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1.
Hot phosphoric-acid etching and atomic force microscopy (AFM) were used to etch and characterize various GaN materials, including
freestanding GaN grown by hydride vapor-phase epitaxy (HVPE), metal-organic chemical-vapor deposition (MOCVD) GaN films on
sapphire and silicon carbide, and homoepitaxial GaN films on polished freestanding-GaN wafers. It was found that etching at
optimal conditions can accurately reveal the dislocations in GaN; however, the optimal etch conditions were different for
samples grown by different techniques. The as-grown HVPE samples were most easily etched, while the MOCVD homoepitaxial films
were most difficult to etch. Etch-pit density (EPD) ranging from 4×106 cm−2 to 5×109 cm−2 was measured in close agreement with the respective dislocation density determined from transmission electron microscopy
(TEM). 相似文献
2.
G. B. Stringfellow P. F. Lindquist T. R. Cass R. A. Burmeister 《Journal of Electronic Materials》1974,3(2):497-515
Dislocations in VPE GaP grown on (100) oriented LEC GaP substrates have been characterized, and their origins and effects
on LED performance have been investigated. In non-nitrogen doped epilayers, the dislocations are found to originate in the
substrate and propagate through the epilayers in straight lines in [100] and <211> directions. The dislocation density of
the epilayer is found to be nearly equal to that of the substrate. Introduction of nitrogen during growth of the epilayer
has been observed to bend these so-called “inclined≓ dislocations propagating through the layer into [0−1 1] directions in
the (100) plane and thus produces segments of [0 −1 1] dislocations to relieve the lattice parameter mismatch due to N. The
mismatch dislocation density is observed to be proportional to the N doping level. At very high N doping levels, > 1019 cm-3, a large number of new inclined dislocations are observed, which may be in part due to GaN precipitation. The effects of
dislocations on LED properties were investigated by measuring dislocation densities in the individual diodes using the electron
beam induced current mode of the SEM and comparing this with the spot brightness and luminous flux. The dislocations were
observed to produce dark spots in the EL emission in many cases. For a series of runs where all growth and processing parameters
were fixed, a good correlation between B/J and dislocation density was observed with B/J decreasing with increasing dislocation
density in the range < 1 × 104 cm−2 to 1 × 106 cm−2. 相似文献
3.
Mg- and Si-doped GaN and AlGaN films were grown by metalorganic chemical vapor deposition and characterized by room-temperature
photoluminescence and Hall-effect measurements. We show that the p-type carrier concentration resulting from Mg incorporation
in GaN:Mg films exhibits a nonlinear dependence both on growth temperature and growth pressure. For GaN and AlGaN, n-type
doping due to Si incorporation was found to be a linear function of the silane molar flow. Mg-doped GaN layers with 300K hole
concentrations p ∼2×1018 cm−3 and Si-doped GaN films with electron concentrations n∼1×1019 cm−3 have been grown. N-type Al0.10Ga0.90N:Si films with resistivities as low as p ∼6.6×10−3 Ω-cm have been measured. 相似文献
4.
R. D. Dupuis C. J. Eiting P. A. Grudowski H. Hsia Z. Tang D. Becher H. Kuo G. E. Stillman M. Feng 《Journal of Electronic Materials》1999,28(3):319-324
Ion implantation into III–V nitride materials is animportant technology for high-power and high-temperature digital and monolithic
microwave integrated circuits. We report the results of the electrical, optical, and surface morphology of Si ion-implanted
GaN films using furnace annealing. We demonstrate high sheet-carrier densities for relatively low-dose (natoms=5×1014 cm−2) Si implants into AlN/GaN/sapphire heteroepitaxial films. The samples that were annealed at 1150°C in N2 for 5 min exhibited a smooth surface morphology and a sheet electron concentration ns ∼9.0×1013 cm−2, corresponding to an estimated 19% electrical activation and a 38% Si donor activation in GaN films grown on sapphire substrates.
Variable-temperature Hall-effect measurem entsindicate a Si donor ionization energy ∼15 meV. 相似文献
5.
Heinrich Figgemeier Martin Bruder Karl-Martin Mahlein Richard Wollrab Johann Ziegler 《Journal of Electronic Materials》2003,32(7):588-591
HgCdTe detector performance and yield are strongly dependant on CdZnTe substrate and HgCdTe epilayer properties, and on key
device processes, especially for 8–12 μm application. Due to the correlation and optimization between these figures and diode
performance, AIM has developed a mature HgCdTe technology for superior detector performance and high production rate. To meet
high yield and performance for long wavelength (LW) HgCdTe diodes, dislocation densities of < 1 × 10t cm−2 both in substrate and epilayer have to be ensured. By a unique AIM substrate growth process, dislocation densities of 2 ×
104-9 × 104 cm−2 are achieved for all substrates and epilayers (100% yield). The etch pit density (EPD) on 〈111〉 epilayers is revealed by
an AIM proprietary etching procedure. One critical effect is the dislocations in the diode area, which can originate from
the substrate and epilayer growth and the subsequent device processes, respectively. Our studies have shown that device processes
can cause additional dislocations in the diode area.
Diode yield was clearly improved by a combination of wet and dry etching for diode contact etching. 相似文献
6.
Hwe Jae Lee Soon Jae Yu Hajime Asahi Shun-Ichi Gonda Young Hwan Kim Jin Koo Rhee S. J. Noh 《Journal of Electronic Materials》1998,27(7):829-832
Ohmic contacts with low resistance are fabricated on n-GaN films using Al/Ti bilayer metallization. GaN films used are 0.3
μm thick layers with carrier concentrations of 1 × 1019 cm−3 grown on the c-plane sapphire by ion-removed electron cyclotron resonance molecular beam epitaxy. The lowest value for the
specific contact resistivity (ρc) of 1.2×10−8 Ω·cm2 was obtained with furnace annealing at 500°C for 60 min. This result shows the effectiveness of high carrier concentration
GaN layers and the low temperature annealing for the realization of low resistance ohmic contacts. Sputtering Auger electron
spectroscopy analysis reveals that Al diffuses into Ti layer and comes into contact with the GaN surface. 相似文献
7.
Microstructure and enhanced morphology of planar nonpolar m-plane GaN grown by hydride vapor phase epitaxy 总被引:1,自引:0,他引:1
Benjamin A. Haskell Arpan Chakraborty Feng Wu Hideo Sasano Paul T. Fini Steven P. Denbaars James S. Speck Shuji Nakamura 《Journal of Electronic Materials》2005,34(4):357-360
Nonpolar (
) m-plane gallium nitride has been grown heteroepitaxially on (100) γ-LiAlO2 by several groups. Previous attempts to grow m-plane GaN by hydride vapor phase epitaxy (HVPE) yielded films unsuitable for
subsequent device regrowth because of the high densities of faceted voids intersecting the films’ free surfaces. We report
here on the growth of planar m-plane GaN films on (100) γ-LiAlO2 and elimination of bulk and surface defects. The morphology achieved is smooth enough to allow for fabrication of m-plane
GaN templates and free-standing substrates for nonpolar device regrowth. The GaN films were grown in a horizontal HVPE reactor
at 860–890°C. Growth rates ranged from 30 μm/h to 240 μm/h, yielding free-standing films up to 250-μm thickness. The m-plane
GaN films were optically specular and mirror-like, with undulations having 50–200-nm peak-to-valley heights over millimeter
length scales. Atomic force microscopy revealed a striated surface morphology, similar to that observed in m-plane GaN films
grown by molecular beam epitaxy (MBE). Root-mean-square (RMS) roughness was 0.636 nm over 25-μm2 areas. Transmission electron microscopy (TEM) was performed on the m-plane GaN films to quantify microstructural defect densities.
Basal-plane stacking faults of 1×105 cm−1 were observed, while 4×109 cm−2 threading dislocations were observed in the g=0002 diffraction condition. 相似文献
8.
J. F. Ocampo B. Bertoli P. B. Rago E. N. Suarez D. Shah F. C. Jain J. E. Ayers 《Journal of Electronic Materials》2010,39(4):391-399
We report an experimental and modeling study of ZnS
y
Se1−y
/GaAs (001) structures, all of which comprised a uniform top layer of ZnS0.014Se0.986 grown on a compositionally graded buffer layer or directly on the GaAs substrate. High-resolution x-ray diffraction was used
to estimate dislocation densities on type A slip systems, with misfit dislocation (MD) line segments oriented along the [1[`1]0] [1\bar{1}0] direction, and type B slip systems, with MD line segments oriented along a [110] direction. A control sample having no graded
buffer exhibits equal dislocation densities on the two types of slip systems (D
A ≈ D
B ≈ 1.5 × 108 cm−2), but a forward-graded (FG) structure (grading coefficient of 27 cm−1) exhibits 20% more dislocations on the type B slip systems (D
A ≈ 1.6 × 108 cm−2 and D
B ≈ 1.9 × 108 cm−2) and a steep forward-graded structure (grading coefficient of 54 cm−1) exhibits 50% more type B dislocations (D
A ≈ 2 × 108 cm−2 and D
B ≈ 3 × 108 cm−2). The insertion of an overshoot interface reduced the dislocation densities in the uniform top layer by promoting annihilation
and coalescence reactions, but type B dislocations were removed more effectively. Based on equilibrium calculations the overshoot
graded layer in the steep graded overshoot structure is expected to exhibit large compressive and tensile strains, with a
reversal in the sign of the strain near its middle, which may promote annihilation and coalescence reactions between threading
dislocations. 相似文献
9.
E. Dimakis E. Iliopoulos M. Kayambaki K. Tsagaraki A. Kostopoulos G. Konstantinidis A. Georgakilas 《Journal of Electronic Materials》2007,36(4):373-378
The molecular beam epitaxy of In-face InN (0001) epilayers with optimized surface morphology, structural quality, and electrical
properties was investigated. Namely, compact InN epilayers with atomically flat surfaces, grown in a step-flow mode, were
obtained using stoichiometric fluxes of In and N and substrate temperatures in the range from 400°C to 435°C. Typical values
for the electron concentration and the Hall mobility at 300 K were 4.3 × 1018 cm−3 and 1210 cm2/Vs, respectively. The growth mode of InN during the very first stage of the nucleation was investigated analytically, and
it was found that the growth proceeds through nucleation and fast coalescence of two-dimensional (2-D)–like InN islands. The
preceding conditions were used to grow an InN/GaN quantum well (QW) heterostructure, which exhibited well-defined interfaces.
Schottky contacts were successfully fabricated using a 15-nm GaN barrier enhancement cap layer. Capacitance-voltage measurements
revealed the confinement of electrons within the InN QW and demonstrated the capability to modulate the electron density within
an InN channel. The sheet concentration of the confined electrons (1.5 × 1013 cm−2) is similar to the calculated sheet polarization charge concentration (1.3 × 1013 cm−2) at the InN/GaN interface. However, electrons may also originate from ionized donors with a density of 8 × 1018 cm−3 within the InN layer. 相似文献
10.
Pulsed laser deposition and processing of wide band gap semiconductors and related materials 总被引:1,自引:0,他引:1
R. D. Vispute S. Choopun R. Enck A. Patel V. Talyansky R. P. Sharma T. Venkatesan W. L. Sarney L. Salamancariba S. N. Andronescu A. A. Iliadis K. A. Jones 《Journal of Electronic Materials》1999,28(3):275-286
The present work describes the novel, relatively simple, and efficient technique of pulsed laser deposition for rapid prototyping
of thin films and multi-layer heterostructures of wide band gap semiconductors and related materials. In this method, a KrF
pulsed excimer laser is used for ablation of polycrystalline, stoichiometric targets of wide band gap materials. Upon laser
absorption by the target surface, a strong plasm a plume is produced which then condenses onto the substrate, kept at a suitable
distance from the target surface. We have optimized the processing parameters such as laser fluence, substrate temperature,
background gas pressure, target to substrate distance, and pulse repetition rate for the growth of high quality crstalline
thin films and heterostructures. The films have been characterized by x-ray diffraction, Rutherford backscattering and ion
channeling spectrometry, high resolution transmission electron microscopy, atomic force microscopy, ultraviolet (UV)-visible
spectroscopy, cathodoluminescence, and electrical transport measurements. We show that high quality AlN and GaN thin films
can be grown by pulsed laser deposition at relatively lower substrate temperatures (750–800°C) than those employed in metal
organic chemical vapor deposition (MOCVD), (1000–1100°C), an alternative growth method. The pulsed laser deposited GaN films
(∼0.5 μm thick), grown on AlN buffered sapphire (0001), shows an x-ray diffraction rocking curve full width at half maximum
(FWHM) of 5–7 arc-min. The ion channeling minimum yield in the surface region for AlN and GaN is ∼3%, indicating a high degree
of crystallinity. The optical band gap for AlN and GaN is found to be 6.2 and 3.4 eV, respectively. These epitaxial films
are shiny, and the surface root mean square roughness is ∼5–15 nm. The electrical resistivity of the GaN films is in the range
of 10−2–102 Θ-cm with a mobility in excess of 80 cm2V−1s−1 and a carrier concentration of 1017–1019 cm−3, depending upon the buffer layers and growth conditions. We have also demonstrated the application of the pulsed laser deposition
technique for integration of technologically important materials with the III–V nitrides. The examples include pulsed laser
deposition of ZnO/GaN heterostructures for UV-blue lasers and epitaxial growth of TiN on GaN and SiC for low resistance ohmic
contact metallization. Employing the pulsed laser, we also demonstrate a dry etching process for GaN and AlN films. 相似文献
11.
K.K. Allums M. Hlad A.P. Gerger B.P. Gila C.R. Abernathy S.J. Pearton F. Ren R. Dwivedi T.N. Fogarty R. Wilkins 《Journal of Electronic Materials》2007,36(4):519-523
Proton irradiation of Sc2O3/GaN and Sc2O3/MgO/GaN metal-oxide semiconductor diodes was performed at two energies, 10 MeV and 40 MeV, and total fluences of 5 × 109 cm−2, corresponding to 10 years in low-earth orbit. The proton damage causes a decrease in forward breakdown voltage and a flat-band
voltage shift in the capacitance-voltage characteristics, indicating a change in fixed oxide charge and damage to the dielectric.
The interface state densities after irradiation increased from 5.9 × 1011 cm−2 to 1.03 × 1012 cm−2 in Sc2O3/GaN diodes and from 2.33 × 1011 to 5.3 × 1011 cm−2 in Sc2O3/MgO/GaN diodes. Postannealing at 400°C in forming gas recovered most of the original characteristics but did increase the
interfacial roughness. 相似文献
12.
A. E. Wickenden D. D. Koleske R. L. Henry R. J. Gorman M. E. Twigg M. Fatemi J. A. Freitas Jr. W. J. Moore 《Journal of Electronic Materials》2000,29(1):21-26
Growth pressure has a dramatic influence on the grain size, transport characteristics, optical recombination processes, and
alloy composition of GaN and AlGaN films. We report on systematic studies which have been performed in a close spaced showerhead
reactor and a vertical quartz tube reactor, which demonstrate increased grain size with increased growth pressure. Data suggesting
the compensating nature of grain boundaries in GaN films is presented, and the impact of grain size on high mobility silicon-doped
GaN and highly resistive unintentionally doped GaN films is discussed. We detail the influence of pressure on AlGaN film growth,
and show how AlGaN must be grown at pressures which are lower than those used for the growth of optimized GaN films. By controlling
growth pressure, we have grown high electron mobility transistor (HEMT) device structures having highly resistive (105 Ω-cm) isolation layers, room temperature sheet carrier concentrations of 1.2×1013 cm−2 and mobilities of 1500 cm2/Vs, and reduced trapping effects in fabricated devices. 相似文献
13.
R. P. Tompkins J. R. Smith K. W. Kirchner K. A. Jones J. H. Leach K. Udwary E. Preble P. Suvarna J.M. Leathersich F. Shahedipour-Sandvik 《Journal of Electronic Materials》2014,43(4):850-856
We have examined the performance of gallium nitride (GaN) high-power Schottky diodes fabricated on unintentionally doped (UID) metalorganic chemical vapor deposition (MOCVD) films grown simultaneously on four substrates ranging in threading dislocation density from 5 × 103 cm - 2 to 1010 cm - 2. The substrates were an intentionally doped and a UID freestanding hydride vapor phase epitaxy substrate, an MOCVD GaN template grown on a sapphire wafer, and a bulk GaN substrate grown via an ammonothermal method. Capacitance–voltage (C–V) results showed the carrier concentration was ~2 × 1016 cm?3 for films grown on each of the four substrates. With that doping level, the theoretical breakdown voltage (V b) is ~1600 V. However, measured V b for the devices tested on each of the four substrates fell short of this value. Also, the breakdown voltages across each of the four substrates were not substantially different. This result was especially surprising for films grown on bulk GaN substrates, because of their superior crystal quality, as determined from their x-ray rocking curve widths. Simple probability calculations showed that most of the diodes tested on the bulk substrate did not cover a single threading dislocation. Although optimization of edge-termination schemes is likely to improve V b, we believe that point defects, not threading dislocations, are the main reason for the reduced performance of these devices. 相似文献
14.
As a first step towards developing heterostructures such as GaAs/Ge/Si entirely by chemical vapor deposition, Ge films have
been deposited on (100) Si by the pyrolysis of GeH4. The best films are grown at 700° C and are planar and specular, with RBS minimum channeling yields of ≈4.0% (near the theoretical
value) and defect densities of 1.3 x 108 cm−2. Variations of in-situ cleaning conditions, which affect the nature of the Si substrate surface, greatly affect the ability
to get good epitaxial growth at 700° C. The majority of the defects found in the Ge films are extrinsic stacking faults, formed
by dissociation of misfit and thermal expansion accommodation dislocations. The stacking fault density is not significantly
reduced by post-deposition annealing, as is the case for the dislocations observed in MBE Ge films. It is suggested that lowering
the CVD growth temperature through the use of high vacuum deposition equipment would result in dislocation defects like those
of MBE films which could then be annealed more effectively than stacking faults. Films with defect densities equivalent to
MBE Ge films (~2 x 107 cm−2) could then probably be produced. 相似文献
15.
采用条形Al掩模在Si(111)衬底上进行了GaN薄膜侧向外延的研究.结果显示,当掩模条垂直于Si衬底[11-2]方向,也即GaN[10-10]方向时,GaN无法通过侧向生长合并得到表面平整的薄膜;当掩模条平行于Si衬底[11-2]方向,也即GaN[10-10]方向时,GaN侧向外延速度较快,有利于合并得到平整的薄膜.同时,研究表明,升高温度和降低生长气压都有利于侧向生长.通过优化生长工艺,在条形Al掩模Si(111)衬底上得到了连续完整的GaN薄膜.原子力显微镜测试显示,窗口区域生长的GaN薄膜位错密度约为1×109/cm2,而侧向生长的GaN薄膜位错密度降低到了5×107/cm2以下. 相似文献
16.
The impact of nitridation and nucleation layer process conditions on morphology and electron transport in GaN epitaxial films 总被引:1,自引:0,他引:1
A. E. Wickenden D. D. Koleske R. L. Henry R. J. Gorman J. C. Culbertson M. E. Twigg 《Journal of Electronic Materials》1999,28(3):301-307
A systematic study has been performed to determine the characteristics of an optimized nucleation layer for GaN growth on
sapphire. The films were grown during GaN process development in a vertical close-spaced showerhead metalorganic chemical
vapor deposition reactor. The relationship between growth process parameters and the resultant properties of low temperature
GaN nucleation layers and high temperature epitaxial GaN films is detailed. In particular, we discuss the combined influence
of nitridation conditions, V/III ratio, temperature and pressure on optimized nucleation layer formation required to achieve
reproducible high mobility GaN epitaxy in this reactor geometry. Atomic force microscopy and transmission electron microscopy
have been used to study improvements in grain size and orientation of initial epitaxial film growth as a function of varied
nitridation and nucleation layer process parameters. Improvements in film morphology and structure are directly related to
Hall transport measurements of silicon-doped GaN films. Reproducible growth of silicon-doped GaN films having mobilities of
550 cm2/Vs with electron concentrations of 3 × 1017 cm−3, and defect densities less than 108 cm−2 is reported. These represent the best reported results to date for GaN growth using a standard two-step process in this reactor
geometry. 相似文献
17.
M. A. Sánchez-García E. Calleja F. J. Sanchez F. Calle E. Monroy D. Basak E. Muñoz C. Villar A. Sanz-Hervas M. Aguilar J. J. Serrano J. M. Blanco 《Journal of Electronic Materials》1998,27(4):276-281
GaN layers have been grown by plasma-assisted molecular beam epitaxy on AlN-buffered Si(111) substrates. An initial Al coverage
of the Si substrate of aproximately 3 nm lead to the best AlN layers in terms of x-ray diffraction data, with values of full-width
at half-maximum down to 10 arcmin. A (2×2) surface reconstruction of the AlN layer can be observed when growing under stoichiometry
conditions and for substrate temperatures up to 850°C. Atomic force microscopy reveals that an optimal roughness of 4.6 nm
is obtained for AlN layers grown at 850°C. Optimization in the subsequent growth of the GaN determined that a reduced growth
rate at the beginning of the growth favors the coalescence of the grains on the surface and improves the optical quality of
the film. Following this procedure, an optimum x-ray full-width at half-maximum value of 8.5 arcmin for the GaN layer was
obtained. Si-doped GaN layers were grown with doping concentrations up to 1.7×1019 cm−3 and mobilities approximately 100 cm2/V s. Secondary ion mass spectroscopy measurements of Be-doped GaN films indicate that Be is incorporated in the film covering
more than two orders of magnitude by increasing the Be-cell temperature. Optical activation energy of Be acceptors between
90 and 100 meV was derived from photoluminescence experiments. 相似文献
18.
X. A. Cao R. G. Wilson J. C. Zolper S. J. Pearton J. Han R. J. Shul D. J. Rieger R. K. Singh M. Fu V. Scarvepalli J. A. Sekhar J. M. Zavada 《Journal of Electronic Materials》1999,28(3):261-265
Donor (S, Se, and Te) and acceptor (Mg, Be, and C) dopants have been implanted into GaN at doses of 3–5×1014 cm−2 and annealed at tem peratures up to 1450°C. No redistribution of any of the elements is detectable by secondary ion mass
spectrometry, except for Be, which displays behavior consistent with damageassisted diffusion at 900°C. At higher temperatures,
there is no further movement of the Be, for peak annealing temperature durations of 10 s. Effective diffusivities are ≤2×10−13 cm2·s−1 at 1450°C for each of the dopants in GaN. 相似文献
19.
This paper describes the effect of Al doping (0 at.% to 6 at.%) on the structural and optoelectronic properties of nanocrystalline
ZnO thin films deposited by thermal evaporation. X-ray diffraction patterns confirm that an increase in Al concentration (from
0% to 6%) in ZnO lowers the crystallinity of the films and reduces grain size. Al doping is also found to influence the optical
properties of the ZnO thin films. Visible transmittance above 85% was obtained by increasing the Al doping to 6%. The optical
bandgap was found to vary from 3.20 eV to 3.97 eV with changing Al content from 0% to 6%, which is in accordance with the
Burstein–Moss shift. The mobility of ZnO thin films can be varied from 5.60 cm2/Vs to 24.25 cm2/Vs, the carrier concentration from 5.93 × 1018/cm3 to 9.11 × 1020/cm3, and the resistivity from 4.62 × 10−4 Ω cm to 4.34 × 10−2 Ω cm, depending on the Al doping concentration (0% to 6%). This study suggests that ZnO:Al films can be tailor-made to meet
the requirements for various optoelectronic applications such as flexible photocells or ultraviolet (UV) photodetectors covering
a wide range of short wavelengths. 相似文献
20.
Intentionally undoped and three different, doped layer structures are used to investigate properties of AlGaN/GaN high electron
mobility transistors (HEMTs) before and after SiN passivation. For unpassivated devices, the drain current, transconductance,
cutoff frequency, and microwave output-power increase with increased doping level, in spite of an increase in the gate-leakage
current. After passivation, an overall performance improvement of all devices occurs. The passivation-induced sheet charge
decreases from 2×1012 cm−2 in undoped structures to ∼0.7×1012 cm−2 in higher doped structures and performance improvement with passivation is less pronounced for higher doped devices. However,
the output power of unpassivated and passivated devices on higher doped structures is much higher than that on the undoped-passivated
counter-part. These results underline an advantage of the doped layer structure for the preparation of high-performance AlGaN/GaN
HEMTs. 相似文献