Byung-Teak Lee

Photoluminescence dependence of ZnO films grown on Si(100) by radio-frequency magnetron sputtering on the growth ambient

We report the effects of the growth ambient on photoluminescence (PL) emission properties of ZnO films grown on Si (100) by rf magnetron sputtering. Upon increasing the O2/Ar+O2 ratio in the growing ambient, the visible emission in the room-temperature PL spectra was drastically suppressed without sacrificing the band-edge emission intensity in the ultraviolet region. This tendency is estimated to be due to the reduction of the oxygen vacancies and zinc interstitials in the film induced by the improvement of the film stoichiometry with respect to high oxygen content, indicating that the visible emission in ZnO originates from oxygen vacancy or zinc interstitial related defects. The violet emission peaked at about 401 nm (3.09 eV) was observed in the low-temperature PL spectra of the ZnO films grown under oxygen-rich conditions. This emission band was assigned to the electron transition from the bottom of the conduction band to the Zn vacancy level, positioned approximately 3.06 eV below the conduction ban...

Preparation of As-doped p-type ZnO films using a Zn3As2∕ZnO target with pulsed laser deposition

We report the preparation of arsenic doped p-type ZnO films using a Zn3As2∕ZnO target by pulsed laser deposition. Zn3As2 was used as a p-type dopant source material for arsenic doping in ZnO. The existence of As in the As-doped ZnO films was confirmed by the x-ray photoelectron spectroscopy study. The p-type behavior of the As-doped ZnO films was determined by the Hall and photoluminescence measurements. Room temperature Hall measurements revealed that the As-doped ZnO films exhibited p-type conductivity after being annealed at 200°C in N2 ambient for 2min with the hole concentrations varied between 2.48×1017 and 1.18×1018cm−3. The resistivity and carrier mobility of the As-doped p-type ZnO films were in the range of 2.2–6.7Ωcm and 0.83–11.4cm2∕Vs, respectively. The low temperature photoluminescence measurements confirmed the peak associated with the neutral-acceptor bound exciton (A0X) emission in the As-doped p-type ZnO films.

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.

Pulsed-laser-deposited p-type ZnO films with phosphorus doping

We report the preparation of p-type ZnO thin films on Al2O3(0001) substrates with phosphorus doping by pulsed laser deposition using Zn3P2 as the dopant source material. The results of the Hall effect measurements taken at room temperature indicate that the 3‐mol% phosphorus-doped ZnO films thermally annealed at temperatures between 600 and 800°C under an O2 atmosphere exhibit p-type behavior with a hole concentration of 5.1×1014−1.5×1017cm−3, a hole mobility of 2.38−39.3cm2∕Vs, and a resistivity of 17−330Ωcm. The low-temperature (15K) photoluminescence results reveal that the peak related to the neutral-acceptor bound exciton (A0,X) emission at 3.358eV is only observed in the films showing p-type behavior. Our results not only demonstrate that there is a narrow temperature window for rapid thermal annealing in which phosphorus-doped p-type ZnO films can be obtained, but also suggest that the use of Zn3P2 can provide an effective approach to the preparation of p-type ZnO films.

Heteroepitaxial growth behavior of Mn-doped ZnO thin films on Al2O3 (0001) by pulsed laser deposition

Heteroepitaxial growth behavior of Mn-doped ZnO thin films (Zn1−xMnxO) on Al2O3 (0001) substrates by pulsed laser deposition was investigated particularly as a function of Mn content (0.00⩽x⩽0.35) using synchrotron x-ray scattering and atomic force microscopy. The undoped ZnO film was grown epitaxially with a 30° rotation of ZnO basal planes with respect to the Al2O3 substrate while having a small amount of grains with another epitaxial relationship, i.e., the hexagon-on-hexagon growth. A small amount of Mn doping (x=0.05) not only greatly improved the atomic alignment both in the in-plane and in the out-of-plane directions, but also led to a singly oriented film by totally suppressing the hexagon-on-hexagon growth. With further incorporation of Mn into ZnO beyond that content, the epitaxial nature again deteriorated. The superior epitaxial growth of the film with an optimum Mn content is attributed to the formation of much larger grains in it. In addition, our Mn-doped ZnO thin films showed a paramagneti...

Effects of growth conditions on the emission properties of ZnO films prepared on Si(100) by rf magnetron sputtering

ZnO films were prepared on Si(100) substrates using rf magnetron sputtering and the correlations between the growth conditions and the resultant film properties were discussed. The intensity of the visible emission related with intrinsic defects in ZnO film was dramatically suppressed by increasing the O2/Ar+O2 ratio in the growing ambient, which provides further evidence that the visible luminescence of ZnO originates from the oxygen vacancy or Zn interstitial related defects. It was also certain that the exciton related emission of ZnO is strongly dependent on the size of the micro-crystallites forming the film, showing the noticeable increase of the emission intensity with increasing grain size.

Growth and characterization of single crystalline Ga-doped ZnO films using rf magnetron sputtering

In this article it is shown that high quality single crystalline Ga-doped ZnO (GZO) films could be achieved on ac-plane sapphire using conventional rf magnetron sputtering. High-resolution x-ray diffractometry, transmission electron microscopy (TEM), and scanning electron microscopy investigations clearly confirmed that the GZO films with low Ga doping levels up to 1wt% were of high quality single crystal, which is featured by the (0002) rocking curve as narrow as 0.14°, symmetric six poles in pole figure, sharply defined spot pattern in the TEM diffraction diagram of the interfacial region, and the flat surface. It was also estimated from the Hall measurements and photoluminescence spectroscopy that these single crystalline GZO films possessed good optical and electrical characteristics including the narrow band-width and higher intensity of exciton-related emission peak, Hall mobility as large as 66 cm2 V−1 s−1, and the resistivity as low as 1.69 × 10− 3 Ω cm.

Growth and characterization of single crystal ZnO thin films using inductively coupled plasma metal organic chemical vapor deposition

Zinc oxide thin films were grown on sapphire substrates by metal organic chemical vapor deposition technique. Single crystal films with flat and smooth surfaces were reproducibly obtained, with application of sample bias and O2 inductively coupled plasma (ICP). At the growth condition of 650°C, 400W ICP power, −94V bias voltage and O∕Zn ratio of 75, full width at half maximum values of room temperature photoluminescence and high-resolution x-ray diffraction were measured to be 126meV and 269arcsec, respectively. It was proposed that application of sample bias provided reactant ions with kinetic energy, which promoted formation of single crystalline films.

Magnetron sputtering growth and characterization of high quality single crystal ZnO thin films on sapphire substrates

ZnO films were grown on sapphire substrates by rf magnetron sputtering and their structural and optical properties were characterized in detail. It was observed that high quality single crystal ZnO films are obtained when grown at high temperature (>600 °C) and low plasma power in oxygen-rich ambient. Films grown at 800 °C and 75 W in pure O2 showed sharp and intense photoluminescence (PL) and high resolution x-ray diffraction (XRD) peaks, with full-width-at-half-maximum values of 155 meV (room temperature PL), 23 meV (12 K PL) and 280 arcsec (XRD), which is comparable with previously reported values from ZnO films grown by more sophisticated techniques such as metal-organic chemical vapour deposition.

Microstructural interpretation of Ni ohmic contact on n-type 4H–SiC

Using cross-sectional transmission electron microscopy (TEM), microstructural changes in Ni contacts on n-type 4H–SiC as a function of annealing temperature were investigated. From these results, the correlation between the microstructural change and electrical properties was interpreted. After annealing at 800 °C, which yielded rectifying behavior, the silicide phases were formed, composed of Ni2Si and Ni31Si12. From the results shown in microbeam diffraction patterns, Ni31Si12 remains at the surface and Ni2Si is dominant in the contact, indicating that Ni2Si started to grow at the interface through the outdiffusion of Si atoms. When the sample was annealed at 950 °C, ohmic behavior was shown, and the layer structure was changed to a C-rich layer/Ni2Si/NiSi/n-type SiC. The NiSi phase was observed. These results imply that the composition of Si in nickel silicide at the interface with SiC increased with the increase of annealing temperature. The observation of the graphite phase at the surface indicates t...