflection high-energy electron diffraction and ex situ x-ray diffraction (XRD). The film roughness was measured by atomic force microscopy, which was correlated with the grain sizes determined by XRD. Synchrotron-based x-ray absorption spectroscopy was performed to study the doping effect on the electronic properties of the ZnO films, compared with density functional theory calculations. It is found that, nitrogen doping would hinder the growth of thin film, and generate the NO defect, while magnesium doping promotes the quality of nitrogen-doped ZnO films, inhibiting (N2)O production and increasing nitrogen content.
... Realization of p-ZnO with As doping has been demonstrated by several groups for layers obtained with different growth techniques, such as thermal oxidation of ZnTe deposited on GaAs [18], radio frequency sputtering [19,20], pulsed laser deposition [21], hybrid beam epitaxy [13], and ion implantation [22]. Although p-type conductivity of ZnO:As was obtained, the location of As dopant in the lattice of ZnO as well as the local atomic configuration around As is still under debate and needs clarification. ...
... Among them, nitrogen is considered as potentially the most promising p-type dopant [2][3][4] and there are many reports on p-type conductivity achieved in N-doped ZnO. [5][6][7] However, it is known that nitrogen acceptors can be compensated by Ovacancies as well as by the formation of N O -Zn O complexes. 8 Moreover, isolated N O forms a rather deep acceptor center in ZnO. 9 Theoretical calculations suggest also that it can be difficult to achieve high hole carrier densities because of the compensation of N-acceptors by N 2 molecules substituting O anions. ...
The high quality p-n structures studied consist of nitrogen doped ZnO:N films grown by plasma assisted molecular beam epitaxy on n-type GaN templates. The nitrogen concentration, determined by secondary ion mass spectroscopy, is about 1 × 1020 cm−3. Temperature dependent photoluminescence studies confirm the presence of acceptor centers with an energy level lying approximately 130 meV above the valence band. The maximum forward-to-reverse current ratio IF/IR in the obtained p-n diodes is about 107 at ±5 V, which is 2–5 orders of magnitude higher than previously reported for this type of heterojunctions. Electron-beam-induced current measurements confirm the presence of a p–n junction, located at the p-ZnO/n-
GaN interface. The calculated diffusion length and activation energy of minority carriers are presented. The heterostructures exhibit strong absorption in the UV range with a four orders of magnitude high bright-to-dark current ratio.
... doping was already presented [18], and p-ZnO : As samples were obtained by several techniques such as radio frequency sputtering [19] [20] [21], metal organic chemical vapour deposition (MOCVD) [22], thermal oxidation of ZnTe on GaAs [23], pulsed laser deposition PLD [24] and hybrid beam epitaxy [15]. Heterojunctions of p-ZnO : As/n-GaN, with ZnO : As layers obtained by MBE, has not been demonstrated yet. ...
We report on the characterization of wide-band-gap heterojunction diodes based on the p-ZnO/n-GaN material system. The layer structure consists of 11 µm GaN on sapphire substrates and As-doped ZnO film of thickness 0.4 µm obtained by plasma-assisted molecular beam epitaxy (PA-MBE). The quality of the heterojunction was examined by x-ray diffraction, atomic force microscopy and scanning electron microscopy. The arsenic concentration in ZnO, measured by secondary ion mass spectroscopy (SIMS), is 5 × 10 20 cm −3 . The maximum forward-to-reverse current ratio I F /I R is of about 10 5 in the applied voltage ±3 V, a very good result for this type of heterojunction. (Some figures may appear in colour only in the online journal)
