bluuebunny/crossref_metadata_2025 huggingface dataset:
Low Temperature Growth of GaAs and AlGaAs by Mombe
Authors: Abernathy C. R. , Bohling D. A. , Jones A. C.
Published: March 2011

We have examined various methods of overcoming the problems of low growth efficiency and high carbon uptake which occur when GaAs is grown at low temperatures by Metal Organic Molecular Beam Epitaxy (MOMBE). We have found that removal of the carbon through conventional means such as precracking or interaction with hydrogen is not effective in enhancing the carbon removal process. In fact, the use of a hydrogen plasma during growth actually increases the carbon background due to a reduction in the surface V/III ratio. Greater success is obtained when alternative precursors are used as replacements for AsH3 and triethylgallium (TEG). Tris-dimethylaminoarsenic (DMAAs) offers reduced carbon uptake through formation of amine compounds while tri-isobutylgallium (TTBG) shows better efficiency and less carbon than TEG at low growth temperature.
Wet and Dry Etching of InGaP
Authors: Lothian J. R. , Kuo J. M. , Pearton S. J. , Ren F.
Published: March 2011

The wet chemical etching rates of InGaP in H3 PO4:HCL:H2O mixtures have been systematically measured as a function of etch formulation and are most rapid (-1 μm · min−1) for high HCl compositions. The etch rate, R, in a 1:1:1 mixture is thermally activated of the form R ∝ e−Ea/kT, where Ea = 11.25 kCal · mole−1. This is consistent with the etching being reaction-limited at the surface. This etch mixture is selective for InGaP over GaAs. For chlorine-based dry etch mixtures (PCl3 /Ar or CCl2 F2 /Ar) the etching rate of InGaP increases linearly with DC self-bias on the sample, whereas CH4/H2-based mixtures produce slower etch rates. Selectivities of ≥500 for etching GaAs over InGaP are obtained under low bias conditions with PCl3/Ar, but the surface morphologies of InGaP are rough. Both CCl2F2/Ar and CH4/H2/Ar mixtures produce smooth surface morphologies and good (>10) selectivities for etching GaAs over InGaP.
Anisotropic Reactive Ion Etching of Submicron W Features In CF4 or SF6 Plasmas
Authors: Fullowan T. R. , Ren F. , Pearton S. J. , Mahoney G. E. , Kostelak R. L.
Published: March 2011

Anisotropie RIE etching of Tungsten (W) in a low voltage CF4 or SF6 plasma while achieving features as small as 0.50 μm is demonstrated using Titanium (Ti) as an etch mask. For reasons of reliability and tolerance to high temperature processing techniques, W can be a desirable contact metal in microelectronics fabrication. Due to its high melting point (3400°C) it is not practical to evaporate W contacts using conventional liftoff photolithography methods. Therefore pattern transfer of sputtered W must be performed by plasma etching using some type of mask. In III-V materials systems, a Fluorine based plasma is desirable due to its high selectivity for W over semiconductor materials. The problem is that when using conventional photoresist masks, W does not etch anisotropically. Therefore critical feature dimensions (which are sub-micron for FET gates) and vertical profiles cannot be successfully transferred to the underlying W. However by using a Ti mask during the CF4 or SF6 plasma etch, TiF4 is produced on the sidewalls of the W inhibiting any horizontal etch. The Ti mask can be removed selectively after etching of the W is complete. Using a Ti mask to etch W ensures excellent pattern transfer of device dimensions even at very low bias voltage.
Low Damage Magnetron Reactive Ion Etching of GaAs
Authors: Mclane G. , Meyyappan M. , Cole M. W. , Lee H. S. , Lareau R. , Namaroff M. , Sasserath J.
Published: March 2011

Magnetron reactive ion etching is an attractive alternative to reactive ion etching since it has the potential for producing minimal surface damage while still retaining the advantages of reactive ion etching. We report here the results of a study of GaAs magnetron ion etching using Freon-12 and silicon tetrachloride etch gases. Differences are found in etch profiles and surface region characteristics of GaAs samples etched by the two gases. The relevant mechanisms are discussed.
The Use of Tertiarybutylphosphine and Tertiarybutylarsine for the Metalorganic Molecular Beam Epitaxial Growth of Resonant Tunneung Devices
Authors: Beam E. A. , Seabaugh A. C.
Published: March 2011

We report on the use of thermally-cracked tertiarybutylphosphine (TBP) and tertiarybutylarsine (TBA) with elemental Ga, In, and Al sources for the MOMBE growth of InP-based resonant tunneling diode (RTD) and resonant tunneling bipolar transistor (RTBT) structures. We have systematically examined the effects of growth conditions and heterostructure modifications on the InP/lnGaAs RTD including the use of pseudomorphic (InGa)P barriers and, in addition, explored for the first time, InP quantum well RTDs using both AlAs and InGaP barriers. Cross-sectional transmission electron microscopy has been used to correlate the structural quality with the electrical characteristics for both lattice-matched and pseudomorphic layers composed of InAs, AlAs, and InGaP. We also demonstrate the first use of mixed InP/lnGaAs and AlAs/lnGaAs heterojunctions in the RTBT. These transistors exhibit room temperature negative transconductance and a peak-to-valley current ratio of 35, the highest yet observed In the RTBT.
Multichamber Rie Processing for Ingaasp Ridge Waveguide Laser Arrays
Authors: Rothman Mark A. , Thompson John A. , Armiento Craig A.
Published: March 2011

The fabrication of devices based on III-V materials often requires a number of different reactive ion etching (RIE) processes that must be implemented sequentially. These processes are typically carried out in different RIE systems to avoid cross contamination. In this paper, we describe a multichamber RIE system configured to provide several sequential etch processes required for the fabrication of optoelectronic devices. This system has been used to fabricate InGaAsP/lnP ridge waveguide laser arrays with etched mechanical features that enable passive alignment of the lasers with single-mode fibers. Laser arrays with threshold currents as low as 20 mA have been processed with a high degree of uniformity. This system has also been used to develop a laser facet etch process based on CH4/H2/Ar chemistry. This process has been used to fabricate lasers with monolithically integrated rear facet monitors. These etched facet lasers have threshold currents comparable to lasers with both facets cleaved.
An Etch-Back Planarization Process Using A Sacrificial Polymide Layer
Authors: Lothian J. R. , Fullowan T. R.
Published: March 2011

An etch-back polymide planarization process for the emitter contact of AlGaAs/GaAs HBTs using PC-1500 is presented. The degree of surface topography has a major impact on the yield in HBT fabrication. A planarization process using a spin-on sacrificial layer to produce a planar interlevel dielectric layer would be very beneficial in allowing thicker and more uniform emitter contacts therefore enhancing the yield and current handling capability. The PC-1500 polymer flows at 200°C and provides a much better planarity than regular photoresist. For patterns from -3 μm to 250 this polymer can achieve 80% to 92% planarity. The wafers were etched in a parallel plate, single wafer reactive ion-etching system with a mixture of oxygen and Freon-14. The etch rate of this polymer increased with the oxygen content of the discharge then became fairly constant at high O2 concentrations while the etch rate of the underlying dielectric film (SiN) was proportional to the Freon 14 content. This new polymer shows little loading effect. A 1:1 etch rate ratio of SiN to PC-1500 was established for good planarity.
Reactive Ion Etching of TaSix in a CF4-O2 Discharge
Authors: Chen C. P. , Din K. S. , Huang F. S.
Published: March 2011

In the self-alignment technology for GaAs MESFET, the pattern technique for refractory suicide gate is needed. Reactive ion etching (RIE) of TaSix on GaAs has been performed in a mixture of CF4 and O2 Etching properties have been studied as function of oxygen percentage, total pressure and power. The samples were then examined in Scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) to understand the surface morphology and constitution. It is found that the etch rate of TaSixincreased with increasing oxygen percentage initially, reached a maximum value near 10∼15% O2, then started to decrease with increasing oxygen at applied power 100 watt, pressure 50 mtorr, and total gas flow 40 seem. This etch rate also increases with RF power and total pressure in CF4 + O2 15% gas at gas flow rate 40 sccm. For GaAs etching, the rate is independent of oxygen percentage. This etch rate of GaAs also increases with power, but decreases with total pressure. Meanwhile, the SEM micrograph shows no undercut for sample after RIE at the applied power 140 watt with the pressure of 20 mtorr.
Use of Pt Gate Metallization to Reduce Gate Leakage Current in GaAs MESFETs
Authors: Ren F. , Emerson A. B. , Pearton S. J. , Hobson W. S. , Fullowan T. R. , Lothian J.
Published: March 2011

The use of wet-chemical removal of native oxide in a sealed nitrogen ambient prior to deposition of metal on GaAs is shown to be an effective method of engineering the Schottky barrier height of the metal contacts. Due to its higher metal work function, a barrier height of 0.98 eV for Pt on n-type GaAs is demonstrated. This is considerably higher than the barrier height of conventionally processed TiPtAu contacts (0.78 eV). MESFETs fabricated using PtAu bilayer contacts show reverse currents an order of magnitude lower than TiPtAu contacted companion devices, higher reverse breakdown voltages and much lower gate leakage. Utilizing this technology of oxide removal and the PtAu bilayer contact provides a much simpler method of enhancing the barrier height on n-type GaAs than other techniques such as counter-doping the near-surface or inserting an interfacial layer.
Sintered Ohmic Contacts to GaAs
Authors: Cibuzar Gregory T.
Published: March 2011

The formation of reliable low resistance ohmic contacts to GaAs and other III-IV compound semiconductors is essential for useful device and circuit fabrication. We have modified the standard AuGe ohmic contact process by using rapid thermal annealing at temperatures less than the AuGe eutectic temperature to form contacts based on sintering rather than alloying. Compared with alloyed contacts, sintered contacts have similar electrical performance, superior morphology, and improved reliability. Results from secondary mass spectroscopy analysis of sintered and alloyed contacts will be discussed.
Quasi-Schottky Diodes on (n)In.53Ga.47as with Barrier Heights of 0.6 eV
Authors: Marso M. , Kordoš P. , Meyer R. , Lüth H.
Published: March 2011

The modification and control of the Schottky barrier height on (n)InGaAs is an important tool at the device preparation as the barrier height is very low, øB° = 0.2 eV. We report about the Schottky barrier enhancement on (n)InGaAs by thin fully depleted surface layers of high doped (p+)InGaAs. Structures with different thicknesses of (p+)InGaAs in the range from 8 to 80 nm were grown by LP MOVPE technique and quasi-Schottky diodes with different contact areas were prepared using titanium as a barrier metal. I-V and I-T characteristics were measured and analysed to obtain basic parameters of prepared diodes, i. e. ideality factor n, effective barrier height øB, series resistance Rgand reverse current density JR (1V). The barrier height enhancement increases with the thickness of the (p+)-layer. Effective barrier heights of øB>0.6 eV, i.e. higher than reported until now, can be obtained with the surface layers of (p+)InGaAs with thicknesses exceeding 25 nm.
Temperature Dependent Schottky Contacts to InP and GaAs
Authors: Shi Z. Q. , Wallace R. L. , Anderson W. A.
Published: March 2011

The barrier height of a Pd/n-InP diode was found to be increased from 0.48 to 0.96eV with the substrate temperature decreased from 300 to 77K during metal deposition. The leakage current density was reduced by more than six order of magnitude. It is obvious that the interface Fermi-level position lies well outside the variance associated with Fermi-level pinning. The barrier height for the Au/n-GaAs diode was found to be increased by about 0.25 eV with low temperature deposition and the leakage current reduced by more than five orders of magnitude. The mechanism responsible for the ultrahigh barrier height obtained at low substrate temperature was investigated by Raman spectroscopy, current voltage temperature measurement, deep level transient spectroscopy, and electroreflectance technique. The metal-insulator-semiconductor (MIS)-like structure formed at low substrate temperature and the reduction of interface state density may be the main reason for the dramatic enhancement of Schottky barrier height.
Stable Schottky Contacts to n-Type GaAs Produced by Ge Rich Co-Ge Metalization
Authors: Koltin E. , Eizenberg M.
Published: March 2011

Interfacial reactions between thin films of cobalt and germanium on (001) oriented GaAs substrates were studied in two configurations, Co/Ge/GaAs and Ge/Co/GaAs, with emphasis on Ge rich stoichiometries. It was found that at low temperatures, 250≤T<350δC, cobalt reacted with germanium to form intermetallie compounds which depended on the Co/Ge atomic ratio, while the inner interface with the GaAs substrate remained intact. At higher temperatures (up to 600δC) a limited reaction with the GaAs substrate was detected. This reaction was contained for both configurations near the interface with the substrate, and did not develop with temperature. The extent of reaction decreased with the decrease in the Co:Ge atomic ratio. Contacts produced in these systems were rectifying with a nearly ideal thermionic emission behavior.
A Novel GaAs Bipolar Transistor Structure with GaInP-Hole Injection Blocking Barrier
Authors: Pletschen W. , Bachem K. H. , Lauterbach T.
Published: March 2011

GaAs bipolar transistors of different emitter types have been fabricated from MOCVD grown lattice matched Ga0.5In0.5 P/GaAs layer structures using carbon for heavy base doping (p=2×1019 cm−3). Besides conventional heterojunction bipolar transistors we also investigated tunneling emitter bipolar transistors having 2 and 5 nm thin GalnP layers between emitter and base, which act as a hole repelling potential barrier in the valence band. Current gains up to 115 have been obtained at collector current densities of 104 A/cm2 even for this heavy base doping. All devices show an almost ideal output characteristics with large Early voltage and small offset voltage. From the temperature dependence of the collector current a small effective conduction band barrier at the heterointerface is determined which hardly affects electron injection into the base.
High-Performance Structure of Light-Emitting Diode for GaAs on Si Tetsuroh Minemura
Authors: Asano Junko , Yazawa Yoshiaki
Published: March 2011

The Light-emitting diode (LED) structures have been investigated to realize high-performance LEDs on Si substrates. The light intensity of the LEDs with p-GaAs / n-GaAs / Si structures, which was effected from thickness of the p-GaAs layer, was only about 55% of the homoepitaxialLED. The light intensity of the LED with an n-GaAs/p-GaAs/Si structure, however, was about four times stronger than those of p-GaAs/n-GaAs/Si structures. After continuous operation for two hours, the intensity still kept much stronger than those of the LEDs with p-GaAs / n-GaAs / Si structures, although it decreased to 15% of the homoepitaxial LED.
Integrated Distributed Feedback Laser and Optical Amplifier
Authors: Dutta N. K. , Lopata J. , Logan R. , Tanbun-Ek T.
Published: March 2011

The fabrication and performance characteristics of an integrated distributed feedback (DFB) laser and optical amplifier structure are described. The structure utilizes semi-insulating Fe doped InP layers for current confinement to the active region, electrical isolation between the two sections and for lateral index guiding. The amplified output has a slope of 1 mW/mA of laser current with the amplifier biased at 150 mA which is a factor of 5 larger than that for a typical laser. The laser emits near 1.55 μm and the spectral width under modulation of the amplified output is considerably smaller than that for a DFB laser for the same on/off ratio.
The Effect of Rapid Thermal Annealing on the Electrical and Material Characteristics of Planar Doped and Uniformly Doped GaAs/AiGaAs/InGaAs Pseudomorphic HEMT Structures
Authors: Kazior T. E. , Brierley S. K.
Published: March 2011

MBE grown GaAs/Al0.25Ga0.75As/In0.85Ga0.85 As structures were subjected to SiNx capped rapid thermal annealing and their electrical and material properties were characterized by Hall measurements and photoluminescence (PL). Low temperature (5°K) PL spectra from undoped structures annealed up to 900°C indicated negligible intermixing at the AIGaAs/lnGaAs interface. For planar doped structures (Nd≈5×1012/cm2) the Hall mobility began to decrease at anneal temperatures as low as 800°C with significant degradation observed for annealing temperatures at 850°C. This data is supported by PL spectra which indicate no significant change for samples annealed at 800°C. For the samples annealed at ≥ 850°C a large increase in the full width at half maximum of the transitions from the electron sub-bands of the InGaAs quantum well were observed, suggesting that the change in electrical characteristics is primarily due to diffusion of the Si doping pulse. In contrast. Hall measurement of uniformly doped structures reveal only small decreases in mobility and no significant change in sheet concentration for anneal temperatures up to 900°C and doping levels up to 2.5×1018/cm3. PL spectra reveal no structural changes.
P-Type Quantum Well Infrared Photodetectors Grown by OMVPE
Authors: Hobson W. S. , Zussman A. , De Jong J. , Levine B. F.
Published: March 2011

We report on the growth and fabrication of p-doped long wavelength GaAs/AlxGa1−x As quantum well infrared photodetectors (QWIP) grown by organometallic vapor phase epitaxy. The operation of these devices is based on the photocurrent induced through valence band intersubband absorption by holes and, unlike n-doped QWIPs, can utilize normal incidence illumination. Carbon and zinc were used as the p-type dopants in a low-pressure (30 Torr) vertical-geometry reactor. The Zn-doped QWIP consisted of fifty periods of 48 nm-thick undoped Al0.36Ga0.64As barriers and nominally 4 nm-thick doped GaAs quantum wells. Using normal incidence, a quantum efficiency of η = 2.5% and a detectivity of at 77K were obtained for a peak wavelength λp = 6.8 μm and a cutoff wavelength λ∫ =7.6 μm. The C-doped QWIP had 54 nm-thick Al0.31Ga0.69As barriers and exhibited a normal incidence These initial studies indicate the superiority of carbon to zinc as the p-type dopant for these structures. The detectivity of the C-doped QWIPs is about four times less than n-doped QWIPs for the same λp but have the advantage of utilizing normal incidence illumination.
Growth of GaAs and AlGaAs by MOMBE Using Phenylarsine
Authors: Abernathy C. R. , Wisk P. , Pearton S. J. , Ren F. , Bohling D. A. , Muhr G. T.
Published: March 2011

Because of the extreme toxicity ofA3, it is highly desirable to employ gaseous As sources which contain fewer As-H bonds. Attempts to introduce compounds such as tertiarybutylarsine (TBAs) during growth by metal-organic molecular beam epitaxy (MOMBE) have been somewhat unsuccessful due to the need for pre-cracking of these materials, and to the extreme reactivity of the hydrocarbon radicals released upon their decomposition. These byproducts have been found to severely degrade various components in the growth system, and could lead to enhanced carbon uptake at low growth temperatures. Phenylarsine (PhAs) offers several advantages over the more common As substitutes as it has been demonstrated to decompose at growth temperatures of ≥575°C, and the byproducts of its decomposition are expected to be far less reactive than the byproducts of the other As precursors.

In this paper we will discuss the growth of GaAs and AlGaAs at low growth temperatures (≤530°C) using PhAs as the As source. In this temperature range, the III-V growth rate is restricted due to the cracking efficiency of the PhAs. For example, at 530°C, a PhAs flow rate of ∼5.4 seem limits the growth rate to ∼95 Å/ min while a similar flow of AsH3 through a low pressure cracker allows for deposition at rates >250 Å/min. Further comparisons of the two As sources will be discussed regarding their effect on GaAs and AlGaAs growth rates from triethylgallium, trimethylgallium, and trimethylamine alane, and their effect on carbon and oxygen impurity incorporation.
Interface Recombination and Threshold Current in Grinsch-QW ALGaAs/GaAs Laser Diodes
Authors: Xie K. , Kim H. M. , Wie C. R. , Varriano J. A. , Wicks G. W.
Published: March 2011

A series of Graded-Index Waveguide Separate-Confinement Heterostructure Quantum Well (GRINSCH-QW) laser diodes were grown by MBE at the systematically varied substrate temperatures. The threshold current of laser diodes were found to depend strongly on the growth temperature. The structure and electrical characteristics of the laser diodes were studied by double-crystal x-ray diffraction, I-V-T, C-V and deep level transient spectroscopy (DLTS). The interface recombination is found to be the dominant carrier transport process in the high threshold current laser diodes and is closely related to the presence of the high concentration of deep traps and interface states. In the low threshold current laser diodes, diffusion process is found to be the dominant carrier transport process.
AlAs-GaAs Beterojunction Engineering by Means of Group IV Interface Layers
Authors: Bratina G. , Sorba L. , Biasiol G. , Vanzetti L. , Franciosi A.
Published: March 2011

Valence and conduction band discontinuities in AlAs-GaAs heterostruc-tures have been tuned through fabrication of epitaxial Ge layers at the interface. The local interface dipole associated with the Ge layer can be added to, or subtracted from the natural band offsets depending on the growth sequence. Comparison with earlier results for AlAs-Si-GaAs heterostructures, shows that the observed dipole is consistent in direction and order of magnitude for Ge and Si interface layers. The dipole initially increases with interface layer thickness more rapidly for Ge than for Si, however the total maximum dipole achievable at the interface is identical (0.4eV), within experimental uncertainty, for the two group IV elements.
High Performance Quantum Well Asymmetric Fabry-Perot Reflection Modulators: Effect of Layer Thickness Variations
Authors: Law K-K. , Whitehead M. , Merz J. L. , Coldren L. A.
Published: March 2011

We present a study of the effects of the active cavity layer thickness variation on the operating characteristics of normally-on low-voltage high performance asymmetric Fabry-Perot modulators. For a modulator consisting of 25.5 periods of a multiple-quantum-well active region (100Å GaAs / 45Å (GaAs/AlAs) short period superlattices) with 5 pairs and 20.5 pairs of top and bottom quarter-wave stacks respectively, assuming only layer thickness variation in the active cavity caused by Ga flux nonuniformity, the shift of the Fabry-Perot mode wavelength is ∼5.8 times that of the QW heavy-hole exciton. This affects the relative distance between the wavelengths of the quantum well exciton and the Fabry-Perot resonance, and hence the performance of the modulators. Also, the tolerable percentage change of the Fabry-perot mode wavelength should be less than 0.13% in order that such modulator arrays have at least 10:1 contrast ratios at a fixed optimum operating wavelength. This defines the epitaxial growth tolerance for obtaining the uniformity of the operating wavelength of an array and the precision with which we can obtain a desired wavelength, its reproducibility, and its uniformity across a wafer.
Simulation Design and Device Characteristics of AlAs/GaAs/AlAs Resonant Tunneling Structures with a GalnAs Emitter Spacer Layer
Authors: Choi Y. W. , Kim H. M. , Wie C. R.
Published: March 2011

Electrical and structural investigation of AlAs/GaAs/AlAs resonant tunneling structures with pseudomorphic strained Ga1−xInxAs (x=0, 0.05, 0.1, 0.15, and 0.2) emitter spacer layer are presented. As indium composition increased, the peak current density, peak voltage, and peak to valley ratio increased. For a theoretical understanding of these increases, a self-consistent simulation was employed. In the simulation, we treated the 2-dimensional electrons confined in the low energy bandgap GalnAs emitter spacer well as pseudo-3-dimensional electrons, distributed continuously down to the emitter launching energy. In the simulation, we used the bottom energy of the pseudo-3-dimensional electrons to be ⅔δEc below the emitter conduction band edge. Using the above values, an excellent agreement of peak current density and peak voltage between the experiment and the simulation was achieved. Also, for structural identification, standard double crystal x-ray rocking curve technique has been used. From the interference analysis of the x-ray results, we could obtain the indium composition times thickness product.
Dependence of Interdiffusion in AlGaAs on Stoichiometry between Ga-RICH and As-Rich Solidus Limits
Authors: Olmsted B. L. , Houde-Walter S. N. , Viturro R. E.
Published: March 2011

Al-Ga interdiffusion of undoped AlGaAs/GaAs multiple quantum wells was studied by varying the crystal defect concentrations and is shown to be mediated predominantly by column III vacancies from the Ga-rich to the As-rich side of the solidus. An increase of two orders of magnitude has been observed in the interdiffusion coefficient when going from the inclusion of excess Ga to excess As in the evacuated ampoule. The in-diffusion of column HI vacancies from the surface in an As-rich ambient, as well as the out-diffusion of column III vacancies from the n-type substrate in an As-poor ambient, were observed using secondary ion mass spectroscopy. The role of SiO2 and Si3N4 encapsulations in controlling the interdiffusion was also determined. We have also observed that the photoluminescence intensity in the Ga-rich crystal is several orders of magnitude stronger than that of the As-rich crystal. Finally, cathodoluminescence spectroscopy reveals a deep level which has been associated with a Ga vacancy complex in the samples annealed with excess As that correlates with the extent of Al-Ga intermixing.
Effect of Surface Ambient on Manganese Diffusion in Gallium Arsenide
Authors: Wu C. H. , Hsieh K. C.
Published: March 2011

Data are presented showing the effects of diffusion sources, surface encapsulation, and As overpressure on Mn diffusion in GaAs. Four different Mn-containing sources are used, including Mn, Mn,MN3As, and MnAs granules as well as Mn thin film deposited directly onto GaAs substrate. Smooth surface morphology with high surface Mn concentration can be obtained using MnAs (and in certain conditions, Mn3As) as diffusion source; different degrees of surface degradation are observed if otherwise sources are used as diffusion source. Data also show surface encapsulation and As overpressure have significant effects on the reaction between the source and GaAs and the Mn diffusion in GaAs.
The Effect of Co-Implantation on the Electrical Activity of Implanted Carbon in GaAs
Authors: Moll A. J. , Walukiewicz W. , Yu K. M. , Hansen W. L. , Haller E. E.
Published: March 2011

We have undertaken a systematic study of the effect of co-implantation on the electrical properties of C implanted in GaAs. Two effects have been studied, the additional damage caused by co-implantation and the stoichiometry in the implanted layer. A series of co-implant ions were used: group III (B, Al, Ga), group V (N, P, As) and noble gases (Ar, Kr). Co-implantation of ions which create an amorphous layer was found to increase the electrical activity of C Once damage was created, maintaining stoichiometric balance by co-implantation of a group III further increased the fraction of electrically active carbon impurities. Co-implantation of Ga and rapid thermal annealing at 950°C for 10 s resulted in carbon activation as high as 68%, the highest value ever reported.
Damage Related Defect Levels in Oxygen Implanted GaAs and InP
Authors: He L. , Anderson W. A.
Published: March 2011

Oxygen ion-implantation can be used to create high resistivity regions in GaAs and InP. We have studied the low dose oxygen implantation in GaAs and InP by photoreflectance spectroscopy (PR), deep level transient spectroscopy (DLTS) and current-voltage (I-V) characteristics. Rapid thermal annealing (RTA) treatments were carried out at different temperatures after implantation to study the annealing temperature effect. The surface disturbance by implantation was studied by PR. Free carrier compensation was observed in every implanted sample and gave improved I-V properties. By DLTS tests, one electron trap with Ea = Ec-0.15eV and a hole trap with Ea = Ev + 0.76eV in the starting GaAs wafer disappeared after O+ implantation due to carrier compensation. In undoped InP, three new electron traps with Ea = Ec-0.47eV, 0.28eV and O.lleV were created after O+ implantation which are believed to be damage related. The comparison of the results from undoped and n-type doped InP indicated that the carrier compensation effect is substrate doping dependent.
The Effect of Si Planar Doping on DX Centers in Al.20Ga.74As
Authors: Solomon G. S. , Roos G. , Muñoz-Merino E. , Harris J. S.
Published: March 2011

The effect of planar Si doping on the DX center in AlGaAs is investigated using Capacitance-Voltage and Deep Level Transient Spectroscopy techniques. We observe an increase of approximately six orders of magnitude in the DX center capture cross section in Al.26Ga.74As with planar doped Si spikes of 2×1012cm−2 as compared to conventional homogeneous Si doped Al.26Ga.74As. We also observe a small increase in the DX activation energy which was initiated at a lower planar doping of 4×1011 cm−2 and remained constant for the higher planar doping case. We believe the DX center concentration is not changed by the planar doping levels studied here. A model is proposed to explain the increase in capture cross section based on a biaxial stress state in the planar doped AlGaAs region.
Crystal Structure Of Lt Gaas Layers Before And After Annealing
Authors: Liliental-Weber Zuzanna
Published: March 2011

The structural quality of GaAs layers grown at low temperatures by solid-source and gassource MBE at different growth conditions is described. Dependence on the growth temperature and concentration of As [expressed as As/Ga beam equivalent pressure (BEP)] used for the growth is discussed. A higher growth temperature is required to obtain the same monocrystalline layer thickness with increased BEP The annealing of these layers is associated with the formation of As precipitates. Semicoherent precipitates with lowest formation energies arc formed in the monocrystalline parts of the layers grown with the lowest BEP. Precipitates with higher bormation energies are formed when higher BEP is applied; they are also formed in the vicinity of structural defects. Formation of As precipitates releases strain in the layers. Arsenic precipitates are not formed in annealed ternary (InAlAs) layers despite their semi-insulating properties. The role of As precipitates in semi-insulating properties and the short lifetime of minority carriers in these layers is discussed.
Defect Model and Growth Characteristics of Low Temperature GaAs
Authors: Fatemi M. , Tadayon B. , Dietrich H. B. , Tadayon S.
Published: March 2011

Low-temperature GaAs layers (LTGaAs) grown by molecular beam epitaxy on GaAs substrates have been characterized by x-ray diffraction techniques. X-ray rocking curve measurements on more than 200 anneal conditions show that through appropriate choice of growth condition, layers with different states of strain are obtained. Three distinct ranges of low temperature growth are defined, labelled as “low-range,” “mid-range,” and “high-range,” corresponding to growth temperatures less than 260 °C, between 260 and 450 °C, and more than 450 °C, respectively. 0.5μm thick films grown in the low-range are amorphous, whereas those in the mid-range are fully strained and lattice-matched to the substrate, and those grown above 450 °C are indistinguishable from ordinary GaAs. Notable properties of mid-range layers are the random behavior of the as-grown strain, and the expansion and contraction of the lattice parameter with thermal anneals up to 900 °C. A growth model for LTGaAs based on arsenic antisite defects is proposed.
Long Wavelength Characterization of Internal Quantum Efficiency in LT-GaAs MSM Photodiodes
Authors: Morse Jeffrey D. , Mariella Raymond P.
Published: March 2011

Metal-Semiconductor-Metal (MSM) photodiodes fabricated from low temperature (LT) grown GaAs by molecular beam epitaxy have been characterized for wavelengths extending out to 1.5μm. External quantum efficiencies on the order of 0.5 % have been measured for subbandgap wavelengths, which translates to internal quantum efficiencies of 2–4 % for the interdigitated electrode structure with lμm finger spacing and width. Although the effective lifetime of the LT-GaAs has been determined to be <1ps, an MSM photodiode response of ∼10ps full width at half maximum was measured by correlation techniques at 820 nm wavelength, and a system limited response of 3GHz was measured at 1.3 μm wavelength. These experimental results will be described in detail.
A New Structure for a Superconducting Field Effect Transistor
Authors: Tyč Stéphane , Schuhl Alain
Published: March 2011

A new structure is proposed and described which can solve the most severe drawbacks of current architectures for Josephson FETs. Its advantages are discussed, and several realizations are suggested.
Incorporation of Silicon in Low Temperature Molecular Beam Epitaxial GaAs
Authors: Manasreh M. O. , Evans K. R. , Stutz C. E. , Look D. C , Hemsky J.
Published: March 2011

The localized vibrational mode (LVM) of silicon donor (SiGa) in molecular beam epitaxial GaAs layers grown at various temperatures is studied using the infrared absorption technique. It is found that the total integrated absorption of this LVM is decreased as the growth temperature decreases. This finding suggests a nonsubstitutional incorporation of Si in GaAs layers grown at ∼200 °C. On the other hand, an almost complete substitutional incorporation is obtained in GaAs layers grown at temperatures higher that 350 °C. Thermal annealing does not cause any recovery of the SiGa LVMs in present GaAs layers grown at ∼200°C.
Structural and Defect Study of Low Temperature INP Grown by Gas Source Molecular Beam Epitaxy
Authors: Garcia J. Ch. , Hirtz J. P. , Maurel P. , Von Bardeleben H. J. , Bourgoin J. C.
Published: March 2011

The low temperature growth procedure used in the case of GaAs to introduce high concentrations of deep traps such as arsenic antisite defects has been extended to the growth of InP by gas source molecular beam epitaxy. The low temperature growth of InP induces a strong group V stoechiometric deviation (of the order of +1%). On the other hand, Secondary Ion Mass Spectrometry reveals high levels of hydrogen ranging from 3.1018 to 3.1019 cm−3 depending on growth temperature. Undoped layers are found to be resistive without any post annealing. Annealing experiments above 250°C lead to conductive layers suggesting a passivation effect of both shallow donors and acceptors by hydrogen.
Optically Detected Magnetic Resonance of Arsenic Antisites in GaAs MBE Layers Grown at Low Temperatures
Authors: Rong F. C. , Fotiadis L. , Sun H.-J. , Watkins G. D. , Taysing-Lara M. A. , Flemish J. , Chang W. H.
Published: March 2011

Observation of Arsenic antisites (AsGa) in GaAs layers grown by molecular beam epitaxy (MBE) at low substrate temperatures (∼ 200°C) is reported, using electron paramagnetic resonance (EPR), magnetic circular dichroism in absorption (MCDA), and MCDA tagged by optically detected magnetic resonance (MCDA-ODMR). This experiment confirms that there is a MCD absorption band directly associated with AsGa in the GaAs layers. The AsGa concentration in the GaAs layers is found to decrease by about one order of magnitude after annealing at 600°C for two minutes.
Photoreflectance and X-Ray Photoelectron Spectroscopy in Lt MBE GaAs
Authors: Look D. C. , Hoelscher J. E. , Grant J. T. , Stutz C. E. , Evans K. R. , Numan M.
Published: March 2011

It has recently been shown that a 1000Å cap layer of molecular beam epitaxial (MBE) GaAs grown at 200°C passivates the surface of a GaAs active layer (n≃2×1017cm−3) in the sense of reducing the free–carrier depletion which arises from surface acceptor states. The same phenomenon holds for active-layer concentrations up to 7×1018cm−3, for caps as thin as 14Å, and for either As2 or As4 anion species. In an attempt to understand these effects, we have applied photoreflectance (PR) and x–ray photoelectron spectroscopy (XPS). In general, the PR shows contributions from the surface, cap/active–layer interface, and active–layer/buffer–layer interface, because each of these regions can have a different electric field. In fact the various field strengths can be determined from Franz–Keldysh oscillations (FKO), and good agreement with Hall–effect measurements is usually found. However, for 200°C material, no PR is seen, suggesting that there is no surface charge (no surface acceptor states below the Fermi level) or at least no surface–charge modulation by the light. The XPS data, which arise only from the near–surface (∼30Å) region, show that the binding energies in the capped samples are increased (i.e., surface Fermi pinning energy decreased) by 0.2 eV with respect to those in the uncapped samples. These data are discussed in relation to a passivation model.
Fluorine Atom Addition to the Diamond (111) Surface
Authors: Freedman Andrew , Robinson Gary N. , Stinespring Charter D.
Published: March 2011

Diamond (111) surfaces with the dehydrogenerated 2×1 reconstruction have been exposed to a beam of atomic fluorine at 300 K. The uptake of fluorine, as measured using X-ray photoelectron spectroscopy, is quite efficient and saturates at a coverage of less than a monolayer. Low energy electron diffraction patterns indicate that fluorine termination of the diamond surface produces a lxi bulk-like reconstruction in contrast to the disordered surface produced on the (100) surface.
Characterization of the Si/Diamond Interface
Authors: Williams K. E. , Speck J. S. , Drory M. D.
Published: March 2011

Auger spectroscopy is used to determine the bonding states of carbon in the interfacial region between silicon and PECVD diamond films. SiC and sp2-hybridized carbon are observed. We suggest a possible growth sequence for diamond films to account for the interfacial layer.
Optical Evidence of Reduction of Radiative Defects in Diamond Films Grown by Acetylene-Oxygen Flames
Authors: Freitas J. A. , Strom U. , Doverspike K. , Marks C. M. , Snail K. A.
Published: March 2011

Raman scattering and photoluminescence spectroscopies have been used to characterize polycrystalline diamond films deposited on molybdenum substrates by laminar and turbulent premixed oxygen-acetylene flames in air. Samples deposited under laminar flame conditions are characterized by a high degree of incorporation of nitrogen-vacancy complexes. However, samples deposited with a turbulent flame show a significant decrease in the concentration of these defects and a reduction of the amorphous carbon film component.
Tantalum and Tantalum Silicide High Temperature Rectifying Contacts on Type MB Natural Diamond
Authors: Sahaida Scott R. , Thompson Dale G.
Published: March 2011

Tantalum and tantalum suicide contacts were investigated as high temperature rectifying contacts on type MB natural diamond. Tantalum and silicon were co-sputtered using DC and RF planar magnetrons, respectively. Current-voltage measurements of tantalum suicide subjected to various anneals and of pure tantalum contacts were recorded at 50°C intervals up to 400°C which was the desired operating temperature of the rectifying contact. Tantalum contacts to diamond maintained good rectification up to 300°C whereas amorphous tantalum suicide operated well up to 400°C.
Chemical Vapor Deposition of Diamond Films Using Water:Alcohol:Organic-Acid Solutions
Authors: Rudder R. A. , Posthill J. B. , Hudson G. C. , Malta D. P. , Thomas R. E. , Markunas R. J. , Humphreys T. P. , Nemanich R. J.
Published: March 2011

A low pressure chemical vapor deposition technique using water-alcohol vapors has been developed for the deposition of polycrystalline diamond films and homoepitaxial diamond films. The technique uses a low pressure (0.50 – 1.00 Torr) rf-induction plasma to effectively dissociate the water vapor into atomic hydrogen and OH. Alcohol vapors admitted into the chamber with the water vapor provide the carbon balance to produce diamond growth. At 1.00 Torr, high quality diamond growth occurs with a gas phase concentration of water approximately equal to 47% for methanol, 66% for ethanol, and 83% for isopropanol. A reduction in the critical power necessary to magnetically couple to the plasma gas is achieved through the addition of acetic acid to the water.alcohol solution. The lower input power allows lower temperature diamond growth. Currently, diamond depositions using water:methanol:acetic-acid are occurring as low as 300 ° C with only about 500 W power input to the 50 mm diameter plasma tube.
High Quality Epitaxial Films of ZnSe and ZnSe/ZnS Strained Layer Superlattices Grown by MOCVD
Authors: Pong Chungdee , DeMattei R. C. , Feigelson R. S.
Published: March 2011

High quality epitaxial films of ZnSe and ZnSe/ZnS strained layer superlattices (SLS) have been grown on (100) GaAs substrates using diethylZinc, dimethylSelenide, diethylSelenide, and propyleneSulfide as reagents in both atmospheric and low pressure environment. This source combination produces the results showing the influence of process conditions, such as reagent flow ratio (fv1/f11) and substrate temperature, on the film stoichiometry, surface morphology, and crystalline quality. Low temperature photoluminescence (PL), Rutherford backscattering spectrometry (RBS), cross-sectional TEM, and x-ray diffraction have been used to characterize the films. Photoluminescence studies at 2.8 K on samples of ZnSe/ZnS strained layer superlattices; 10 periods ZnSe(1.5 nm)/ZnS(8.5 nm), have shown quantum size effect with the peak energy blue-shifted to 3.03 eV with the FWHM=73 meV. Atomic force microscopy (AFM) was applied to study surface morphology of multilayer samples.
The Application of Lamma-1000 to the Elemental Analysis of CdTe Compound
Authors: Belogorokhov A. I. , Khar'Kovsky A. Yu.
Published: March 2011

Data from numerous LMMS analysis of specimens of a polished sample of CdTe crystal are treated statistically to estimate the accuracy and reproducibility of quantitative analysis. The data are consistent with the instrument producing a fixed condition in plasma for a given laser power. The plasma chemistry is shown to control the conditions reached in the plasma for a given power.
Theory of Doping of Diamond
Authors: Bernholc J. , Kajihara S. A. , Antonelli A.
Published: March 2011

Electronic applications of diamond require control over native defects as well as the ability to dope it p- and n-type. B is an excellent p-type dopant, but n-type doping has proven very difficult. Diamond films have also been very difficult to anneal, indicating a high activation energy for self-diffusion. We have investigated the properties of native defects and impurities through large-scale band structure and Car-Parrinello calculations. We indeed find that the activation energy for self-diffusion is very high in the intrinsic material, but it decreases by as much as 3 eV in either p- or n-type material. P, Li, and Na are shallow donors, but their solubilities are too low for incorporation into diamond through in-diffusion. It is energetically favorable for B and N to dissolve in diamond, which explains their prevalence in natural diamond. The calculations explain for the first time the reasons for the distortion of atoms around N from the fully tetrahedral site, as well as why N is a deep rather than a shallow donor. We also consider the effects of simultaneous doping with N and B on the thermodynamic equilibrium between diamond and graphite.
Quasi-Equilibrium Nucleation and Growth of Diamond and Cubic Boron-Nitride
Authors: Bar-Yam Y. , Lei T. , Moustakas T. D. , Allan D. C. , Teter M. P.
Published: March 2011

Material growth is an inherently non-equilibrium process. However, thermodynamic considerations often provide important insight into material growth, the structure of grown materials, and process control parameters. In essence, thermodynamic considerations are important when activated processes are either slow or fast on the time scale of the growth. Activated kinetic processes are important when their time scale is the same as that of growth. Realistic ab-initio calculations of material structure and dynamics can provide a microscopic understanding of both thermodynamics and the kinetics of material growth. The primary focus of this article is a recently proposed defect-assisted multiple-regrowth stabilization of cubic phases. in this theory the incorporation of vacancies at the growth face changes the relative binding energy of cubic versus hexagonal phases so that diamond and cubic boron nitride can nucleate and grow. This theory predicts that diamond nucleation and growth is enhanced under electron rich or positive ion conditions. Experimental results on growth of both diamond and cubic boron nitride that motivate and support theoretical predictions are described. Cubic boron-nitride grows under off-stoichiometric conditions. The nucleation rate of diamond is increased by many orders of magnitude when a flux of electrons impinges upon the surface. Raman line broadening and ESR measurements indicate the presence of significant concentrations of point defects. Predictions and experimental evidence for both n and p type doping will be discussed. Ab-initio calculations of key kinetic processes and thermodynamic quantities for diamond and boron nitride growth are described.
Interstitial Impurities in Wurtzite Vs. Zincblende Semiconductors: The Case of H In SiC
Authors: Roberson M. A. , Estreicher S. K.
Published: March 2011

Most compound semiconductors crystallize in the zincblende or the wurtzite structures. In both cases, all the host atoms are tetrahedrally coordinated. However, the two lattices have no high symmetry interstitial sites in common. As a result, the stability, lowest-energy configuration, electronic structures, and barriers for diffusion of interstitial impurities are in general very different. This situation is illustrated here in the case of interstitial H in 3C (zincblende) and 2H (wurtzite) SiC. The results can be used to obtain the properties of H in other hexagonal polytypes, in particular 6H-SiC.
Diamond Growth from Sputtered Atomic Carbon and Hydrogen Gas
Authors: Kelly Michael A. , Kapoor Sanjiv , Olson Darin S. , Hagstrom Stig B.
Published: March 2011

Diamond thin films were grown on a scratched silicon crystal surface by a novel CVD technique. The heated substrate, mounted on a rotating platform, was exposed to a bombardment of sputtered carbon atoms, from a graphite target in a helium plasma, and subsequently bombarded by atomic hydrogen generated by a hot tungsten filament. The resulting diamond films were characterized by Raman spectroscopy and SEM. The SEM images indicate highly faceted diamond crystals and the Raman spectra show a single narrow peak characteristic of pure diamond with no graphitic component. The effective growth rate is about 0.5 microns per hour of exposure time. The novel sequential CVD reactor is described and possible growth mechanisms are discussed.