共查询到20条相似文献,搜索用时 15 毫秒
1.
J. N. Dai Z. H. Wu C. H. Yu Q. Zhang Y. Q. Sun Y. K. Xiong X. Y. Han L. Z. Tong Q. H. He F. A. Ponce C. Q. Chen 《Journal of Electronic Materials》2009,38(9):1938-1943
In this work, we have comparatively investigated the effects of the GaN, AlGaN, and AlN low-temperature buffer layers (BL)
on the crystal quality of a-plane GaN thin films grown on r-plane sapphire substrates. Scanning electron microscopy images of the a-plane GaN epilayers show that using an AlGaN BL can significantly reduce the density of surface pits. The full-width at half-maximum
values of the x-ray rocking curve (XRC) are 0.19°, 0.36°, and 0.48° for the films grown using Al0.15Ga0.85N, GaN, and AlN BLs, respectively, indicating that an AlGaN BL can effectively reduce the mosaicity of the films. Room-temperature
photoluminescence shows that the AlGaN BL results in lower impurity incorporation in the subsequent a-plane GaN films, as compared with the case of GaN and AlN BLs. The higher crystal quality of a-plane GaN films produced by the Al0.15Ga0.85N BL could be due to improvement of BL quality by reducing the lattice mismatch between the BL and r-sapphire substrates, while still keeping the lattice mismatch between the BL and epitaxial a-plane GaN films relatively small. 相似文献
2.
J. N. Dai X. Y. Han Z. H. Wu Y. Y. Fang H. Xiong Y. Tian C. H. Yu Q. H. He C. Q. Chen 《Journal of Electronic Materials》2011,40(4):446-452
In this work, a-plane GaN/r-sapphire templates have been used to grow nonpolar a-plane ZnO films by pulsed laser deposition. The ZnO film growth temperature was varied in the range of 400°C to 600°C, and
the effect of growth temperature on the properties of the ZnO thin films was investigated using x-ray diffraction, atomic
force microscopy, photoluminescence (PL) spectroscopy, and Raman measurements. The results show that the crystal quality,
surface morphology, strain states, and optical properties of a-plane ZnO films are strongly correlated with the deposition temperature. It is found that the crystallinity of the ZnO films
gets better and the surface roughness decreases with increasing growth temperature. At a growth temperature of 600°C, the
a-ZnO films display the best crystal quality with x-ray (11[`2]0) (11\bar{2}0) omega scan full-width at half-maximum values of 0.28° and 0.41° on axis (11[`2]0) (11\bar{2}0) at azimuth 0° and 90°, respectively. Furthermore, the PL spectrum measured at 83 K is dominated by neutral donor-bound excitons
and free-electron-to-bound (e-A
0) emission, and relatively intense LO-phonon replicas of (e-A
0) have also been observed in the a-plane ZnO. The dominance of the free exciton and the appearance of its replicas strongly indicate the high quality of the
film. 相似文献
3.
S. Liang C. R. Gorla N. Emanetoglu Y. Liu W. E. Mayo Y. Lu 《Journal of Electronic Materials》1998,27(11):L72-L76
There has been increased interest in high quality ZnO films for use in a diverse range of applications such as in high frequency surface acoustic wave filters, buffer layers for GaN growth, transparent and conductive electrodes, and solid state lasers. In the present paper, ZnO films were epitaxially grown on R-plane sapphire substrates by metalorganic chemical vapor deposition at temperatures in the range 350–450°C. X-ray diffraction and electron microscopy results indicate that the ZnO films are epitaxially grown on ( $01\bar 12$ ) Al2O3 surface with the ( $11\bar 20$ ) plane parallel to the surface. Cross-sectional high resolution-transmission electron microscopy imaging of the as-grown film shows that the interface is semi-coherent and atomically sharp, with misfit dislocations relieving the misfit strain between ZnO and sapphire. In order to check the thermal stability of the as-grown ZnO films, annealing in an O2+N2 ambience at 850°C for 30 min was performed. The annealed films showed improved crystallinity. At the same time, limited reaction between ZnO and sapphire occurred, resulting in the formation of a 15–20 nm thick spinel layer at the interface. 相似文献
4.
Single-crystalline nonpolar GaN epitaxial films have been successfully grown on r-plane sapphire (Al2O3) substrates by pulsed laser deposition (PLD) with an in-plane epitaxial relationship of GaN[1-100]//Al2O3[11-20]. The properties of the ~500 nm-thick nonpolar GaN epitaxial films grown at temperatures ranging from 450 to 880 °C are studied in detail. It is revealed that the surface morphology, the crystalline quality, and the interfacial property of as-grown ~500 nm-thick nonpolar GaN epitaxial films are firstly improved and then decreased with the growth temperature changing from 450 to 880 °C. It shows an optimized result at the growth temperature of 850 °C, and the ~500 nm-thick nonpolar GaN epitaxial films grown at 850 °C show very smooth surface with a root-mean-square surface roughness of 5.5 nm and the best crystalline quality with the full-width at half-maximum values of X-ray rocking curves for GaN(11-20) and GaN(10-11) of 0.8° and 0.9°, respectively. Additionally, there is a 1.7 nm-thick interfacial layer existing between GaN epitaxial films and r-plane sapphire substrates. This work offers an effective approach for achieving single-crystalline nonpolar GaN epitaxial films for the fabrication of nonpolar GaN-based devices. 相似文献
5.
Ultraviolet detectors based on epitaxial ZnO films grown by MOCVD 总被引:30,自引:0,他引:30
Y. Liu C. R. Gorla S. Liang N. Emanetoglu Y. Lu H. Shen M. Wraback 《Journal of Electronic Materials》2000,29(1):69-74
High-quality zinc oxide (ZnO) films were epitaxially grown on R-plane sapphire substrates by metalorganic chemical vapor deposition
at temperatures in the range of 350°C to 600°C. In-situ nitrogen compensation doping was performed using NH3. Microstructural and optical properties of the films, as well as the N-doping effects, were studied. The metal-semiconductor-metal
ultraviolet sensitive photodetectors were fabricated on N-doped epitaxial ZnO films. The detector showed fast photoresponse,
with a rise time of 1 μs and a fall time of 1.5 μs. Low-frequency photoresponsivity, on the order of 400 A/W at 5 V bias,
was obtained. 相似文献
6.
Y. I. Alivov X. Bo S. Akarca-Biyikli Q. Fan J. Xie N. Biyikli K. Zhu D. Johnstone H. Morkoç 《Journal of Electronic Materials》2006,35(4):520-524
We report on the electrical properties of ZnO films and devices grown on different substrates by radio-frequency magnetron sputtering. The films grown on c-plane sapphire were annealed in the range 800–1,000°C. The electron concentration increased with annealing temperature reaching 1.4×1019 cm?3 for 1,000°C. Mobility also increased, however, reaching its maximum value 64.4 cm2/V · sec for 950°C anneal. High-performance Schottky diodes were fabricated on ZnO films grown on n-type 6H-SiC by depositing Au/Ni(300/300 Å). After annealing at 900°C, the leakage current (at ?5 V reverse bias) decreased from 2.2 × 10?7 A to ~5.0 × 10?8 A after annealing at 900°C, the forward current increased by a factor of 2, and the ideality factor decreased from 1.5 to 1.03. The ZnO films were also grown on p-type 6H-SiC, and n-ZnO/p-SiC heterostructure diodes were fabricated. The p-n diode performance increased dramatically after annealing at 950°C. The leakage current decreased from 2.0×10?4 A to 3.0×10?7 A at ?10 V reverse bias, and the forward current increased slightly from 2.7 mA to 3.9 mA at 7 V forward bias; the ideality factor of the annealed diode was estimated as 2.2, while that for the as-grown sample was considerably higher. 相似文献
7.
我们在室温下测量采用反射差分光谱测量了r面蓝宝石衬底上生长的a面氧化锌的平面内光学各向异性。由于a面氧化锌为C2v对称性,我们观察到在平行c轴的方向和垂直于c轴的方向存在巨大的平面内光学各向异性。在带隙处观察到了非常尖锐的跃迁振荡信号,这个信号来源于偏振相关的能带移动。激子跃迁产生了尖锐的线形。谱线的拟合和微分光谱给出了偏振相关的带隙能量。垂直于c轴和平行于c轴方向上的各向异性应变产生了巨大的平面内光学各向异性。介电函数模型给出了拟合的结果,估计了带隙附近的偏振度。 相似文献
8.
Room-temperature ferromagnetic ordering in Mn-doped ZnO thin films grown by pulsed laser deposition 总被引:1,自引:0,他引:1
W. Y. Shim K. A. Jeon K. I. Lee S. Y. Lee M. H. Jung W. Y. Lee 《Journal of Electronic Materials》2006,35(4):635-640
The ferromagnetic ordering in Mn-doped ZnO thin films grown by pulsed laser deposition (PLD) as a function of oxygen pressure
and substrate temperature has been investigated. Room-temperature ferromagnetic behaviors in the Mn-doped ZnO films grown
at 700°C and 800°C under 10−1 torr in oxygen pressure were found, whereas ferromagnetic ordering in the films grown under 10−3 torr disappeared at 300 K. The large positive magnetoresistance (MR), ∼10%, was observed at 5 K at low fields and small negative
MR was observed at high fields, irrespective of oxygen pressure. In particular, anomalous Hall effect (AHE) in the Mn-doped
ZnO film grown at 700°C under 10−1 Torr has been observed up to 210 K. In this work, the observed AHE is believed to be further direct evidence demonstrating
that the Mn-doped ZnO thin films are ferromagnetic. 相似文献
9.
Tom Nelson Oder Andrew Smith Mark Freeman Michael Mcmaster Bo Cai Mim Lal Nakarmi 《Journal of Electronic Materials》2014,43(5):1370-1378
The properties of ZnO thin films codoped with lithium and phosphorus have been characterized. The films were deposited from high-purity ZnO and Li3PO4 solid targets onto c-plane sapphire substrates by radiofrequency (RF) magnetron sputtering. A substrate temperature of 900°C was determined as optimum for depositing undoped ZnO films with background electron concentration of 9.9 × 1015 cm?3 as the buffer layer on the sapphire substrate. Postdeposition annealing was carried out using rapid thermal processing in O2 at temperatures ranging from 500°C to 1000°C for 3 min. Analyses performed using low-temperature photoluminescence spectroscopy measurements revealed luminescence peaks at 3.356 eV, 3.307 eV, 3.248 eV, and 3.203 eV at 12 K for the codoped samples. X-ray diffraction 2θ-scans showed a single peak at about 34.4° with full-width at half-maximum of about 0.09°. Hall-effect measurements revealed initial p-type conductivities, but these were unstable and toggled between p-type and n-type over time with Hall concentrations that varied between 2.05 × 1013 cm?3 and 2.89 × 1015 cm?3. The fluctuation in the carrier type could be due to lateral inhomogeneity in the hole concentration caused by stacking faults in the films. An additional cause could be the small Hall voltages in the measurements, which could be significantly impacted by even small spikes in signal noise inherent in the measurements. 相似文献
10.
Taizo Nakasu Masakazu Kobayashi Hiroyoshi Togo Toshiaki Asahi 《Journal of Electronic Materials》2014,43(4):921-925
ZnTe epilayers have been grown on 2°-tilted m-plane $\left( {10\overline{1} 0} \right)$ sapphire substrates by molecular beam epitaxy. Pole figure imaging was used to study the domain distribution within the layer, and the pole figures of 111, 220, 004, and 422 ZnTe and $30\overline{3} 0$ sapphire were measured. Computer simulation was used to analyze the symmetry of the diffraction patterns seen in the pole figure images. Stereographic projections were also compared with the pole figures of 422 and 211 ZnTe, confirming that single-domain (211)-oriented ZnTe epilayers had been grown on the 2°-tilted m-plane sapphire substrates. Although differences in crystal structure and lattice mismatch were severe in these heterostructures, precise control of the substrate surface’s lattice arrangement would result in the formation of high-quality epitaxial layers. 相似文献
11.
Sun-Hong Park Chul-Hwan Choi Kyoung-Bo Kim Seon-Hyo Kim 《Journal of Electronic Materials》2003,32(11):1148-1154
High-quality ZnO thin films were prepared by metal-organic chemical vapor deposition (MOCVD) on a sapphire (a-Al2O3) substrate. The synthesis of ZnO films was performed over a substrate temperature of 400–700°C and at chamber pressures of
0.1–10 torr. The structural and optical properties of ZnO films were investigated in terms of deposition conditions, such
as substrate temperature, working pressure, and the ratio of Zn precursor (Diethylzinc (DEZn)) to oxygen. The ZnO films, preferentially
oriented to 34.42° diffraction because of the (002) plane, were obtained under processing conditions of 700°C and 3 torr.
This film shows a full-width at half-maximum (FWHM) of 0.4–0.6°. The results of photoluminescence (PL) spectroscopy also show
a strong near band-edge emission at 3.36 eV at 10 K as well as a very weak emission at deep levels around 2.5 eV at room temperature.
In addition, we are interested in the introduction of ZnO buffer-layer growth by the sputtering process to reduce lattice
mismatch stress. This paper addresses how to advance the crystalline and optical properties of film. The ZnO film grown with
the aid of a buffer layer shows a FWHM of 0.06–0.1° in the x-ray diffraction (XRD) pattern. This result indicates that crystalline
properties were highly improved by the ZnO buffer layers. The PL spectroscopy data of ZnO film also shows a strong near band-edge
emission and very weak deep-level emission similar to films synthesized without a buffer layer. Accordingly, synthesized ZnO
films with buffer layers indicate fairly good optical properties and low defect density as well as excellent crystallinity. 相似文献
12.
Gaurav Saraf Jian Zhong Olga Dulub Ulrike Diebold Theo Siegrist Yicheng Lu 《Journal of Electronic Materials》2007,36(4):446-451
The a-plane Mg
x
Zn1−x
O (0 ≤ x ≤ 0.3) films were grown on r-plane () sapphire substrates using metal-organic chemical vapor deposition (MOCVD). Growth was done at temperatures from 450°C to
500°C, with a typical growth rate of ∼500 nm/h. Field emission scanning electron microscopy (FESEM) images show that the films
are smooth and dense. X-ray diffraction (XRD) scans confirm good crystallinity of the films. The interface of Mg
x
Zn1−x
O films with r-sapphire was found to be semicoherent as characterized by high-resolution transmission electron microscopy (HRTEM). The Mg
x
Zn1−x
O surfaces were characterized using scanning tunneling microscopy (STM) in ultrahigh vacuum (UHV). Low-energy electron diffraction
(LEED) shows well-ordered and single-crystalline surfaces. The films have a characteristic wavelike surface morphology with
needle-shaped domains running predominantly along the crystallographic c-direction. Photoluminescence (PL) measurements show a strong near-band-edge emission without observable deep level emission,
indicating a low defect concentration. In-plane optical anisotropic transmission was observed by polarized transmission measurements. 相似文献
13.
J. Zhong S. Muthukumar G. Saraf H. Chen Y. Chen Y. Lu 《Journal of Electronic Materials》2004,33(6):654-657
The ZnO nanotips are grown on silicon and silicon-on-sapphire (SOS) substrates using the metal-organic chemical-vapor deposition
(MOCVD) technique. The ZnO nanotips are found to be single crystal and vertically aligned along the c-axis. In-situ Ga doping
is carried out during the MOCVD growth. The ZnO nanotips display strong near-band edge photoluminescence (PL) emission with
negligible deep-level emission. Free excitonic emission dominates the 77-K PL spectrum of the as-grown, undoped ZnO nanotips,
indicating good optical properties and a low defect concentration of the nanotips. The increase of PL intensity from Ga doping
is attributed to Ga-related impurity band emission. Photoluminescence quenching is also observed because of heavy Ga doping.
ZnO nanotips grown on Si can be patterned through photolithography and etching processes, providing the potential for integrating
ZnO nanotip arrays with Si devices. 相似文献
14.
Hanhong Chen Ziqing Duan Yicheng Lu Aurelien Du Pasquier 《Journal of Electronic Materials》2009,38(8):1612-1617
We present a dye-sensitized solar cell (DSSC) using a nanostructured ZnO photoelectrode and a gel electrolyte. The photoelectrode
consists of well-aligned ZnO nanotips on a Ga-doped ZnO (GZO) transparent conducting film. The GZO film (400 nm, sheet resistance
~25 Ω/sq, transmittance over 85% in the visible wavelength) and ZnO nanotips (3.2 μm length) are sequentially grown on a glass substrate using metalorganic chemical vapor deposition. The ZnO photoelectrode
is sensitized with dye N719 and impregnated with N-methyl pyrolidinone (NMP) gelled with poly(vinyl-difluoroethylene-hexafluoropropylene) copolymer (PVDF-HFP). The cell exhibits
an open-circuit voltage of 726 mV and a power conversion efficiency of 0.89% under one sun illumination. The aging testing
shows that the cell using a gel electrolyte has better stability than its liquid electrolyte counterpart. 相似文献
15.
H. Chen J. Zhong G. Saraf Y. Lu D. H. Hill S. T. Hsu Y. Ono 《Journal of Electronic Materials》2006,35(6):1241-1245
ZnO nanotips have been grown on Si (100) using metalorganic chemical vapor deposition (MOCVD). The growth temperature is optimized
for good crystallinity, morphology, and optical properties. ZnO nanotips exhibit a strong near band edge emission of ∼376
nm at room temperature with negligible green band emission. Pregrowth substrate treatment using diluted hydrofluoric acid
(HF) and minimized oxygen exposure before the initial growth significantly reduces the interfacial SiO2 thickness, while maintaining good morphology. An n-ZnO nanotips/p-Si diode is fabricated and its I–V characteristic is measured.
The threshold voltage of the diode is found to be below 2.0 V with small reverse leakage current. The ZnO/p-Si diodes provide
the possibility of integrating the ZnO nanotips with Si-based electronic devices. 相似文献
16.
M. Lorenz E. M. Kaidashev H. von Wenckstern V. Riede C. Bundesmann D. Spemann G. Benndorf H. Hochmuth A. Rahm H. -C. Semmelhack M. Grundmann 《Solid-state electronics》2003,47(12):2205
A consistent set of epitaxial, n-type conducting ZnO thin films, nominally undoped, doped with Ga or Al, or alloyed with Mg or Cd, was grown by pulsed laser deposition (PLD) on single-crystalline c-plane sapphire (0 0 0 1) substrates, and characterized by Hall measurement, and UV/VIS optical transmission spectroscopy.The optical band gap of undoped ZnO films at nearly 3.28 eV was shifted by alloying with Mg up to 4.5 eV and by alloying with Cd down to 3.18 eV, dependent on the alloy composition. In addition, highly doped ZnO:Al films show a blue-shifted optical absorption edge due to filling of electronic states in the conduction band.The Hall transport data of the PLD (Mg,Zn,Cd)O:(Ga,Al) thin films span a carrier concentration range of six orders of magnitude from 3 × 1014 to 3 × 1020 cm−3, which corresponds to a resistivity from 5 × 10−4 to 3 × 103 Ω cm. Structurally optimized, nominally undoped ZnO films grown with ZnO nucleation and top layer reached an electron mobility of 155 cm2/V s (300 K), which is among the largest values reported for heteroepitaxial ZnO thin films so far.Finally, we succeeded in combining the low resistivity of ZnO:Ga and the band gap shift of MgZnO in MgZnO:Ga thin films. This results demonstrate the unique tunability of the optical and electrical properties of the ZnO-based wide-band gap material for future electronic devices. 相似文献
17.
P. A. Grudowski A. L. Holmes C. J. Eiting R. D. Dupuis 《Journal of Electronic Materials》1997,26(3):257-261
We report the growth and characterization of unintentionally doped GaN on both exact and vicinal (0001) sapphire substrates.
The GaN heteroepitaxial layers are grown by metalorganic chemical vapor deposition on c-plane A12O3 substrates either on-axis or intentionally misoriented 2° toward the a-plane (1120) or 5 or 9° toward the m-plane (10 10). The samples are characterized by 300K photoluminescence, cathodoluminescence, and Hall-effect measurements
as well as by triple-axis x-ray diffractometry to determine the effect of the misorientation on the optical, electrical, and
structural properties of heteroepitaxial undoped GaN. Ten different sample sets are studied. The data reveal enhanced photo-luminescence
properties, increased electron mobility, a reduced n-type background carrier concentration, and a somewhat degraded surface morphology and crystalline quality for the misoriented
samples compared to the on-axis samples. 相似文献
18.
J. Zhong G. Saraf H. Chen Y. Lu Hock M. Ng T. Siegrist A. Parekh D. Lee E. A. Armour 《Journal of Electronic Materials》2007,36(6):654-658
ZnO nanotips are grown on epitaxial GaN/c-sapphire templates by metalorganic chemical vapor deposition. X-ray diffraction
(XRD) studies indicate that the epitaxial relationship between ZnO nanotips and the GaN layer is (0002)ZnO||(0002)GaN and
(101̄0)ZnO||(101̄0)GaN. Temperature-dependent photoluminescence (PL) spectra have been measured. Sharp free exciton and donor-bound
exciton peaks are observed at 4.4 K with photon energies of 3.380 eV, 3.369 eV, and 3.364 eV, confirming high optical quality
of ZnO nanotips. Free exciton emission dominates at temperatures above 50 K. The thermal dissociation of these bound excitons
forms free excitons and neutral donors. The thermal activation energies of the bound excitons at 3.369 eV and 3.364 eV are
11 meV and 16 meV, respectively. Temperature-dependent free A exciton peak emission is fitted to the Varshni’s equation to
study the variation of energy bandgap versus temperature. 相似文献
19.
J. Zhu N. W. Emanetoglu Y. Chen B. V. Yakshinskiy Y. Lu 《Journal of Electronic Materials》2004,33(6):556-559
This paper describes the optimized process of wet-chemical etching of a ZnO film grown on an r-plane sapphire. Different etchants
and solution ratios have been used to achieve controllable etching rate and steep etching profile. With selected etching solutions,
the etching profiles of epitaxially grown ZnO films (>1.3 μm) are improved. Using Al instead of photoresist as the mask generates
a steeper etching slope. Maximal 1:1 vertical/horizontal ratio (45°) has been achieved. X-ray photoelectron spectroscopy (XPS)
and sheet resistance measurements show that this wet-chemical etching process has negligible influence on the modification
of the physical and chemical properties of the etched surface. 相似文献
20.
Tri-Buffer Process: A New Approach to Obtain High-Quality ZnO Epitaxial Films on Sapphire Substrates
Z. X. Mei X. L. Du Y. Wang M. J. Ying Z. Q. Zeng H. T. Yuan J. F. Jia Q. K. Xue Z. Zhang 《Journal of Electronic Materials》2007,36(4):452-456
A tri-buffer method was applied to achieve layer-by-layer growth of high-quality ZnO films on sapphire (0001) substrates by
rf plasma-assisted molecular beam epitaxy (MBE). After sufficient nitridation of the substrate, MgO and ZnO buffer layers
were subsequently deposited on the resulting AlN layer. An atomically smooth ZnO surface with a roughness less than 1 nm in
a 10 μm × 10 μm scanned area was obtained with this method. The crystal quality was also improved, as characterized by reflection high-energy
electron diffraction (RHEED), x-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The
results indicate that the tri-buffer process could reduce the large lattice mismatch between ZnO and nitrided sapphire and
facilitate the two-dimensional (2-D) growth of the ZnO epilayer. A model is proposed to understand the observations. 相似文献