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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.
O. Tejayadi Y.L. Sun J. Klem R. Fischer M.V. Klein H. Morkoç 《Solid State Communications》1983,46(3):251-254
The effects of growth and pre-growth conditions on the background concentration of carbon in high quality undoped GaAs layers grown by molecular beam epitaxy have been studied. Characterization of the layers by low temperature photoluminescence indicates that a growth temperature of 580°C minimizes carbon contamination, and extended pre-growth outgassing of the substrate under an As4 over-pressure results in increased carbon concentrations. The carbon incorporation was found to be relatively insensitive to outgassing temperature above 615°C. Contrary to expectations, increasing the As/Ga flux ratio during growth resulted in larger carbon luminescence peaks. 相似文献
3.
P. Kratzer E. Penev M. Scheffler 《Applied Physics A: Materials Science & Processing》2002,75(1):79-88
We demonstrate how first-principles calculations using density-functional theory (DFT) can be applied to gain insight into
the molecular processes that rule the physics of materials processing. Specifically, we study the molecular beam epitaxy (MBE)
of arsenic compound semiconductors. For homoepitaxy of GaAs on GaAs (001), a growth model is presented that builds on results
of DFT calculations for molecular processes on the β2-reconstructed GaAs (001) surface, including adsorption, desorption,
surface diffusion, and nucleation. Kinetic Monte Carlo simulations on the basis of the calculated energetics enable us to
model MBE growth of GaAs from beams of Ga and As2 in atomistic detail. The simulations show that island nucleation is controlled by the reaction of As2 molecules with Ga adatoms on the surface. The analysis reveals that the scaling laws of standard nucleation theory for the
island density as a function of growth temperature are not applicable to GaAs epitaxy. We also discuss heteroepitaxy of InAs
on GaAs (001), and report first-principles DFT calculations for In diffusion on the strained GaAs substrate. In particular,
we address the effect of heteroepitaxial strain on the growth kinetics of coherently strained InAs islands. The strain field
around an island is found to cause a slowing down of material transport from the substrate towards the island, and thus helps
to achieve more homogeneous island sizes.
Received: 2 May 2001 / Accepted: 23 July 2001 / Published online: 3 April 2002 相似文献
4.
Nominally undoped AlxGa1–xAs grown by molecular beam epitaxy from As4 species at elevated substrate temperatures of 670°C exhibits well-resolved excitonic fine structure in the low-temperature photoluminescence spectra, if the effective As-to-(Al+Ga) flux ratio on the growth surface is kept within a rather narrow range of clearly As-stabilized conditions. In contrast to previous results on AlxGa1–xAs of composition 0.15not to shift in energy by changing the excitation intensity. This implies a simple freeelectron carbon-acceptor recombination mechanism for the line without any participation of a donor. In AlxGa1–xAs of composition close to the direct-to-indirect cross-over point, two distinct LO-phonons separated by 34 and 48 meV from the (D
0,C
0) peak position at x=0.43 were observed which were before only detectable by Raman scattering experiments. The intensity of the carbon-impurity related luminescence lines in bulk-type AlxGa1–xAs and GaAs layers was found to be strongly reduced, as compared to the excitonic recombination lines, if the respective active layer was covered by a very thin confinement layer of either GaAs on top of AlxGa1–xAs or vice versa grown in the same growth cycle. 相似文献
5.
Takahiro Mori Takashi Hanada Toshiharu Morimura Meoung-Whan Cho Takafumi Yao 《Current Applied Physics》2004,4(6):640-642
In this paper GaNxAs1−x surfaces during growth are observed using reflectance difference or reflectance anisotropy spectroscopy (RDS or RAS). The epi-layer was grown by solid-source molecular beam epitaxy (MBE) system with a RF nitrogen prasma source. RD spectra showed broader structure and reduced amplitude compared to those of GaAs surfaces; GaAs(2 × 4)-like features were still observed with weak and blue-shifted peaks. In the low growth temperature region, an extra structure was also observed around 3.02 eV. We proposed that GaNxAs1−x surface can be classified into three types of the surface. 相似文献
6.
The presence of parts per million (ppm) levels of impurities in the low-temperature arsenic charge used in molecular beam epitaxy (MBE) is shown to have a dramatic effect on the quality of GaAs grown. Source charge impurities play a vital role in determining the apparent variation in reported doping behaviour in MBE:GaAs. 相似文献
7.
A systematic study was performed to control the geometrical anisotropy of GaSb(As)/GaAs quantum dot structures formed by the Stranski–Krastanov growth mode of molecular beam epitaxy. In particular, effects of both the Sb4 beam flux and the As4 background pressure on the geometrical anisotropy were clarified and elongated QDs with lateral aspect ratio greater than 3 were successfully formed. Under a low As4 background pressure, As4 is found to act as surfactant to influence the adatom diffusion and change the density of QDs. By contrast, under high As4 background pressure, the intermixing of As and Sb takes place and reduces strains induced by the lattice mismatch. 相似文献
8.
A. Guillén-Cervantes Z. Rivera-Álvarez I. Koudriavtsev 《Applied Surface Science》2009,255(9):4742-4746
GaAs (1 0 0) substrates prepared in a quartz chamber under a H2/As4 flux, and then exposed to air were used for the subsequent growth of GaAs-AlGaAs single quantum wells by molecular beam epitaxy. The substrates prepared by this method showed atomically flat surfaces corroborated by atomic force microscopy analysis. Quantum wells grown directly on these substrates without a GaAs buffer layer exhibited narrow and intense photoluminescence peaks, an indication of a high quality material. The secondary ion mass spectroscopy analysis showed oxygen and carbon traces on the first AlGaAs barrier layer grown after air exposure with no effects on the quantum wells optical emissions. From the results we conclude that the prepared GaAs surfaces are useful for the epitaxial growth of high quality quantum structures. 相似文献
9.
Low-temperature photoluminescence measurements on nominally undoped AlxGa1–xAs/GaAs quantum well heterostructures (QWHs) grown by molecular beam epitaxy (MBE) exemplified the exclusivelyintrinsic free-exciton nature of the luminescence under moderate excitation conditions. Neither any spectroscopic evidence for alloy clustering in the AlxGa1–xAs barriers nor any extrinsic luminescence due to recombination with residual acceptors has been detected in single and double QWHs when grown at 670 °C under optimized MBE growth conditions. Carrier confinement in AlxGa1–xAs/GaAs QWHs starts at a well width ofL
z30 nm when x0.25. The minor average well thickness fluctuation ofL
z=4×10–2nm as determined from the excitonic halfwidth allowed the realization of well widths as low asL
z=1 nm and thus a shift of the free-exciton line as high as 2.01 eV which is close to the conduction band edge of the employed Al0.43Ga0.57As confinement layer. The measurements further revealed a strongly enhanced luminescence efficiency of the quantum wells as compared to bulk material which is caused by the modified exciton transition probabilities due to carrier localization. 相似文献
10.
Reflection medium energy electron diffraction, scanning electron microscope and measurements of angular dependence of reflectivity in vacuum ultraviolet region, low-temperature photoluminescence and Hall effect were used to study surface structure and morphology and optical and electrical properties of GaAs layers grown by molecular beam epitaxy (MBE) and influence of growth conditions on their properties. The quality of MBE GaAs layers depends strongly on the growth conditions. The residual background impurities in MBE system and other contamination sources degrade the optical and electrical quality and can influence the formation of macroscopic defects. The incorporation of background impurities and the formation of vacancy-impurity complexes are dramatically affected by As4 to Ga flux ratio at a given growth temperature and suppressed strongly under growth conditions with slight As excess which ensures to maintain the As-stabilised surface. The growth under such conditions results in improved electrical and optical properties and satisfactory surface morphology.The authors are indebted to Dr. J. Oswald for the measurements of PL spectra, to Drs. M. imecková and K. Jurek for their kind assistance in SEM investigation and for taking SEI and X-ray microprobe analyses, to Ing. O. tika for the measurements of thickness of the layers and to Dr. P. Doubrava for the Hall effect measurements in several samples. For the use of facilities to measure the Hall effect the thanks are also due to Dr. V. míd. 相似文献
11.
《Current Applied Physics》2015,15(10):1256-1261
P-type conductivity in MOCVD grown ZnO was obtained by directional thermal diffusion of arsenic from semi-insulating GaAs substrate. The films were single crystalline in nature and oriented along (002) direction. Ab initio calculations in the framework of density functional theory have been carried out with different chemical states of arsenic in ZnO. Present calculations suggested AsZn–2VZn defect is a shallow acceptor and results in ferromagnetism in ZnO. The magnetic measurements of the samples indeed showed ferromagnetic ordering at room temperature. X-ray photoelectron spectra confirmed the presence of AsZn and VZn. The core level chemical shift in binding energy of AsZn indicated the formation of AsZn–2VZn. Diffused arsenic substitutes zinc atom and creates additional zinc vacancies. The zinc vacancies, surrounding the oxygen atoms, result in unpaired O 2p electrons which in turn induce ferromagnetism in the samples. 相似文献
12.
The evaporation of GaAs under both Knudsen and Langmuir conditions has been studied using a quadrupole resonance mass spectrometer. Particular care was taken to separate beam from background signals by modulating the evaporation fluxes using a mechanical chopper. In the temperature range 850–1100°K, the arsenic vapour flux from GaAs consists mainly of As2 under both Knudsen and Langmuir conditions. Vapour pressure data for gallium and arsenic over GaAs are presented. A congruent evaporation point occurs at 898°K under Knudsen conditions. Under Langmuir conditions, GaAs evaporates congruently below 930°K but above this temperature arsenic is lost preferentially. Under Langmuir conditions constant evaporation rates were not observed from a {100} surface at any temperature studied. 相似文献
13.
A combination of the surface diagnostic techniques Auger electron spectroscopy (AES), reflection high energy electron diffraction
(RHEED), and secondary ion mass spectroscopy (SIMS) was used in order to get more detailed information on basic processes
which lead to the formation of high quality monocrystalline GaAs and Al
x
Ga1−x
As films by molecular beam epitaxy (MBE) under ultra-high vacuum conditions. The formation and changes of reconstructed surface
structures on (100) GaAs as a function of growth parameters were observedduring growth by RHEED. AES was used to determine the relative ratio of Ga/As on the surface for different reconstructed structures,
to investigate the impurity contamination on substrate surfaces and grown films, and to study the surface segregation of Sn
in MBE GaAs during doping. Finally, intentional and unintentional impurities incorporated during the growth of GaAs and Al
x
Ga1−x
As by MBE were detected by the SIMS technique immediately after growth within the reaction chamber. 相似文献
14.
ZnTe epilayers were grown on GaAs(0 0 1) substrates by molecular beam epitaxy (MBE) at different VI/II beam equivalent pressure (BEP) ratios (RVI/II) in a wide range of 0.96-11 with constant Zn flux. Based on in situ reflection high-energy electron diffraction (RHEED) observation, two-dimensional (2D) growth mode can be formed by increasing the RVI/II to 2.8. The Te/Zn pressure ratios lower than 4.0 correspond to Zn-rich growth state, while the ratios over 6.4 correspond to Te-rich one. The Zn sticking coefficient at various VI/II ratios are derived by the growth rate measurement. The ZnTe epilayer grown at a RVI/II of 6.4 displays the narrowest full-width at half-maximum (FWHM) of double-crystal X-ray rocking curve (DCXRC) for (0 0 4) reflection. Atomic force microscopy (AFM) characterization shows that the grain size enlarges drastically with the RVI/II. The surface root-mean-square (RMS) roughness decreases firstly, attains a minimum of 1.14 nm at a RVI/II of 4.0 and then increases at higher ratios. It is suggested that the most suitable RVI/II be controlled between 4.0 and 6.4 in order to grow high-quality ZnTe epitaxial thin films. 相似文献
15.
Mel’nik N. N. Zavaritskaya T. N. Kucherenko I. V. Wojtowicz T. Janik E. Plyashechnik O. S. 《Physics of the Solid State》2011,53(8):1722-1726
The spectra of resonant light scattering by ZnTe quantum wires have been measured at excitation energies of 2.18–2.72 eV.
The quantum wires have been grown on Si(100) and GaAs(100) substrates by molecular beam epitaxy. The effect of outgoing resonance
with the electron transition energy E
0 on the intensity of phonon lines of the Stokes spectrum and on the intensity ratio of the Stokes and anti-Stokes spectral
lines has been studied. The energy E
0 has been determined in ZnTe and ZnMgTe quantum wires from the edge luminescence spectra. 相似文献
16.
Well defined superlattice structures made by phase-locked epitary using RHEED intensity oscillations
T. Sakamoto H. Funabashi K. Ohta T. Nakagawa N.J. Kawai T. Kojima Y. Bando 《Superlattices and Microstructures》1985,1(4):347-352
Long continuing intensity oscillations of the RHEED pattern in the [100] azimuth on a (001) oriented substrate were observed during MBE growth of GaAs and AlxGa1−xAs. Using these oscillations, growth rates of GaAs and AlxGa1−xAs, and the Al mole fraction x of the AlxGa1−xAs were accurately monitored during the growth. The phase of the RHEED oscillations was analyzed by computer and molecular beam shutters were operated at a particular phase of the oscillations. This computer controlled phase-locked epitaxy (PLE) was used to grow precisely defined (GaAs)2(AlAs)2 bi-layer superlattices. Raman scattering spectra of the bi-layer superlattice showed split lines characteristic of superlattices. From TEM observation of a GaAs-AlAs multi-layered structure, it was verified that one cycle of oscillations corresponds to one monolayer growth of GaAs and AlAs. This PLE has a great advantage over the conventional MBE growth method for the precise control of very thin films and superlattice structures because it is invulnerable to fluctuations of molecular beam flux intensity. 相似文献
17.
18.
T. Wosiński 《Applied Physics A: Materials Science & Processing》1985,36(4):213-216
By photocapacitance technique, applied to n-type LEC-grown GaAs, two energy levels:E
v
+0.45 eV andE
c
–0.75 eV are identified, for the first time, as being associated with the EL2 trap. As follows from the analysis of photo-EPR results on highly resistive GaAs crystals, the same energy levels can be attributed to the arsenic antisite defect, AsGA. In view of these findings, it is argued that the occupied EL2 level corresponds to the neutral charge state of AsGa defect. 相似文献
19.
A bistable, self-latching inverter by the monolithic integration of resonant tunnelling diode and high electron mobility transistor 下载免费PDF全文
This paper reports that the structures of AlGaAs/InGaAs high electron mobility
transistor (HEMT) and AlAs/GaAs resonant tunnelling diode (RTD) are epitaxially
grown by molecular beam epitaxy (MBE) in turn on a GaAs substrate. An
Al0.24Ga0.76As chair barrier layer, which is grown adjacent to the top
AlAs barrier, helps to reduce the valley current of RTD. The peak-to-valley current
ratio of fabricated RTD is 4.8 and the transconductance for the 1-μm gate HEMT
is 125mS/mm. A static inverter which consists of two RTDs and a HEMT is designed and
fabricated. Unlike a conventional CMOS inverter, the novel inverter exhibits
self-latching property. 相似文献
20.
The effect of the surface preparation of the GaAs(110) substrate on the ZnSe epitaxial layer grown by molecular beam epitaxy
(MBE) was investigated by means of etch-pit density (EPD) measurements, surface morphology observation, and reflection high-energy
electron diffraction (RHEED) analysis. The ZnSe epitaxial layer grown on a GaAs(110) surface prepared by cleaving the (001)-oriented
wafer in ultrahigh vacuum (UHV) showed about 5×104 cm-2 of EPD. This value is much lower than that observed from both the samples grown on the mechanically polished surface with
and without a GaAs buffer layer. Due to the non-stoichiometric surface after thermal evaporation of the surface oxide, three-dimensional
growth can easily occur on the mechanically polished GaAs(110) substrate. These results suggest that the stoichiometric and
atomically flat substrate surface is essential for the growth of low-defect ZnSe epitaxial layers on the GaAs(110) non-polar
surface.
Received: 21 August 1998 / Accepted: 19 October 1998 / Published online: 28 April 1999 相似文献