Ga Co-doping Research Articles

Codoping of aluminum and gallium with nitrogen in ZnO: A comparative first-principles investigation

We perform first-principles density-functional theory calculations to investigate the atomic structures and electronic properties of dopant complexes involving Al, Ga, and N in wurtzite ZnO. We find that both Al and Ga substituted on Zn sites act as single donors and exhibit a strong attractive interaction with a nitrogen acceptor located at the nearest-neighbor oxygen site in the same (0001) plane, forming passive (Al-N) and (Ga-N) complexes. These structures induce fully occupied defect states above the valence-band maximum of bulk ZnO. On introducing a higher concentration of nitrogen, (Al-2N) and (Ga-2N) complexes form. The additional N atom in these complexes prefers to occupy another nearest-neighbor site of the Al or the Ga atom, compared to being further away from it, and acts as an acceptor with ionization energies of 0.17 and 0.14 eV, respectively. These values are lower than the ionization energy of the single N acceptor, which is 0.33 eV. This indicates that (Al,N) and (Ga,N) codoping could increase the percentage of N dopants that are activated by ionization. The interaction between two (Al-N) complexes and the interaction between the (Al-2N) complex and a N atom (on a neighboring oxygen site) are very weak, indicating that the N concentration cannot be significantly increased by Al and N codoping or cluster doping. In contrast, two (Ga-N) complexes prefer to bind together in the same (0001) plane, implying that the passive complexes which create the impurity band could reach high concentration. The formation energy for (Ga-2N) is lower than (Al-2N) in the neutral and the negative charge states under most experimental conditions. Furthermore, the (Ga-2N) complex binds with additional N atoms located at nearest-neighbor O sites and therefore has a tendency to form clusters of (Ga-3N) and (Ga-4N). Under Zn-rich conditions and for an NO source of nitrogen, the cluster (Ga-3N) has a lower formation energy and lower transition levels compared to the (Ga-2N) complex; the (Ga-4N) complex has the lowest formation energy and the lowest $(0/1\ensuremath{-})$ transition energy among the (Ga,N) complexes. Our findings suggest that codoping of (Ga,N) could efficiently enhance the N dopant solubility with the NO source (rather than an ${\text{N}}_{2}$ source for nitrogen) and is likely to yield better $p$-type conductivity than (Al,N) codoping.

Luminescence Enhancement by Ga3+ Codoping of BaTiO3:Pr3+ Phosphors

The effects of dopant Pr and codopant Ga on the luminescence of BaTiO3 phosphors have been investigated. The maximum luminescence intensity of red emission was observed at a Pr concentration of 0.011 mol %, which is a much lower concentration than those in previous reports on the luminescence characteristics of phosphors. Ga codoping into BaTiO3:Pr3+ phosphors results in a marked increase in luminescence. This result has been interpreted from the viewpoint of symmetry, which makes the occurrence of band-to-band transition probable.

V and Ga Co-doping effect on optical absorption properties of TiO2 thin films

In this work, V and Ga co-doped TiO2 thin films were obtained by pulsed laser deposition (PLD) using sintered ceramic targets, followed by short term annealing at 1000°C. The structures of the thin films were characterized by X-ray diffraction (XRD) and the optical absorption properties of the films were investigated using UV-VIS spectrophotometer. A narrow energy band gap of about 1.5 eV was obtained in a typical co-doped film with 1 at.% V and 0.5 at.% Ga as dopants. The analysis on the chemical states of Ti and Ga elements by X-ray photoelectron spectroscopy (XPS) revealed that the Ga doping plays an important role in the band gap narrowing.

High minority carrier lifetime in Ga-doped Czochralski-grown silicon by Ge codoping

Higher minority carrier lifetimes (76 μs) were measured in Ga and Ge codoped Czochralski-silicon (CZ-Si) crystal compared to Ga-doped CZ-Si (28 μs). The minority carrier lifetime increase was associated with a decrease in etch pit density related to grown-in microdefects (GMD) in as-grown CZ-Si with increasing Ge concentration. Furthermore, oxygen (O) precipitation was enhanced in CZ-Si by increased Ge concentration, but this had a lesser limiting influence on minority carrier lifetime. The mechanism by which Ga and Ge codoping affects GMD suppression and enhances O precipitation in CZ-Si is discussed on the basis of the behavior of Ge-vacancy-O related complexes.

Carrier concentration tuning of bandgap-reduced p-type ZnO films by codoping of Cu and Ga for improving photoelectrochemical response

In this study, the synthesis of p-type ZnO films with similar bandgaps but varying carrier concentrations through codoping of Cu and Ga is reported. The ZnO:(Cu,Ga) films are synthesized by rf magnetron sputtering in O2 gas ambient at room temperature, followed by postdeposition annealing at 500°C in air for 2h. The bandgap reduction and p-type conductivity are caused by the incorporation of Cu. The tuning of carrier concentration is realized by varying the Ga concentration. The carrier concentration tuning does not significantly change the bandgap and crystallinity. However, it can optimize the carrier concentration to significantly enhance the photoelectrochemical response for bandgap-reduced p-type ZnO thin films.

Co-doping of aluminium and gallium with nitrogen in ZnO films deposited by RFmagnetron sputtering

N, (N + Ga) and(N + Al) doped ZnOfilms were deposited on c-plane sapphire substrates by RF magnetron sputtering at room temperature. Thesamples were characterized by their structural, surface morphological, compositionaland optical properties. The x-ray diffraction studies confirmed the co-doping of(N + Ga)and (N + Al) besides showing improvement in the crystallinity when compared with thesingle N doping. The surface of the films becomes rougher after co-doping. Thex-ray photoelectron spectroscopy and Rutherford back-scattering analysisindicate that the co-doping changes the chemical states and varies the amountof nitrogen (N) in ZnO. The amount of ‘N’ has been greatly increased for(N + Ga) co-doping, indicating that it is the best co-doping pair for p-type ZnO.Additionally, co-doping has increased the average visible transmittance (40–650 nm)and the optical band gap is shifted towards shorter wavelength. In the case of(N + Al) co-doping, the band gap becomes wider than that of undoped ZnO.

Preparation of p-type ZnO films with (N,Ga) co-doping by MOVPE

We investigate the p-type doping in ZnO prepared by metal–organic vapor phase epitaxy, using dimethylhydrazine (DMHy) as a nitrogen dopant source. Results obtained from X-ray photoelectron spectroscopy show that DMHy exhibits a narrow temperature window from 500 to 550 °C for efficient nitrogen doping. Additional co-doping with Ga significantly enhances the nitrogen incorporation and the conductivity type of the co-doped ZnO film is critically influenced by N/Ga flux ratio in growth. The fabricated p-type ZnO film shows a hole concentration of about 2.41 × 10 18 cm −3 and hole mobility of about 4.29 cm 2 V −1 s −1. The corresponding nitrogen acceptor level is calculated to be about 160 meV from the PL spectrum. I– V characterization of a p-ZnO:(N,Ga)/n-ZnO homojunction shows clear rectifying behavior with a turn-on voltage of about 3.7 V.

Growth of p-type ZnO thin films by (N, Ga) co-doping using DMHy dopant

We investigate p-type doping in ZnO prepared by metal-organic chemical vapour deposition with dimethylhydrazine (DMHy) as the nitrogen dopant source. Results obtained by x-ray photoelectron spectroscopy show that DMHy exhibits a narrow temperature window from 500 to 550 °C for efficient nitrogen incorporation and that nitrogen doping is critically influenced by growth conditions, e.g. the N/Ga flux ratio in growth. Within an appropriate N/Ga flux ratio range, p-type ZnO can be realized. The effect of the N/Ga flux ratio on the conductivity conversion of ZnO is reported. The extrinsic nitrogen acceptor level is calculated to be about 160 meV from low-temperature photoluminescence spectra.

Effect of GaN doping on ZnO films by pulsed laser deposition

The present study reveals the codoping of Ga and N into ZnO films on sapphire substrates by pulsed laser deposition (PLD) with GaN doped ZnO targets. The glow discharge mass spectroscopy (GDMS) spectra confirm the presence of Ga and N in the doped films. The XRD measurements show that for GaN concentration up to 0.8 mol%, the full width at half maximum (FWHM) is almost unchanged thereby maintaining the crystallinity of the films, while for 1 mol% the FWHM increases. The PL spectra only show the strong near band edge (NBE) emission, whereas the deep level emissions are almost undetectable, indicating that they have been considerably suppressed. Our Hall measurements indicate that all the GaN doped ZnO films are of n-type. However, as the GaN concentration is greater than 0.6 mol%, the film shows a decrease in the carrier concentration, suggesting that N acceptors are not sufficient to compensate the native donor defects.

Growth of epitaxial p-type ZnO thin films by codoping of Ga and N

Codoping of Ga and N was utilized to realize p-type conduction in ZnO films using rf magnetron sputtering. The films obtained at 550°C on sapphire showed resistivity and hole concentrations of 38Ωcm and 3.9×1017cm−3, respectively. ZnO films also showed a p-type behavior on p-Si with better electrical properties. ZnO homojunctions synthesized by in situ deposition of Ga–N codoped p-ZnO layer on Ga doped n-ZnO layer showed clear p-n diode characteristics. Low temperature photoluminescence spectra of codoped films also revealed a dominant peak at 3.12eV. The codoped films showed a dense columnar structure with a c-axis preferred orientation.

Codoping in ZnO using GaN by pulsed laser deposition

We report on the codoping of Ga and N into ZnO films by pulsed laser deposition with ZnO:GaN targets of different concentrations. The effect of GaN dopant on the structural, optical and electrical properties have been investigated. The X-ray diffraction (XRD) measurements show that for the GaN concentration up to 0.8 mol%, the full width at half maximum (FWHM) of (0 0 2) peak significantly reduces and thereby improves the crystallinity of the films while for 1 mol% the FWHM increases. For the GaN-doped films, the photoluminescence (PL) spectra show only a strong near band edge (NBE) emission and the deep level emissions are almost undetectable, indicating that GaN doping considerably suppresses the defect related emissions. The glow discharge mass spectroscopy (GDMS) spectra confirm the presence of Ga and N in the grown films. Our Hall measurements show that all the GaN-doped ZnO films are n-type, indicating that N acceptors are not sufficient to compensate the donors. The carrier concentrations have been increased till 0.8 mol% of GaN and decreased for 1 mol% GaN-doped film.

Role of Ga for Co-doping of Ga with N in ZnO Films

This study revealed that Ga and N co-doped ZnO films show an increase of solubility limits of N concentration through heavy doping with Ga; this is the “co-doping effect” proposed by Yamamoto and Yoshida [Jpn. J. Appl. Phys. Part 2 38 (1999) L166]. The N concentration increased linearly from 1018 to 1019 cm-3 when Ga concentration exceeded 8×1020 cm-3 but was almost constant at Ga concentrations below 2.3×1020 cm-3. This study also clarified that Ga concentrations of the order of 1020 cm-3 correspond to doping concentrations which change greatly from shallow donor sources releasing electrons to compensating-center trapping electrons. This fact suggests that the increased N concentration is attributable to the formation of the compensating-defects trapping carriers, such as GaZn–Ointerstitial and GaZn–VZn, in a metastable structure containing a high Ga concentration which exceeds the thermal equilibrium limit.

Thin ZnS:Cu,Ga and ZnO:Cu,Ga film phosphors

A new technique for electro- and cathodoluminescent screen fabrication with the application of a new method of doping ZnS:Cu and ZnO:Cu thin film phosphors is proposed. Thin films of ZnS:Cu were grown by electron-beam evaporation (EBE) from a ZnS:Cu target on substrates heated to 150–200°C, and the Cu concentration in the target was varied from 0.06 to 0.25 wt.%. BaTiO 3 and sapphire single crystal substrates were used. The film thickness varied from 0.6 to 9 μm. Parameters of ZnS:Cu films grown by EBE were modified by the use of non-vacuum annealing at 700–1000°C in S 2-rich or O 2-rich atmosphere both with and without Ga co-doping. The measurement of electroluminescent (EL) and cathodoluminescent (CL) parameters, as well as X-ray diffraction (XRD) techniques and atomic force microscopy (AFM) were used for this research. The EL ZnS:Cu,Ga blue color emission film with a luminance of 30 cd/m 2 and green (yellow) color emission film with a luminance of 800 cd/m 2 were obtained. Devices with such films have a threshold voltage of 10 V. The CL luminance was 200 cd/m 2 for ZnS:Cu,Ga and 1100 cd/m 2 for ZnO:Cu,Ga films at 300 K and 3700 cd/m 2 for ZnO:Cu,Ga films at 77 K. The films show a deeper green color than commercial phosphors. Clarification that gallium co-doping affects the luminance, since Ga influences on recrystallization process, has been carried out.

Co-doping Deposition of p-type ZnO Thin Films using KrF Excimer Laser Ablation

ABSTRACTWe report on the attempt to fabricate p-type ZnO thin films using various doping techniques based on the pulsed laser deposition (PLD). As an accepter, we have doped the N atom by using high purity nitric monoxide (NO) ambient gas. NO is dissociated into N and O at an energy of 6.5 eV which is lower than at N2 (9.76 eV). Moreover the dissociation reaction of NO is simpler than other nitrogenous gases such as N2O, NO2, and NH3. One of our doping techniques is co-doping of Ga and N atom by ablating ZnO:Ga target in NO gas, and another is the ablation of the metal Zn target in NO gas. Both of Ga and N co-doped ZnO films and N doped ZnO films have c-axis orientation as well as undoped ZnO films. The surfaces of these doped films are rough while the undoped ZnO thin film is very smooth and have hexagonally shaped grains. We found it possible to fabricate the p-type ZnO film by ablating the metal Zn target in NO gas.

Photoluminescence Charateristics of SrTiO3:Pr3+,Ga3+ Single Crystal

ABSTRACTSrTiO3 crystals containing varying concentrations of Pr and Ga were grown by a standard floating zone method and their photoluminescence characteristics were investigated. It was found that only a small fraction of Pr ions added are incorporated in the lattice. When the Ga ions are co-doped, the solubility of Pr ions is increased considerably. Comparing the ionic sizes of the host and dopants, it seems that the increase of solubility of Pr by Ga co-doping is due to charge compensation achieved by the additional Ga3+. The addition of Ga in Pr - activated SrTiO3 resulted also in a considerable enhancement of Pr3+ emission band at 615 nm. This result is attributed to the hole trapping effect of Ga3+ ions.