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1.
D. C. Look G. D. Robinson J. R. Sizelove C. E. Stutz 《Journal of Electronic Materials》1993,22(12):1425-1428
We use the Hall effect and a new charge-transfer technique to study molecular beam epitaxial GaAs grown at the low substrate
temperatures of 300–450°C. Layers grown from 350–450°C are semi-insulating (resistivity greater than 107 Ω-cm), as grown, because of an AsGa-related donor (not EL2) at EC-0.65 eV. The donor concentrations are about 2×1018 cm−3 and 2×1017 cm−3 at growth temperatures of 300 and 400°C, respectively, and acceptor concentrations are about an order of magnitude lower.
Relatively high mobilities (∼5000 cm2/V s) along with the high resistivities make this material potentially useful for certain device applications. 相似文献
2.
We report 0.8 eV photoluminescence (PL) emission of GaAs grown at low temperatures between 325 and 400°C by molecular beam
epitaxy. Effects of heat treatments of the 0.8 eV emission are compared with those of the 1.467 eV sharp bound exciton lines.
This allows us to attribute the 0.8 eV emisson to the As-VGa center. We discuss the assigning of the Asi-VGa center to the well-known EL6. The PL intensity variation of 0.68 eV EL2 and 0.8 eV Asi-VGa seen in substrate materials is explained in terms of dislocation−mediated Asi-VGa transformation to EL2 whereas the PL intensity variation of 0.8 eV Asi-VGa for molecular beam epitaxy layers can be attributed to the growth condition. 相似文献
3.
We have utilized a variable energy positron beam and infrared transmission spectroscopy to study defects in GaAs epilayers
grown at low temperatures (LT-GaAs) by molecular beam epitaxy. We have measured the Doppler broadening of the positron-electron
annihilation gamma ray spectra as a function of positron implantation energy. From these measurements, we have obtained results
for the depth profiles of Ga monovacancies in unannealed LT-GaAs and Ga monovacancies and arsenic cluster related defects
in annealed LT-GaAs. We have also studied the effects of the Si impurities in annealed LT-GaAs. The infrared transmission
measurements on unannealed LT-GaAs furnish a broad defect band, related to As antisites, centered at 0.370 eV below the conduction
band. 相似文献
4.
Hall and drift mobilities in molecular beam epitaxial grown GaAs 总被引:1,自引:0,他引:1
V. W. L. Chin T. Osotchan M. R. Vaughan T. L. Tansley G. J. Griffiths Z. Kachwalla 《Journal of Electronic Materials》1993,22(11):1317-1321
A series of nominally undoped and Si-doped GaAs samples have been grown by molecular beam epitaxy (MBE) with Hall concentrations
ranging from 1015 to 1019 cm−3 and mobilities measured at 77 and 300K by Hall-van der Pauw methods. Drift mobilities were calculated using the variational
principle method and Hall scattering factors obtained from a relaxation-time approximation to permit cross-correlation of
experimental data with drift or Hall mobilities and actual or Hall electron concentrations. At 77K, both high purity and heavily
doped samples are well represented by either drift or Hall values since piezoelectric acoustic phonon scattering and strongly
screened ionized impurity scattering hold the Hall factor close to unity in the respective regimes. Between n≊1015 and 1017 cm−3, where lightly screened ionized impority scattering predominates, Hall mobility overestimates drift mobility by up to 50
percent and Hall concentration similarly underestimates n. At 300K, polar optical phonons limit mobility and a Hall factor
up to 1.4 is found in the lowest doped material, falling close to unity above about 1016 cm−3. Our calculation also agrees remarkably well with the Hall mobility of the highest purity MBE grown sample reported to date. 相似文献
5.
Current transport in molecular beam epitaxy (MBE) GaAs grown at low and intermediate growth temperatures is strongly affected
by defects. A model is developed here that shows that tunneling assisted by defect states can dominate, at some bias ranges,
current transport in Schottky contacts to unannealed GaAs material grown at the intermediate temperature range of about 400°C.
The deep defect states are modeled by quantum wells which trap electrons emitted from the cathode before re-emission to semiconductor.
Comparison of theory with experimental data shows defect states of energies about 0.5 eVbelow conduction band to provide the
best fit to data. This suggests that arsenic interstitials are likely to mediate this conduction. Comparison is also made
between as-grown material and GaAs grown at the same temperature but annealed at 600°C. It is suggested that reduction of
these defects by thermal annealing can explain lower current conduction at high biases in the annealed device as well as higher
current conduction at low biases due to higher lifetime. Quenching of current by light in the as-grown material can also be
explained based on occupancy of trap states. Identification of this mechanism can lead to its utilization in making ohmic
contacts, or its elimination by growing tunneling barrier layers. 相似文献
6.
D. N. Talwar M. O. Manasreh C. E. Stutz R. Kaspi K. R. Evans 《Journal of Electronic Materials》1993,22(12):1445-1448
Samples of molecular beam epitaxial GaAs grown at low temperatures doped with Be defects are studied as a function of growth
temperature (TG)-by measuring their localized vibrational modes at 77K using BOMEM Fourier transform infrared spectrometer. Localized vibrational
modes of9BeGa in samples grown at TG>350°C have been identified at 482 cm−1. Secondary ion mass spectroscopy measurements show that the densities of Be defects remain approximately constant as TG is lowered, however, additional structure in the9BeGa localized vibrational mode is observed. Calculations based on Green's function theory suggest that the additional structure
in Be-doped LT GaAs can best be explained in terms of a complex center [9BeGa-AsGa] involving an intrinsic defect. 相似文献
7.
We report the diffusion of zinc into low temperature (LT) GaAs grown by MBE at 200° C, the problems associated with using a silicon nitride film directly deposited on the LT GaAs as a Zn diffusion mask, and several schemes to avoid the problems. The Zn diffusion coefficient is measured (sealed-ampoule technique) to be about one order of magnitude higher in the LT GaAs than in normal GaAs, attributed to a large quantity of defects including arsenic antisites (AsGa) in the LT GaAs. The effectiveness of silicon nitride as a Zn diffusion mask depends if the mask is deposited directly on the LT GaAs. The failure of the nitride directly deposited on the LT GaAs to stop the Zn is attributed to arsenic atoms outdiffusing from the As-rich LT GaAs (about 1 at. % excess As) into the nitride. Several structures are introduced including a 100-Å thick GaAs layer on the LT GaAs that are effective in preserving the diffusion mask properties of the silicon nitride. 相似文献
8.
GaAs selective epitaxial growth by conventional molecular beam epitaxy (MBE) was studied while varying its growth conditions,
such as substrate temperature. As pressure, growth rate, and Si or Be doping. Selectivity is improved with the increase in
substrate temperature, and with the decrease in As pressure or growth rate. Si and Be were doped up to 3 x 1018 and 3 × 1019 cm−3, respectively. While no Si doping influence was observed, Be doping degraded the surface morphology. Selective epitaxial
growth by conventional MBE with appropriate growth conditions will be applicable to device fabrication. 相似文献
9.
M. S. Han T. W. Kang J. H. Leem B. K. Song Y. B. Hou W. H. Baek M. H. Lee J. H. Bahng K. J. Kim J. M. Kim H. K. Kim T. W. Kim 《Journal of Electronic Materials》1997,26(6):507-510
Spectroscopic ellipsometry and photoreflectance measurements on CdTe/GaAs strained heterostructures grown by moleculclr beam
epitaxy were carried out to investigate the effect of the strain and the dependence of the lattice parameter on the CdTe epitaxial
layer thicknesses. Compressive strains exist in CdTe layers thinner than 2 μm. As the strain increases, the value of the critical-point
energy shift increases linearly. These results indicate that the strains in the CdTe layers grown on GaAs substrates are strongly
dependent on the CdTe layer thickness.
Author to whom all correspondence should be addressed. 相似文献
10.
In this paper,we discuss low-temperature hopping-conductivity behavior in the insulating phase,in the absence of a magnetic field.We conduct a theoretical study of the crossover from hopping to activated transport in a GaAs two-dimensional hole system at low temperatures,finding that a crossover takes place from the Efros-Shklovskii variable-range hopping (VRH) regime to an activated regime in this system.This conductivity behavior in p-GaAs quantum wells is qualitatively consistent with the laws laid down in theories of localized electron interactions.Given sufficiently strong interactions,the holes in the localized states are able to hop collectively. 相似文献
11.
Hopping conduction in heavily doped bulk n-type SiC 总被引:1,自引:0,他引:1
W. C. Mitchel A. O. Evwaeaye S. R. Smith M. D. Roth 《Journal of Electronic Materials》1997,26(3):113-118
The electronic properties of heavily doped n-type 4H, 6H, and 15R SiC have been studied with temperature dependent Hall effect,
resistivity measurements, and thermal admittance spectroscopy experiments. Hopping conduction was observed in the resistivity
experiments for samples with electron concentrations of 1017 cm−3 or higher. Both band and hopping conduction were observed in all three polytypes in resistivity and Hall effect experiments.
The hopping conduction activation energy ε3 obtained from the resistivity measurements varied from 0.003 to 0.013 eV. The ε3 value obtained from thermal admittance spectroscopy measurements were slightly lower. The nitrogen ionization levels were
observed by thermal admittance spectroscopy only in those samples where hopping conduction was not detected by this experiment.
Free carrier activation energy Ea for nitrogen was difficult to determine from temperature dependent Hall effect measurements because of the effects of hopping
conduction. A new feature in the apparent carrier concentration vs inverse temperature data in the hopping regime was observed. 相似文献
12.
Optoelectronic modulation spectroscopy (OEMS) has been used to examine defect-related states in GaAs metal-semiconductor,
field-effect transistor (MESFET) structures prepared by molecular-beam epitaxy (MBE) on buffer layers formed at normal and
low temperatures. The technique was used to simultaneously observe the spectra of defect states near to the interface with
the buffer layer and in the active layer. There were few responses that were common to the structures. The most prominent
was an electron trap with a depth of 0.92 eV. This was present throughout both structures and may be from a native defect
in GaAs. With few exceptions the states seen in a particular structure were present in the active layer as well as near to
the interface with the buffer layer suggesting that, in each case, the defects originated from the active/buffer layer interface
or from the buffer layer. The most significant difference was that states in the low-temperature (LT)-based structure generally
exhibited replicating responses with specific energy periodicities. A model describes this in terms of optical-absorption
transitions to the local vibrational states of defects. Five different replica series were observed. The vibrational characteristics
of the defects found in the LT material suggest that they are different in character and extent to those defects found in
material formed on a normally prepared buffer layer. Their Frank-Condon energies ranged from 9–332 meV. 相似文献
13.
Electrical properties of low-temperature GaAs grown by molecular beam epitaxy and migration enhanced epitaxy 总被引:1,自引:0,他引:1
Measurements on low-temperature GaAs epitaxial layers (LT-GaAs) grown by molecular beam epitaxy and migration enhanced epitaxy
showed that the excess arsenic incorporated during growth played a crucial role in determining their electrical properties.
The electrical transport in LT-GaAs grown by a standard molecular beam epitaxy proceeded mainly via a hopping process, which
showed a higher activation energy and onset temperature than those usually observed in lightly doped semiconductors. Using
migration enhanced epitaxy to grow LT-GaAs, we were able to substantially reduce the density of As-rich defects and to achieve
a good Hall mobility in Be-doped LT-GaAs. The study presented here indicates that, with controlled excess arsenic incorporation
during growth, LT-GaAs can vary in a range of conduction properties and thus can be engineered for different device applications. 相似文献
14.
R. S. Berg Nergis Mavalvala Tracie Steinberg F. W. Smith 《Journal of Electronic Materials》1990,19(11):1323-1330
Raman scattering measurements on high-resistivity layers of GaAs grown by molecular beam epitaxy at low temperature are presented.
Several defect-related features are ob-served, including two peaks attributed to quasi-localized vibrational modes of point
de-fects, one with a frequency of 223 cm−1 similar to a mode previously observed in elec-tron-irradiated GaAs, and the other with a frequency of 47 cm−1 similar to a mode observed in ion-implanted GaAs. We suggest that these are due to arsenic interstitials and gallium vacancies,
respectively. We also observe peaks at 200 and 258 cm−1, which we believe may be due to vibrational modes in small clusters of arsenic. The 223 cm−1 mode is the only defect-related mode still observed after a 10-min annealing treatment at 600° C, although it is significantly
broader and has different symmetry from the 223 cm−1 mode in the unannealed material. This indicates that the 223 cm−1 mode in the annealed material is due, at least in part, to a defect other than the arsenic interstitial. 相似文献
15.
Conductive Be doped GaAs grown by molecular beam epitaxy at low substrate temperatures (300° C) was obtained for the first
time by using migration enhanced epitaxy (MEE) without subsequent annealing. The layers were characterized using Hall effect,
double crystal x-ray diffraction, and photoluminescence. With low arsenic exposure, the low temperature MEE layers doped with
Be had the same carrier density and similar luminescent efficiency as layers grown by conventional MBE at 580° C. Mobility
at 77 K was reduced somewhat for layers doped at 2 × 1017cm−3, which also exhibited hopping conductivity below 40 K. Double crystal x-ray diffraction showed that low temperature MEE samples
grown at low As exposure had the narrow linewidth associated with conventional MBE material grown at 580° C, unlike layers
grown by conventional MBE at low temperatures, which exhibit an expansion in lattice parameter. 相似文献
16.
The photo-induced current transient spectroscopy (PICTS), thermoelectric effect spectroscopy (TEES) and thermally stimulated
current (TSC) spectroscopy have been used to characterize the deep levels in the GaAs materials grown at low temperature by
molecular beam epitaxy. At least five hole traps and five electron traps have been identified by the TEES measurement employing
a simplified sample arrangement. We have studied the behavior of various traps as a function of the growth temperature and
the post-growth annealing temperature. Some of the shallower hole traps were annealed out above 650‡ C. Electron traps atE
c- 0.29 eV andE
c- 0.49 eV were present in the material, and have been identified as M3 and M4, respectively. The dominant electron trap, atE
c- 0.57 eV, is believed to be associated with the stoichiometric defect caused by the excess As in the material, and our data
show evidence of forming a defect band by this trap. A possible model involving As precipitates is proposed for this trap
atE
c-0.57 eV. 相似文献
17.
V. Mahadev M. R. Melloch J. M. Woodall N. Otsuka G. L. Liedl 《Journal of Electronic Materials》1994,23(10):1015-1020
High resolution x-ray diffraction using synchrotron radiation was used to characterize GaAs grown by MBE at low temperatures
(LT-GaAs) LT-GaAs grown at 225°C is nonstoichiometric and exhibits a 0.15% lattice expansion along the growth direction. Annealing
LT-GaAs results in arsenic clusters with a well-defined orientation relationship with the GaAs matrix and a relaxation of
the LT-GaAs lattice. The arsenic precipitation corresponds to a classical case of diffsion controlled nucleation and growth
followed by coarsening. While the rates of growth and coarsening in the n-doped and the p-doped samples are observed to be
identical, the effects of the superlattice seem to accelerate the precipitation kinetics in the p-n superlattice sample. The
enhanced coarsening in the p-n superlattice sample is consistent with a previously propsed model involving interaction between
charged precipitate and arsenic defects. 相似文献
18.
We report on the realization of a modified delta doping technique to obtain doping profiles in MBE grown GaAs, measured by capacitance-voltage (C-V) methods with full-widths at half-maximum (FWHM)s of 25 ± 5Å and peak concentrations of up to 1.1 × 1019 cm?3. In this modified delta doping technique, both the Ga and Si shutters were opened for 15 sec during the delta doped layer growth while only the Si shutter is opened during conventional delta doping. Comparison of the two techniques under the same dopant flux and shutter-open-time interval shows that higher sheet-carrier concentrations with narrower FWHMs and higher peak concentrations are obtained with the modified delta doping than with the conventional delta doping method. This suggests that Si donor incorporation is enhanced by the Ga adatoms while broadening of the Si donor distribution is still negligible for this short time interval. The effects of the substrate temperature and the shutter-open time on the Si donor distribution have also been investigated. 相似文献
19.
Based on micrographic as well as experimental analyses, we show that particulates which inadvertently adhere to the surface
before the wafer is ready for growth are one of the most significant origins for the formation of oval defects on the GaAs
layers grown by molecular beam epitaxy. We show that the density of surface particulates is proportional to that of airborne
particles surrounding the wafer under preparation, especially during the drying and transferring process. With reduction of
airborne particles, we simultaneously reduce the density of oval defects from a few thousand to about 200 cm-2 for 1-μm thick layers. 相似文献
20.
本文研究了斜切割(100)Ge衬底上InxGa1-xAs/GaAs量子阱结构的分子束外延生长(In组分为0.17或者0.3)。所生长的样品用原子力显微镜、光致发光光谱和高分辨率透射电子显微镜进行了测量和表征。结果发现,为了生长没有反相畴的GaAs缓冲层,必须对Ge衬底进行高温退火。在GaAs外延层和InxGa1-xAs/GaAs量子阱结构的生长过程中,生长温度是一个至关重要的参数。文中讨论了温度对于外延材料质量的影响机理。通过优化生长温度,Ge衬底上的InxGa1-xAs/GaAs量子阱结构的光致发光谱具有很高的强度、很窄的线宽,样品的表面光滑平整。这些研究表面Ge 衬底上的III-V族化合物半导体材料有很大的器件应用前景。 相似文献