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1.
Combined Hall effect and low-temperature photoluminescence measurements have been used to perform a thorough evaluation of
the growth temperature dependence of Ge incorporation in GaAs during molecular beam epitaxy (MBE) over the entire substrate
temperature range (400°≦T
s
≦600[°C]) practicable forn-type layer growth. Using a constant As4 to Ga flux ratio of two, growth below 500°C yieldsn-GaAs: Ge films having electrical and optical properties rapidly deteriorating with decreasingT
s
. Growth at 500° ≦T
s
≦600[°C] produces high-qualityn-GaAs: Ge films (N
D
/N
A
≈4) with C as well as Ge residual acceptors competing on the available As sites. The amount of Ge atoms on As sites [GeAs] increases with substrate temperature, whereas simultaneously the amount of C atoms on As sites [CAs] decreases thus leading to the well-establishednonlinear behaviour of the (N
A
/N
D
vs. 1/T
s
plot. Counting the incorporated Ge impurities separately, however, yields alinear behaviour of the ([GeAs]/[GeGa]) vs. 1/T
s
plot which has exactly the same slope as the (P
As
2/P
Ga) vs. 1/T
s
plot derived from vapour pressure data of As2 and Ga over solid GaAs surfaces. The important result is, therefore, that the incorporation behaviour of Ge in GaAs during
molecular beam epitaxy is directly correlated with theevaporation behaviour of the growing GaAs surface. 相似文献
2.
Large-area ZnS nanowires were synthesized through a vapor phase deposition method. X-ray diffraction and electron microscopy results show that the products are composed of single crystalline ZnS nanowires with a cubic structure. The nanowires have sharp tips and are distributed uniformly on silicon substrates. The diameter of the bases is in the range of 320-530 nm and that of the tips is around 20-30 nm. The strong ultraviolet emission in the photoluminescence spectra also demonstrates that the ZnS nanowires are of high crystalline perfection. Field emission measurements reveal that the ZnS nanowires have a fairly low threshold field, which may be ascribed to their very sharp tips, rough surfaces and high crystal quality. The perfect field emission ability of the ZnS nanowires makes them a promising candidate for the fabrication of flexible cold cathodes. 相似文献
3.
W. Ryba-Romanowski S. Gołvab G. Dominiak-Dzik P. Solarz 《Applied Physics A: Materials Science & Processing》2002,74(4):581-586
Polycrystalline samples of europium-doped K5Li2GdF10 have been obtained by a slow cooling of melted compound and investigated using spectroscopy methods. Luminescence from the
5
D
2 level of Eu3+ is found to be weak. Intense visible emission upon excitation into the 5
D
2 or higher energy levels has been attributed to overlapping transitions from long-lived 5
D
1 and 5
D
0 levels. A strong increase of the 5
D
0 emission at the expense of the 5
D
1 emission occurs between 5 K and 25 K without significant change of the 5
D
1 lifetime. To account for this, it is supposed that both the radiative and the nonradiative transition rates are temperature-dependent.
Efficient energy transfer from the 6
G
J levels of Gd3+ to Eu3+ ions has been evidenced by excitation spectra in the VUV region and VUV-excited luminescence. It has been concluded that
the cross relaxation contributes to the energy-transfer process.
Received: 8 May 2001 / Accepted: 11 May 2001 / Published online: 25 July 2001 相似文献
4.
H. Künzel J. Knecht H. Jung K. Wünstel K. Ploog 《Applied Physics A: Materials Science & Processing》1982,28(3):167-173
Hall effect, DLTS and low-temperature photoluminescence measurements were used to study the effect of dimeric (As2) vs tetrameric (As4) vapour species on the electrical and optical properties of nominally undoped and of Ge-doped GaAs layers grown by molecular beam epitaxy (MBE). The arsenic molecular beam was generated from separate As2 and As4 sources, respectively, and from a single source providing an adjustable As2/As4 flux ratio. The occurence of the previously described defect related bound exciton lines in the luminescence spectra at 1.504–1.511 eV was found to be directly correlated with the presence of three deep states (M1, M3, M4) which are characteristic of MBE grown GaAs. The intensity of the extra luminescence lines and simultaneously the concentration of the deep electron traps can be reduced substantially simply by decreasing the As4/As2 flux ratio. The incorporation of defect related centers as well as of amphoteric dopants like Ge strongly depends on the surface chemistry involved. Therefore, a considerably lower autocompensation ratio in Ge-dopedn-GaAs is obtained with As2 molecular beam species which provide a higher steady-state arsenic surface population. 相似文献
5.
M.F. Plass C. Popov B. Ivanov S. Mändl M. Jelinek L.M. Zambov W. Kulisch 《Applied Physics A: Materials Science & Processing》2001,72(1):21-27
Amorphous nitrogen-rich carbon nitride (CNx) films have been prepared by inductively coupled plasma chemical vapour deposition (ICP-CVD) utilizing transport reactions
from a solid carbon source. The nitrogen atomic fraction N/(C+N) is about 1 or even higher as detected by various surface
and bulk sensitive methods. An investigation of the chemical bonding structure showed that the films are composed of >C=N
units with a small fraction of C≡N groups. Based on these findings, several structural units derived from cis- and trans-conjugated
carbon–nitrogen chains are proposed. The optical properties of the CNx films were studied by transmission spectroscopy and spectral ellipsometry; the optical Tauc gap was determined to 2.1±0.05 eV.
The photoluminescence characteristics were measured at three different excitation wavelengths (476, 488 and 515 nm) and revealed
two individual contributions. These data are interpreted in terms of the different structural units comprising the nitrogen-rich
CNx films.
Received: 14 July 2000 / Accepted:17 July 2000 / Published online: 22 November 2000 相似文献
6.
Dislocation-related photoluminescence in silicon 总被引:2,自引:0,他引:2
R. Sauer J. Weber J. Stolz E. R. Weber K. -H. Küsters H. Alexander 《Applied Physics A: Materials Science & Processing》1985,36(1):1-13
Photoluminescence is studied in silicon, deformed in a well-defined and reproducible way. Usual deformation conditions (high temperature, low stress) result in sharp spectra of the D1 through D4 lines as recently described in the literature. New lines D5 and D6 emerge for predeformation as above and subsequent low-temperature, high-stress deformation. Another new sharp line, D12, is observed when both the familiar and the novel lines appear simultaneously. Annealing for 1 h atT
A 300 °C causes all new lines to disappear and the D1–D4 spectra to reappear. Quantitative annealing and TEM micrographs suggest that D5 is related to straight dislocations and D6 to stacking faults, whereas D1–D4 are due to relaxed dislocations. Photoluminescence under uniaxial stress shows that D1/D2 originate in tetragonal defects with random orientation relative to 100 directions, whereas D6 stems from triclinic centers, preferentially oriented — as are the D3/D4 centers. We conclude that the D3/D4 and the D5 and D6 defects are closely related, whereas the independent D1/D2 centers might be deformation-produced point defects in the strain region of dislocations. 相似文献
7.
Vacuum Ultraviolet Excited Photoluminescence Properties of Novel Na3Y9O3(BO3)8:Tb^3+ Phosphor 总被引:1,自引:0,他引:1
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The novel vacuum ultraviolet (VUV) excited Na3 Y9O3 (BO3)8:Tb^3+ (NYOB:Tb^3+) green phosphor is prepared. Strong VUV photoluminescence and high quenching concentration of Tb^3+ (20 wt%) are observed in NYOB: Tb^3+ and the strong emission are correlated with the unique layer-type structure of NYOB. All the characteristic 4 f - 5d transitions of Tb^3+ and the host absorption band in VUV region are identified in the excitation spectrum. Based on the results, the energy levels scheme of Tb^3+ in NYOB:Tb^3+ is first established. This newly developed NYOB:Tb^3+ phosphor shows excellent optical properties when compared with the commercial Zn2SiO4:Mn^2+ and would be a potential VUV-excited green phosphor. 相似文献
8.
Sixfold symmetrical Mg-doped CdS nanowires have been fabricated through high temperature vapor-solid deposition process. The experimental study of the temperature-dependent photoluminescence properties of the Mg-doped CdS nanowires from 10 K to 300 K was reported. The Mg-doped CdS nanowires show intensive cyan-color light emission properties from 10 K to 200 K. The results indicate that there are two strong peaks situated at the green emission (at 528 nm) and red emission (at 655-695 nm), and two weak UV emission peaks at 378 nm and 417 nm, respectively. The ratio of green to red emission was decreased with temperature increased. When the temperature is above 200 K, the orange-color light was observed from the Mg-doped CdS nanowires. Therefore, the intensive emission properties of the Mg-doped CdS nanowires have a great potential for use as nanoscaled optoelectronic intensive light emitters under different temperature. 相似文献
9.
G.S. Chang J.H. Son K.H. Chae C.N. Whang E.Z. Kurmaev S.N. Shamin V.R. Galakhov A. Moewes D.L. Ederer 《Applied Physics A: Materials Science & Processing》2001,72(3):303-306
We have used ion-beam mixing to form Si nano-crystals in SiO2 and SiO2/Si multilayers, and applied photoluminescence and soft-X-ray emission spectroscopy to study the nanoparticles. Ion-beam mixing
followed by heat treatment at 1100 °C for 2 h forms the Si nanocrystals. The ion-beam-mixed sample shows higher PL intensity
than that of a Si-implanted SiO2 film. Photon and electron-excited Si L2,3 X-ray emission measurements were carried out to confirm the formation of Si nanocrystal in SiO2 matrix after ion-beam mixing and heat treatment. It is found that Si L2,3 X-ray emission spectra of ion-beam-mixed Si monolayers in heat-treated SiO2 films lead to noticeable changes in the spectroscopic fine structure.
Received: 20 November 1999 / Accepted: 17 April 2000 / Published online: 5 October 2000 相似文献
10.
A. Ruiz L. González A. Mazuelas F. Briones 《Applied Physics A: Materials Science & Processing》1989,49(5):543-545
InAs layers with thickness ranging from 0.1 to 2.5 m have been grown directly on highly mismatched (7.4%) (001) GaAs substrates by atomic layer molecular beam epitaxy (ALMBE). This growth method, based on the modulated deposition of one or both component species, provides InAs layers with excellent flat morphology, independently of the total thickness. A detailed study of the evolution of the electron diffraction (RHEED) pattern indicates that a complete decoupling between the InAs epitaxial layer and the GaAs substrate is reached in less that 10 monolayers. Evidence is obtained that layer-by-layer nucleation takes place from the beginning of the growth. 相似文献
11.
Strong Green Light Emission from Low-Temperature Grown a-SiNx:H Film after Different Oxidation Routes
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Room-temperature deposited amorphous silicon nitride (a-SiNx :H) films exhibit intense green light emission after post-treated by plasma oxidation, thermal oxidation and natural oxidation, respectively. All the photoluminescence (PL) spectra are peaked at around 500nm, independent of oxidation method and excitation wavelength. Compared with the PL results from oxidized a-Si:H and as-deposited a-SiNx:H samples, it is indicated that not only oxygen but also nitrogen is of an important role in enhancing light emission from the oxidized a-SiNx:H. Combining the PL results with the analyses of the bonding configurations as well as chemical compositions of the films, the strong green light emission is suggested to be from radiative recombination in luminescent centres related to N Si-O bonds. 相似文献
12.
The experimental study of the temperature-dependent photoluminescence properties of bicrystalline ZnS core/shell nanocables under 10 K to 300 K was reported. The results show that there are two distinct peaks situated at the UV (about 372.6 nm) and green (about 500 nm) regions, respectively, and one blue-shoulder band (about 465 nm) superimposed between them for all spectra. The UV peak shows an obvious redshift with increasing temperature. The analyses of Gaussian-fitted the blue-shoulder band and the green bands from 10 K to 300 K reveal that all spectra can be well fitted by three Gaussian peaks: blue peak (B, about 2.67 eV), two green peaks (G1, about 2.47 eV and G2, about 2.42 eV). With increasing temperature, the blue band shows blueshift. The green bands show anomalous transition: green band G1 shows blueshift-redshift transition and green band G2 shows redshift-blueshift. The origins of these bands and their temperature-dependent shifts are explained based on defect levels and strong carrier localization effect at the defect levels in addition to band-gap shrinkage. 相似文献
13.
Strong blue photoluminescence from aligned silica nanofibers 总被引:1,自引:0,他引:1
L. Dai X.L. Chen J.K. Jian W.J. Wang T. Zhou B.Q. Hu 《Applied Physics A: Materials Science & Processing》2003,76(4):625-627
Photoluminescence (PL) and infrared spectra of aligned silica nanofibers are investigated. Two striking strong blue luminescence
emissions have been found at room temperature. This suggests that the silica nanofibers could be a candidate material for
a blue-light emitter. The intensity of the PL emission decreases after annealing, which can be interpreted as the decrease
of the oxygen deficiency resulting in the reduction of radiative recombination centers. Infrared spectra provide further evidence
of this conclusion, where the enhancement of Si–O absorption is observed in annealed samples.
Received: 2 October 2002 / Accepted: 7 October 2002 / Published online: 8 January 2003
RID="*"
ID="*"Corresponding author. Fax: +86-10/8264-9531, E-mail: ldai@vip.sina.com 相似文献
14.
E. F. Schubert K. Ploog H. Dämbkes K. Heime 《Applied Physics A: Materials Science & Processing》1984,33(2):63-76
In selectively dopedn-AlxGa1–xAs/GaAs heterostructures with high-mobility two-dimensional electron gas (2 DEG) at the heterointerface a second conductive channel exists, if the AlxGa1–xAs layer is not totally depleted from free carries. The occurrence of parallel conductance has a deleterious effect on the performance of high-electron mobility transistors (HEMTs) fabricated from this material. Although in principle computable, parallel conductance depends on a large number of design parameters to be chosen for the heterostructure, which are additionally affected by the presence of deep electron traps inn-AlxGa1–xAs of composition 0.25n-AlxGa1–xAs/GaAs heterostructures is shown. 相似文献
15.
L.M. Moreira E.A. Cotta J.C. Gonzalez A.G. Oliveira F.M. Matinaga 《Solid State Communications》2007,143(3):166-170
Biexciton emission properties were studied in a single GaAs quantum well semiconductor planar microcavity by photoluminescence measurements at low temperatures. At high pump intensity a bipolariton emission appears close to the lower polariton mode. This new mode appears when we detune the cavity resonance out of the lower polariton branch, showing a laser-like behavior. Very small linewidths were measured, lying below 110 μeV and 150 μeV for polariton and bipolariton emission respectively. The input/output power (I/O) measurements show that the bipolariton emission has a weaker coupling efficiency compared to previous results for polariton emission. Varying the pump laser polarization, we were able to show the selection rules for the biexciton particle creation in the quantum well. Simultaneous photoluminescence and near-field measurements show that the polariton and bipolariton emission are spectrally and spatially separated. 相似文献
16.
In this Letter, 7F2 crystal field (CF) levels of surface Eu3+ in YVO4 nanocrystals are calculated employing a refined electrostatic point charge model, where surface states are simulated by point charges. Based on the theoretical 7F2 CF levels, emission spectra of YVO4: Eu3+ nanocrystals are assigned to Eu3+ under different local environments. and relaxation of selection rules by surface effect is discussed. 相似文献
17.
The incorporation of Sn into LPE GaAs was studied as a function of the atomic fractionx
Sn
l
of Sn in the liquid (1.6×10−4≤x
Sn
l
≤0.54), the growth temperatureT
K
and the cooling rate α. The diffusion coefficient of As in Ga for moderate Sn-doping was deduced from the growth velocities
to beD
As (760° C)=(3.3±1.0)×10−5 cm2/s. The epitaxial layers were analyzed after van der Pauw with special emphasis on the sources of experimental error. With
the aid of current mobility theories the concentrations of the ionized donors and acceptors were derived. From their dependence
onx
Sn
l
, on α and onT
K
combined with the Schottky-barrier model of Sn incorporation it can be concluded that the melt and the growing crystal surface
were in thermal equilibrium. The diffusion coefficient of Sn in GaAs is about 8×10−14 cm2/s at 760° C. The distribution coefficient for Sn increases from 4.4×10−5 to 12.3×10−5 in the temperature range from 690 to 800° C. The total Sn incorporationx
Sn
s
was measured using the atomic absorption spectroscopy for the first time down tox
Sn
s
=1017/cm3. From these data it can be concluded that up tox
Sn
l
=0.54 the dopant Sn is incorporated as donor and as acceptor only and that within the experimental scatter there is no indication
of incorporation as a neutral species. 相似文献
18.
We synthesize Y3Al5O12:Ce3+ (YAG:Ce3+) nanoparticles in the presence of citric acid by glycothermal method. Fourier transform infrared absorption spectroscopy measurement indicates that the intensity of the peak corresponding to carboxyl groups coordinating to the nanoparticles increases with increasing amount of citric acid. At the same time, the primary particle diameter decreases from 10.2 to 4.0 nm. In addition, the internal quantum efficiency of the photoluminescence (PL) due to the 4f-5d transition of Ce3+ increases from 22.0% to 40.1% with increasing amount of citric acid. Two kinds of PL decay lifetimes, 16-26 and 72-112 ns, are detected for YAG:Ce3+ nanoparticles, whereas the micron sized YAG:Ce3+ bulk shows the lifetime of 57 ns. We discuss these phenomena from the aspects of the coordination of citric acid and the incorporation of Ce3+ ions into the nanoparticles. 相似文献
19.
M. Bosund A. Aierken J. Tiilikainen T. Hakkarainen H. Lipsanen 《Applied Surface Science》2008,254(17):5385-5389
The suitability of titanium nitride (TiN) for GaAs surface passivation and protection is investigated. A 2-6-nm thick TiN passivation layer is deposited by atomic layer deposition (ALD) at 275 ° C on top of InGaAs/GaAs near surface quantum well (NSQW) structures to study the surface passivation. X-ray reflectivity measurements are used to determine the physical properties of the passivation layer. TiN passivation does not affect the surface morphology of the samples, but increases significantly the photoluminescence intensity and carrier lifetime of the NSQWs, and also provides long-term protection of the sample surface. This study shows that ALD TiN coating is a promising low-temperature method for ex situ GaAs surface passivation. 相似文献
20.
Structural and photoluminescence properties of thermally evaporated Cd1−xMnxS nano-crystalline films
D. Sreekantha Reddy D. Raja Reddy K.R. Gunasekhar B.K. Reddy 《Solid State Communications》2007,142(8):466-471
Thin films of Cd1−xMnxS (0≤x≤0.5) were formed on glass substrates by resistive vacuum thermal evaporation. All the films were deposited at 300 K and the films were annealed at 373, 473 and 573 K for 1 h in a vacuum of 10−6 mbar. Atomic force microscopy (AFM) studies showed that all the films investigated were in nano-crystalline form with a grain size in the range 36-82 nm. All the films exhibited a wurtzite structure of the host material. The lattice parameters varied linearly with composition following Vegard’s law in the entire composition range. Photoluminescence studies showed that two distinct emission bands were observed for each Cd1−xMnxS compound. One corresponds to internal transition and the other one is due to the transition of Mn2+ ions in interstitial sites or in small ‘Mn’ chalcogenic clusters. 相似文献