bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Laser Annealing on the Furnace Annealed Amorphous Silicon Thin Films
Authors: Choi Kwon-Young , Jeon Jae-Hong , Han Min-Koo , Kim Yong-Sang
Published: April 2011

The performance of polysilicon thin film transistors fabricated by two-step annealing, which consists of furnace annealing and subsequent excimer laser annealing, is described. It was found that the average grain size of low temperature furnace annealed polysilicon films was several times larger than that of excimer laser annealed polysilicon films while the density of in-grain defect in low temperature furnace annealed films was much higher than that of excimer laser annealed film. The device characteristics of the low temperature furnace annealed polysilicon thin film transistors were improved significantly by postannealing, such as high temperature furnace annealing and excimer laser annealing, due to the effective elimination of in-grain defects. The density of trap states, which was extracted from the transfer curves of polysilicon thin film transistors, was used to demonstrate the effects of modifying the deep and tail trap levels by two-step annealing.
Wide-Gap a-Si:H Fabricated by Controlling Voids
Authors: Yoshino K. , Futako W. , Wasai Y. , Shimizu I.
Published: April 2011

High quality wide gap hydrogenated amorphous silicon has been prepared using the chemical annealing technique. It was possible to prepare materials with band gaps ranging 1.8 to 2.1 eV by varying the preparation parameters. Low defect densities less than (3–8) x 1015 cm-3 could be maintained over the entire band gap range. Improved stability for light soaking was also observed in the wide gap materials.
The Influence of Hydrogen Dilution and Substrate Temperature in Hot-Wire Deposition of Amorphous and Microcrystalline Silicon With Filament Temperatures Between 1900 And 2500 °C
Authors: Conde J. P. , Brogueira P. , Castanha R. , Chu V.
Published: April 2011

The effect of hydrogen dilution and substrate temperature on the optoelectronic and structural properties of thin films deposited by hot-wire chemical vapor deposition with filament temperatures between 1900 and 2500 °C from silane and hydrogen are studied. Amorphous silicon films are obtained at high deposition rates for hydrogen dilutions below 90%. The deposition rate scales approximately linearly with the filament temperature in this regime. Microcrystalline films are obtained for hydrogen dilution above 90%, independently of the filament temperature and substrate temperature, with much lower growth rates. The Raman spectrum of these films shows high crystalline fraction and small grain size. High conductivity films, typical of microcrystalline silicon, with high growth rates were achieved by either increasing the substrate temperature at low hydrogen dilution, or by using a hydrogen dilution just at the amorphous to microcrystalline transition point.
The Electronic Properties of a-Si:H Deposited With Hydrogen or Helium Dilution
Authors: Zhong F. , Hong W. S. , Perez-Mendez V. , Chen C. C. , Cohen J. D.
Published: April 2011

We have applied the Drive-Level Capacitance Profiling (DLCP) method to n-i-p a-Si:H diodes to characterize the mid-gap defect densities in the i layer. Our results show that there are no significant changes in the drive-level densities, Ndl, in n-i-p diodes and p+-i-m as well as n-i-m Schottky diodes, which indicates that DLCP can directly provide reliable energy distribution and spatial distribution of the mid-gap defects in the n-i-p device. We have found that the ratio of Ndl to ND*, the ionized defect density determined by hole onset measurement, is changed with the deposition conditions; it is 3 for standard samples, 2 for helium diluted samples and 6 for hydrogen diluted samples. These results indicate that there may be different defect distributions in these materials, which suggest the ratio of charged (D-) density to the neutral defect (D0) density may be altered when growth conditions are varied.
Mechanical and Electrical properties of Hydrogen or Helium Diluted a-Si:H Prepared at Low Temperatures
Authors: Hong Wan-Shick , Zhong Fan , Perez-Mendez Victor
Published: April 2011

Hydrogen or helium dilution of silane has been used to improve charge transport characteristics or deposition rate for thick amorphous silicon layers. In both cases, mechanical instability, such as peeling-off, due to high strain energy stored in the a-Si:H film is one of the major concerns. Growing the a-Si:H film at temperatures below 150°C brought the residual stress in the film to a level low enough to prevent delamination. The defect density increased at the same time, but it could be recovered by annealing at 160°C for 100 hours without affecting the stress state. In the hydrogen-diluted material, the deposition condition for optimum mobility and defect density values corresponded to the onset of the microcrystalline formation, and this relationship was confirmed by Transmission Electron Microscopy (TEM). Existence of a small amount of an ordered phase in the helium-diluted material, which was hardly observed by the TEM, was revealed by IR absorption spectra and supported by the change in ratio of photo-todark conductivity compared to that of undiluted material.
Study of a-Si:H / c-Si Heterojunctions for PV Applications
Authors: Zignani F. , Galloni R. , Rizzoli R. , Ruth M. , Summonte C. , Pinghini R. , Zini Q. , Rava P. , Madan A. , Tsuo Y. S.
Published: April 2011

a-Si:H / c-Si heterojunction diodes were produced by PECVD with varying amorphous silicon layer thickness and hydrogen dilution of the gas phase. An accurate determination of the growth rate also in the initial stages of the deposition was made possible by an original chemical method based on the dissolution of the films followed by spectroscopical analysis of the obtained solution.

The electrical characterization of the diodes confirms the generation - recombination - multitunneling nature of the transport. Although H2 dilution is important, however, beyond a certain level it is detrimental for the junction quality, probably due to the transition to a microcrystalline phase deposition. Solar cells were also produced, the best results being an open circuit voltage of 610 mV and an intrinsic efficiency of 14.2%.
A Study of Local and Extended Migration of H and Defects in a-Si by Molecular Dynamics Simulations
Authors: Fedders Peter A.
Published: April 2011

We report on extensive molecular dynamics (MD) simulations on a-Si:H for up to 5 Ps using the ab initio code of Sankey and Drabold. The supercells contain about 70 atoms and only one defect in order to minimize defect-defect interaction. Simulations on supercell samples that originally contain one bond centered (BC) H in an otherwise defect free sample exhibit BC to BC diffusion as in c-Si. However, we also observe localized motion of defects and H atoms on a very fast time scale that probably has been observed in several experiments.
Defect Formation During Deposition of Undoped a-Si:H BY PE-CVD
Authors: Maeda Keiji , Umezu Ikurou
Published: April 2011

Dependence of the as-grown defect concentration in PECVD undoped a-Si:H on the deposition parameters, i.e., substrate temperature and precursor density in the plasma produced by H2 dilution of SiH4 gas, is investigated. It is found that the defect density behaves similarly to the concentration of SiH2 configuration in the films deposited at substrate temperatures below 300 °C. The defect concentration, however, varies proportionally to about the 3rd to 4th power of the SiH2 concentration depending on the deposition condition. Based on the surface reaction mechanism proposed in our previous paper, a large enthalpy change is expected to accompany the bimolecular reaction of the adsorbed SiH3 radicals, which incorporates the SiH2 configuration into the network. Characteristics of the defect formation caused by tile breaking Si-Si bond near the growing surface owing to this energy is compared with those of the Staebler-Wronski effect. Both similarity in dependence on II atom concentration and difference in annealing temperature are discussed. It is concluded that the as-grown defects are most likely formed during deposition owing to the large enthalpy change accompanying the bimolecular surface reaction.
Photoluminescence in Hydrogenated Amorphous Silicon with Sulfur
Authors: Chen S. , Taylor P. C. , Wang S. L. , Viner J. M.
Published: April 2011

Photoluminescence (PL) has been measured at 80 K in a series of samples of sulfur doped a- Si:H using above- and below-bandgap excitation energies (2.4 and 1.38 eV). In addition, the absorption coefficients at room temperature have been obtained using photothermal deflection spectroscopy (PDS). At light sulfur doping levels (S/Si < 10-2), the Urbach slopes of the absorption coefficients on a semilog plot and the optical energy gaps, as measured by the points at which ca =104 cm-1, are independent of sulfur concentration. The slopes decrease and optical gaps increase with increasing doping level for doping levels above 10-2. At light sulfur doping levels the PL spectra excited with both above- and below-gap light are independent of sulfur concentration. For larger sulfur concentrations the shapes of the PL spectra vary. In particular, for S/Si > 10-2the peak of the PL spectrum shifts to below 0.8 eV using below-gap excitation at 1.38 eV, and the defect PL band dominates. Comparing the PL spectra of sulfur- and phosphorus-doped samples, the PL spectra change for sulfur doping above 10-2 and for phosphorus doping above 1 ppm. This trend is consistent with inefficient sulfur doping.
Subtleties of Capacitance Transients in Amorphous Silicon
Authors: Crandall Richard S. , Lips Klaus
Published: April 2011

Using junction capacitance methods, we describe the effect of contacts on charge emission transients in n-type hydrogenated amorphous silicon. The results demonstrate some of the difficulties encountered in observing and interpreting anomalous temperature independent emission transients(“slow relaxation”).
Interdiffusion and Carrier Recombination in High Intensity Transient Gratings
Authors: Schwarz R. , Grebner S. , Nebel C. E. , Lanz M. , Stutzmann M.
Published: April 2011

Transient grating (TG) experiments were performed to study carrier diffusion and recombination in amorphous silicon films (a-Si:H) at high light intensities using 8 ns pulses from a frequency-doubled Nd:YAG laser. The ambipolar diffusion coefficients reached about 10−2cm2/s, which is 2 orders of magnitude larger than the steady-state value. Similar results were obtained in intrinsic, p-, and n-doped a-Si:H films, indicating that the diffusion coefficients in all cases reflect the near band edge mobility of the slower carriers, that is holes. In particular, the p-type sample shows an initially fast, then a slow grating efficiency decay, consistent with dispersive transport.
Quantum Confinement in Single Layer a-Si:H Films
Authors: Koehler S. A. , Fritzsche H.
Published: April 2011

Quantum confinement effects in the transmission spectrum of thin amorphous silicon, a-Si:H, films require a coherence length comparable to the film thickness, as well as good film homogeneity. After a careful investigation, we conclude that there is no quantum confinement in single layer a-Si:H films at room temperature.
Improvement of the ITO-P Interface in a-Si:H Solar Cells Using a Thin SiO Intermediate Layer
Authors: Nunes de carvalho C. , De Nijs J. M. M. , Ferreira I. , Fortunato E. , Martins R.
Published: April 2011

The use of ITO thin films on glass/ITO/p-i-n/metal amorphous silicon solar cells is reviewed. It is suggested a new application for silicon monoxide thin films on the ITO-p interface, as an intermediate layer, to minimize the ITO thin film deterioration process, during the early stage of exposure to a silane plasma rich in hydrogen. The thickness of the silicon monoxide thin films is chosen not to worsen the optical and electrical properties of the ITO thin films. The ITO-p interface is optimized (due to impurities diffusion decrease), leading to an overall improvement of the device performance
Nano-Scale Resolved Detection of Photo-Current in a-Si:H Films
Authors: Koida Takashi , Kawasaki Masashi , Maruyama Ryuichiro , Matsuse Mitsutaka , Koinuma Hideomi
Published: April 2011

The growth mode of a-Si:H plasma CVD film was observed by AFM to range from homogeneous deposition to heterogeneous island formation depending on the substrate material and deposition temperature. The correlation between the grain-like structure and electric property of the film deposited on transparent conductive SnO2, substrates has been elucidated by using an AFM with a conductive cantilever. The local distribution of photo-current in the a-Si:H films was found to agree well with the topographic image; the photo-current around the grain boundaries was lower than that on the grains. The effect of surface treatment with an aqueous HF solution indicates that the imhomogeneity in the photo-current originates from the preferential oxidation around the grain boundaries rather than intrinsic electric property.
A Novel Device Structure for High Voltage, High Performance Amorphous Silicon Thin-Film Transistors
Authors: Miri A. M. , Gudem P. S. , Chamberlain S. G. , Nathan A.
Published: April 2011

Conventional high voltage thin-film transistors (HVTFTs) suffer from performance limitations such as low on-current, Vx. shift and large curvature in the linear region of the output characteristics. These limitations are associated with the highly resistive dead region in conventional HVTFT structures. In this paper, we present a novel TFT structure which has a high on-current, improved output characteristics in the linear region, and no Vx, shift. The higher on-current and significant improvement in output characteristics allows faster switching. Elimination of the Vx shift leads to more reliable circuit operation. The new structure is based on the conventional low voltage TFT (LVTFT) structure except that it does not suffer from low-voltage breakdown. The low-voltage breakdown of the gate nitride in conventional LVTFTs is perceived to be due to spiking of the drain metallization into the underlying layers which creates regions of very high electric field. In our novel structure, a higher breakdown is achieved by locating the metal contacts away from the gate edge while keeping the necessary drain to gate overlap through a heavily doped microcrystalline layer. Therefore, the new TFT extends the same performance as LVTFTs to high voltage operation. Furthermore, this structure also enhances the yield and reliability by minimizing the common faults in TFTs such as short circuits between gate, source and drain.
On the Investigation of Power and Reliability Performance of Pseudomorphic AlGaAs/InGaAs HEMT's
Authors: Li G.P. , Chou Y.C. , Chen Y.C. , Wu C.S. , Yu K.K. , Midford T.A. , Liu Y. , Sonek G.J. , Wei X. , Tromberg B.J.
Published: April 2011

In this work, power and reliability performance of pseudomorphic AIGaAs/InGaAs HEMT's are investigated by 2-D device simulation, spatially-resolved electro-luminescence, light emission spectra analysis, and gate current instabilities. A two-dimensional device simulation was used to exploit the off/on state breakdown origins in the power PHEMT's and to explore the physical mechanisms responsible for light emission in both conditions. A correlation between simulated results and light emission spectra highlights the breakdown origins in PHEMT's.

PHEMT's subjected to off-state breakdown stress and on-state hot carrier stress show changes in device characteristics. While gate leakage current, i.e. a surface leakage component associated with the surface passivation layer is reduced by these stresses, a reduction in drain current, transconductance degradation, and an increase in the impact ionization generated gate current are also observed.

Further improvement in off/on state breakdown voltages and device reliability calls for device structure optimization for lower electric field design, surface passivation treatment for lower surface leakage current, and Schottky barrier enhancement for lower gate current.
Selective-Area Epitaxy and In-Situ Etching of Gaas Using Tris- Dimethylaminoarsenic By Chemical Beam Epitaxy
Authors: Li N. Y. , Tu C. W.
Published: April 2011

In this study, we shall first report selective-area epitaxy (SAE) of GaAs by chemical beam epitaxy (CBE) using tris-dimethylaminoarsenic (TDMAAs), a safer alternative source to arsine (AsH3), as the group V source. With triethylgallium (TEGa) and TDMAAs, true selectivity of GaAs can be achieved at a growth temperature of 470°C, which is much lower than the 600°C in the case of using TEGa and arsenic (As4) or AsH3. Secondly, we apply SAE of carbon-doped AIGaAs/GaAs to a heterojunction bipolar transistor (HBT) with a regrown external base, which exhibits a better device performance. Finally, the etching effect and the etched/regrown interface of GaAs using TDMAAs will be discussed.
Cleaved Facets in Gan by Wafer Fusion of Gan to Inp
Authors: Sink R. K. , Keller S. , Keller B. P. , Babić D. I. , HOLMES A. L. , Kapolnek D. , Wu X. H. , Speck J. S. , Denbaars S. P. , Bowers J. E.
Published: April 2011

Basal plane sapphire is a common substrate for the heteroepitaxy of GaN. This presents a challenge for fabrication of cleaved facet GaN lasers because the natural cleavage planes in (0001) α-A12O3 are not perpendicular to the wafer surface. This paper describes a method for achieving perpendicular cleaved facets through wafer fusion that can potentially be used to fabricate GaN based in-plane lasers. We demonstrate successful fusion of GaN to InP without voids or oxide at the interface and fabricate optically flat cleaved GaN facets that are parallel to the crystallographic planes of the host InP. I-V measurements have been performed across the n-N fused interface. These results show that the fused interface exhibits a barrier for electrons passing from the InP to the GaN and ohmic conduction of electrons moving in the opposite direction.
Interactions at Metaijinp Interfaces Formed at 300K and 77K
Authors: Palmer J.W. , Anderson W.A. , Hoelzer D.T. , Hardtdegen H.
Published: April 2011

Depositing Pd or Au on n-InP at cryogenic substrate temperatures has previously been found to significantly increase the barrier height of the resulting Schottky diode. Cross-sectional transmission electron microscopy (XTEM) has been performed on Pd/InP and Au/InP interfaces formed at room temperature (RT) and low temperature (LT) to determine the differences responsible for the change in barrier height. In the Pd case, a solid state amorphization which occurs at the interface upon RT metal deposition is nearly eliminated in as-deposited LT Pd/InP diodes. In the Au case, RT deposition results in the initial monolayers of Au entering the InP lattice, while no such effect was observed in the LT Au/InP diodes. It is clear that the LT deposition dramatically reduces the interaction between the metal and substrate, resulting in a greater barrier height. Enhanced barrier height Schottky diodes are crucial to the development of optical and electronic devices on InP. Preliminary results will be discussed on metalsemiconductor- metal (MSM) photodetectors and metal-semiconductor field-effect-transistors (MESFET's) fabricated using the LT process.
A Study of Annealing Behavior of EL2 and EL6 Groups in SI-GaAs
Authors: Fengmei Wu , Zhouying Zhao
Published: April 2011

We present annealing behavior for EL2 and EL6 groups as dominant deep levels in semiinsulating GaAs using Photo Induced Transient Spectroscopy (PITS) measurement. During rapid thermal annealing, a relation has been identified between EL2 group at 0.79 and 0.82 eV and EL6 group at 0.24, 0.27 and 0.82 eV below the conduction band. It is found that they may be close in structure, and belong to the EL2 and EL6 groups, respectively. In rapidly annealed samples, the quantity of all defects in the EL2 group increases, while that in the EL6 group decreases. However, by furnace annealing at 950°C for 5 hours, some of the defects in the EL2 group break up, and the quantity of all defects in the EL6 group increases. It is suggested that the EL2 group and EL6 group are related in their microscopy structures. We then discuss a relation between the two groups and their origins.
The Electric Field Measuring by Phase Selective Photoreflectance
Authors: Hwang J. S. , Chou W. Y. , Tyan S. L. , Wang Y. C. , Shen H.
Published: April 2011

The built-in electric fields in a MBE grown δ-doped GaAs homojunction have been investigated by the techniques of photoreflectance and phase suppression. Two Franz-Keldysh oscillation features originating from two different fields in the structure superimpose with each other in the photoreflectance spectrum. By properly selecting the reference phase of the lock-in amplifier, one of the features can be suppressed, thus enabling us to determine the electric fields from two different regions. We have demonstrated that only two PR spectra, in-phase and outphase components, are needed to find the phase angle which suppresses one of the features. The electric field in the top layer is 3.5 ± 0.2 × 105 V/cm, which is in good agreement with theoretical calculation. The electric field in the buffer layer is 1.2 ± 0.1 × 104 V/cm, which suggests the existence of interface states at the buffer/substrate interface.
Passivation of Carbon Doping in InGaAs During ECR-CVD of SiNx
Authors: Ren F. , Hamm R. A. , Wilson R. G. , Pearton S. J. , Lothian J. R.
Published: April 2011

InGaAs (C) grown by gas-source MBE is found to contain significant concentrations 5 × 1018 cm−3 of hydrogen that is incorporated from the source gases. Subsequent deposition of ECR-CVD SiNx films as surface encapsulation produces additional hydrogen incorporation from the SiD4/N2 precursors, but actually reactivates C acceptors that were passivated in the asgrown InGaAs. Further thermal treatments produce substantial hydrogen in-diffusion from the SiNx film into the InGaAs, causing changes in sheet resistance and contact resistance. These processes simulate several steps in the formation of the base mesa of an InGaAs-based heterojunction bipolar transistor, and show how subtle changes in the temperature of these processes can affect subsequently device performance and apparent reliability.
Polarization Control of Vertical-Cavity Surfaceemitting Lasers by Tilted-Etching of Cavity
Authors: Chu Hye Yong , Yoo Byueng-Su , Park Min Soo , Park Hyo-Hoon
Published: April 2011

We performed a polarization control method for vertical-cavity surface-emitting lasers by tilted-etching of the air-post. Circular laser posts were etched by tilting the substrate toward [110] or [110] direction with an angle of 15° ˜ 20° using reactive ion beam etching. For the laser devices with a diameter of 7 ˜ 10 μm, we observed outstanding selectivity of the polarization state. We found a dominant polarization perpendicular to the tilted direction. The maximum orthogonal polarization suppression ratio was about 25 dB. The selectivity of polarization in the tilted laser post devices is interpreted to be originated from the difference of optical losses of the two waves polarized to the [110] and [110] directions.
Properties of H, O and C in GaN
Authors: Pearton S. J. , Abernathy C. R. , Lee J. W. , Vartuli C. B. , MacKenzie J. D. , Ren F. , Wilson R. G. , Zavada J. M. , Shul R. J. , Zolper J. C.
Published: April 2011

The electrical properties of the light ion impurities H, O and C in GaN have been examined in both as-grown and implanted material. H is found to efficiently passivate acceptors such as Mg, Ca and C. Reactivation occurs at ≥450°C and is enhanced by minority carrier injection. The hydrogen does not leave the GaN crystal until >800°C, and its diffusivity is relatively high (˜10−11cm2/s) even at low temperatures (<200°C) during injection by wet etching, boiling in water or plasma exposure. Oxygen shows a low donor activation efficiency when implanted into GaN, with an ionization level of 30 - 40 meV. It is essentially immobile up to 1100°C. Carbon can produce low p-type levels (3×1017cm−3) in GaN during MOMBE, although there is some evidence it may also create n-type conduction in other nitrides.
Long Wavelength Shifting and Broadening of Quantum Well Infrared Photodetector Response Via Rapid Thermal Annealing
Authors: Sengupta D.K. , Fang W. , Malin J.I. , Kuo H.C. , Horton T. , Curtis A. , Gardner N.F. , Flachsbart B. , Wohlmuth W. , Turnbull D. , Chuang S.L. , Hsieh K. C. , Cheng K.Y. , Adesida I. , Feng M. , Bishop S.G. , Stillman G. E.
Published: April 2011

A shift in the peak response wavelength and a broadening of the photoresponse spectrum is demonstrated for intersubband absorption in n-doped GaAs/AIGaAs multiple quantum well detectors following intermixing of the well and barrier layers during rapid thermal annealing. In general, a decrease in performance is observed for the RTA QWIPs when compared to the as-grown detectors. The peak absolute response of the annealed QWIPs is lower by almost a factor of four, which results in corresponding decrease in quantum efficiency. In addition, the noise performance results in a detectivity which is five times lower than that of QWIPs fabricated from as-grown structures.
Temperature Dependence of the Optical Absorption Edge in Indium Phosphide
Authors: Beaudoin M. , Johnson S.R. , Devries A.J.G. , Mohades-Kassai A. , Tiedje T.
Published: April 2011

Optical bandgap thermometry is a new method for measuring the temperature of semiconductor substrates. In this method, the temperature of the substrate is inferred from the wavelength of the onset of transparency of the substrate which is a measure of its bandgap. Common configurations of this technique are diffuse reflectance and transmittance. In order to calibrate these spectra to substrate temperature and to better understand the temperature dependence of the absorption edge, the transmittance spectra of semi-insulating InP:Fe and n-type InP:S substrates have been measured as a function of temperature in a tube. The width of the absorption edge (Urbach parameter) is found to increase linearly with temperature from 8.7 meV at room temperature to 15.7 meV at 595°C for semi-insulating InP:Fe while it remains independent of temperature at a value of about 21.5 meV for heavily doped (6.5×1018 cm−3) InP:S. For InP:Fe, the temperature dependent part of the width is smaller than predicted by the standard theory where the width of the edge is proportional to the phonon population. The values of the Urbach parameter for InP:Fe are higher than those of semi-insulating GaAs which is attributed to the higher ionicity of InP.
Tem Structural Characterization of Nm-Scale Islands in Highly Mismatched Systems
Authors: Ruvimov S. , Liliental-Weber Z. , Ledentsov N.N. , Grundmann M. , Bimberg D. , Ustinov V.M. , Egorov A.YU. , Kop'ev P.S. , Alferov Zh.I. , Scheerschmidt K. , Gösele U.
Published: April 2011

Transmission electron microscopy has been applied to study the ordering in size and shape of InAs quantum dots and in their lateral distribution. InAs islands were grown by MBE on GaAs substrates at different As-pressures and growth temperatures. Experiments with growth interupption support the theoretical predictions concerning equilibrium island size, shape and arrangement. The stability of the equilibrium dot arrays to changing of growth conditions was studied by varying the deposition temperature, arsenic pressure or growth interruption time. Significant deviation from the optimal As-pressure towards both the lower and higher values was shown to supress the formation of InAs dots resulting either in mesoscopic InAs clusters or 2D corrugated islands. Energy benefit due to the strain relaxation at island edges explains the experimental results better than kinetic consideration.
Theoretical Study of InAsSb/InTlSB Superlattice for the Far Infrared Detector
Authors: Iyer S. , Chowdhury-Nagle S. , Li J. , Bajaj K.K.
Published: April 2011

We propose a novel superlattice (SL) InAsySb1−y)/InxTl1−xSb lattice matched to InSb for a potential application as an infrared detector material in the 8–12 μm wavelength range. We report on the results of energy band calculations for this SL using the modified Kronig-Penney model. Our preliminary calculations indicate that InAs0.07Sb0.93/In0.93Tl0.07Sb would exhibit a type-I SL with conduction band offset of 34 meV and valence band offset of 53 meV at 0K. Due to the lack of accurate information on material parameters, namely, energy offsets and effective masses of InTlSb, these were estimated by comparison with the behavior of HgCdTe system. The theory predicts three heavy hole subbands and one partially confined electron in the 30Å InAs0.07Sb0.93/100Å In0.93Tl0.07Sb SL. The band gap of the SL was computed to be 0.127 eV (9.7 μm). It is expected that this SL will allow improvements in the InTlSb epilayers’ structural quality as it will be sandwiched between higher quality zincblende InAsSb layers.
Surface Passivation of Gaas-Based Phemt by Hydrogen Ion Irradiation
Authors: Shi Song S. , Chang Ying-Lan , Hu Evelyn L. , Brown Julia J.
Published: April 2011

Surface passivation is a key issue in compound semiconductor device technology. The high density of surface states on unpassivated surfaces can lead to excessive non-radiative recombination at the surface, affecting optical devices, or provide leakage and low-field breakdown in electronic devices. Our previous studies on low energy, low-dose hydrogen ion treatment carried out at room temperature showed long-term improvement in the optical properties of near surface quantum wells. We have accordingly applied this process to GaAs-based pseudomorphic HEMTs (PHEMT) in order to improve their power performance. Although our process is designed so that the hydrogen reactions are confined to the surface of the substrate, a critical factor in the success of this treatment is the extent of in-diffusion of the hydrogen, and the possibility of dopant passivation. PHEMT structures were hydrogenated at various conditions and both Hall mobility and carrier density were monitored. For a low hydrogen ion dose (3 × 1016 cm−2) at 80 eV energy, some degradation of Hall mobility and carrier density was noted after the treatment, but full recovery of both parameters was achieved after a 400°C thermal anneal. Much higher hydrogen doses resulted in severe degradation of mobility and carrier density, which were only partially recovered after thermal anneal. Measurements on actual PHEMT devices showed an approximately 15% decrease in the transconductance, and in addition, a 60% decrease in the gate-to-drain leakage current after irradiation with 80 eV hydrogen ions at a dose of 3 × 1016 cm−2. The decrease of the leakage current indicates that passivation is taking place. The decrease of the transconductance suggests that hydrogen may be diffusing into the regions of the dopants. Optimization of the hydrogenation parameters should allow leakage reduction without sacrifice of transconductance.
Surface Stabilization Of Inp Using Cds Thin Films
Authors: Davis A. , Dauplaise H.M. , Vaccaro K. , Demczyk B.G. , Ramseyer G.O. , Lorenzo J.P.
Published: April 2011

A chemical bath deposition process was used to grow thin (25–200 Å) films of cadmium sulfide on (100) InP from an aqueous solution of ammonium hydroxide, cadmium sulfate, and thiourea at 75–85 °C. Reflection high energy electron diffraction (RHEED) and transmission electron microscopy (TEM) show that ˜30 Å films are amorphous, while thicker films exhibit a cubic polycrystalline microstructure, with a preferred orientation in the [110] direction. X-ray photoelectron spectroscopy (XPS) shows the CdS treatment both removes the native oxides of InP and forms a stabilizing layer which protects the substrate from re-oxidation. Quasistatic capacitance-voltage response of MIS capacitors on InP, with a CdS layer between the insulator and substrate, exhibits well defined regions of accumulation, depletion, and inversion, indicating a high-quality interface region. An experimental Cmin/Cox, value of 0.28 was obtained, compared to the theoretical value of 0.07. The density of interface states (Dit) was reduced from 1012 to 1011 eV−1cm−2 after CdS treatment when calculated by the high-low method. InP MISFETs fabricated using CdS interlayers showed greatly enhanced device performance over untreated MISFETs.
Luminescence Quenching in Erbium-Doped Hydrogenated Amorphous Silicon
Authors: Polman A. , Shin Jung H. , Serna R. , Hovenb G. N. Van Den , van Sark W. G. J. H. M. , Vredenberg A. M. , Lombardo S. , Campisano S. U.
Published: April 2011

Hydrogenated amorphous silicon thin films, co-doped with oxygen, are made using lowpressure chemical vapor deposition (LPCVD) or plasma-enhanced chemical vapor deposition (PECVD). The films are implanted with Er to a peak concentration of 0.2 at.%. Roomtemperature photoluminescence at 1.54 μm is observed in both amorphous materials, after thermal annealing at 300–400 °C. The PECVD films with low 0 content (0.3, 1.3 at.%) show a luminescence intensity quenching by a factor 7–15 as the temperature is raised from 10 K to room temperature. The quenching is well correlated with a decrease in luminescence lifetime, indicating that non-radiative decay of excited Er3+ is the dominant quenching mechanism as the temperature is increased. In the LPCVD films, with 31 at.% 0, the quenching is only a factor 3, and no lifetime quenching is observed. The results are interpreted in the context of an impurity Auger excitation model, taking into account the fact that oxygen modifies the Si bandgap and the Er-related defect levels in the gap.
On the Excitation Mechanism of Erbium and Ytterbium in the Quaternary Compounds InGaAsP
Authors: Wellmann Peter , Winnacker Albrecht , Pensl Gerhard
Published: April 2011

An efficient transfer of excitonic energy to rare earth (RE) ions is crucial for possible optoelectronic applications of RE doped semiconductors. In order to investigate the energy transfer mechanism to RE ions after optical above bandgap excitation we studied the intensity of the 4I13/2 →4 4I15/2-transition of Er3+ (1.54μm) and the one of the 2F5/2 →2F7/2 -transition of Yb3+ (lμm) (loped into InGaAsP-layers lattice matched to InP. By varying the composition of the quaternary compoun ds, the bandgap energy together with the RE bound exciton energy were tuned relative to the RE excitation energy, and the effect on the RE luminescence intensity was observed. The results can be interpreted by stating a) that the energy transfer to the RE proceeds via the RE bound exciton, and b) that the intensity of the RE luminescence is essentially determined by the rate of back transfer of the RE excitation energy ERE to the bound exciton (with excitation energy Ebe). In this back transfer the energy of the excited RE ion plus the energy of 0, 1, 2 ... L0-phonons (energy Elo) is used to reexcite the bound exciton, instead of being emitted as an RE luminescence photon. For compositions where Ebe = ERE + n. Elo (n = 0, 1, 2...) we have a maximum of back transfer and correspondingly a, minimum in RE luminescence. In between the intensity has a, maximum.
Excitation Mechanisms and Light Emitting Device Performances in Er-Doped Crystalline Si
Authors: Priolo F. , Coffa S. , Franzo G. , Polman A.
Published: April 2011

In this paper the performances of room temperature operating light emitting diodes (LEDs), fabricated by Er ion implantation of crystalline silicon, are investigated in detail. It is shown that 1.54 μm emission is observed under both forward and reverse bias operation, with a much higher intensity under reverse bias. The excitation mechanisms of Er3+ are demonstrated to be very different in the two cases: under forward bias Er is excited through the electron - hole recombination at an Er - related level, while under reverse bias impact excitation by hot carriers represents the excitation process. This last mechanism is shown to occur with a cross section of 6 × 10−17 cm2 and population inversion of the excitable Er sites within the depletion region is demonstrated. The efficiency and limitations of this approach are also discussed.
Properties and Growth of MBE Grown Erbium Doped Gallium Arsenide Co-Doped with Selenium
Authors: Rutter P. , Singer K. E. , Peaker A. R. , Wright A. C.
Published: April 2011

The growth of erbium doped GaAs by molecular beam epitaxy (MBE) can, depending on growth conditions, result in the precipitation of small spherical particles of erbium arsenide. It has been observed that by reducing the V:III (As:Ga) flux ratio to close to stoichiometry wirelike precipitates roughly aligned in the direction of growth are produced. The concentration of erbium incorporated into the GaAs lattice for a constant erbium flux is also affected by the As:Ga flux ratio with an increase in erbium doping being observed with decreasing As:Ga flux ratio.

Electrical measurements have been performed on erbium doped GaAs samples co-doped with selenium, an n-type dopant. Measurements have revealed that when erbium is present, the electron concentration is reduced by an amount approximately equal to 70% of the erbium concentration. DLTS measurements have shown that although large concentrations of deep levels are present in erbium doped material, the measured concentration of these deep levels is not high enough to account for the observed reduction in electron concentration with erbium doping.
Properties of Ion Implanted and UHV-CVD Grown Si:Er
Authors: Morse M. , Zheng B. , Palm J. , Duan X. , Kimerling L. C.
Published: April 2011

We have fabricated Si:Er films by ion implantation and ultra-high vacuum chemical vapor deposition (UHV-CVD). The energy of the ion implantation was varied from 200 keV to 4.5 MeV. Oxygen was co-implanted to overlap the erbium profile. At implant energies of 400 keV, we found that the luminescence was optimized at a lower annealing temperature (800° C, 30 minutes) than that needed for the 4.5 MeV implant (900°C, 30 minutes). The light intensity per erbium atom is critically dependent on the implantation energy. However, spreading resistance measurements show that the donor activity of the implanted erbium is independent of energy. We have correlated the donor activity with quantum efficiency by varying the donor spatial distribution and concentration through post implantation heat treatments.

For the UHV-CVD grown Si:Er films, two erbium metallorganic precursors, Er(TMHD)3 and Er(FOD)3. have been used for growths from 550–620°C. The thickness of the erbium layers are similar to that of implanted devices but the Er concentration of 4 × 1021/cm3 exceeded the implanted material by two orders of magnitude.
Low-Temperature Growth of Si:Er by Electron Cyclotron Resonance Pecvd Using Metal Organics
Authors: Andry P. S. , Varhue W. J. , Adams E. , Lavoie M. , Klein P. B. , Hengehold R. , Hunter J.
Published: April 2011

Epitaxial growth of Er-doped silicon films has been performed by plasma-enhanced chemical vapor deposition at low temperature (430°C) using an electron cyclotron resonance source. The goal was to incorporate an optically active center, erbium surrounded by nitrogen, through the use of the metal organic compound tris (bis trimethyl silyl amido) erbium. Films were analyzed by Rutherford backscatter spectrometry, secondary ion mass spectroscopy and high resolution x-ray diffraction. The characteristic 1.54 μm emission was observed by photoluminescence spectroscopy. Previous attempts to incorporate the complex (ErO6) using tris (2,2,6,6-tetramethyl-3,5-heptanedionato) erbium (III) indicated that excessive interstitial carbon lowered epitaxial quality and reduced photoluminescent intensity. In this study, much of the carbon was introduced onto substitutional sites maintaining good epitaxial growth. A response surface method was employed to find the plasma growth parameters yielding the highest quality luminescent films. Luminescent intensity increased for anneals up to 600°C but decreased at higher temperatures.
Neodymium and Erbium Implanted Gan
Authors: Silkowski E. , Yeo Y. K. , Hengehold R. L. , Goldenberg B. , Pomrenke G. S.
Published: April 2011

Strong rare earth (RE) emissions from Nd and Er implanted into MOCVD grown GaN were observed through photoluminescence (PL) with below bandgap excitation from an Ar+laser. Three well resolved manifolds of 4f lines from the crystal-field split 4F3/2 → 4I9/2, 4F3/2 → 4I11/2, and 4F3/2 → 4I13/2 transitions of Nd3+ were observed at low temperature at ˜0.98, ˜1.14, and ˜1.46 μm, respectively. The Er implanted GaN showed both the 4I13/2 → 4I15/2 Er3+ transition at ˜1.54 μm and the 4I11/2 → 4I15/2 Er3+ transition at ˜1.00 μm. The Er luminescence at ˜1.54 μm and Nd luminescence at ˜1.1 μm persisted to room temperature. Both Er and Nd implanted samples showed increasing RE3+ signal as annealing temperature increased from 700 to 1000 °C. The growth of new 4f crystal-field split-lines in the ˜1.54 μm 4I13/2 → 4I15/2 manifold as annealing temperature was increased to 1000 °C suggests multiple Er3+ radiative centers.
Incorporation of High Concentration Luminescent Er Centers in Si and Porous Si by Electroplating
Authors: Sheng Chi , Cai Yongming , Gong Dawei , Huang Darning , Liu Xiaohan , Wang Xun
Published: April 2011

It is found that Er could only be deposited on a Si cathode by electrolysis of near neutral ErCl3 electrolyte with a large current density. The deposited Er hydrolytic layer reacts with Si at 1200 °C to form the activated Er centers that emit a 1.533 μm photoluminescence peak at room temperature. By applying this process to porous Si, an apparent doping concentration of Er larger than 1019/cm3 in the whole porous Si layer and a strong PL intensity with little temperature quenching are achieved.
High Electric Field Breakdown of 4H-SiC PN Junction Diodes
Authors: Tin C. C. , Madangarli V. , Hu R. , Luckowski E. , Casady J. , Isaacs-Smith T. , Gradinaru G. , Sudarshan T. S. , Johnson R. W.
Published: April 2011

We have characterized the high electric field breakdown process of several epitaxial 4H-SiC p-n structures with oxide passivation. The breakdown voltage was found to be dependent on the size of the diode structures as well as their proximity to any structural defects. The time dependence of the breakdown process was also measured to determine the characteristics of the breakdown mechanism. This time dependence measurement provides an indication of the quality of the diode structures. Both soft and abrupt breakdown mechanisms were observed showing the influence of defects on the high field behavior of the diode structures. Measurements done with and without the use of Fluorinert fluid did not show any difference in the breakdown voltage indicating that surface flashover breakdown mechanism did not play a major role in the avalanche breakdown process.
Optimization of Reactor Geometry and Growth Conditions for GaN Halide Vapor Phase Epitaxy
Authors: Safvi S. A. , Perkins N. R. , Horton M. N. , Thon A. , Zhi D. , Kuech T. F.
Published: April 2011

A numerical model of an experimental gallium nitride horizontal vapor phase epitaxy reactor is presented. The model predicts the flow, concentration profiles, and growth rates. The effects of flowrate variation and geometry on the growth rate, growth uniformity and crystal quality were investigated. Numerical model predictions are compared to experimentally observed values. Parasitic gas phase reactions between group III and group V sources and deposition of material on the wall are shown to lead to reduced overall growth rates and inferior crystal quality. A low ammonia concentration is correlated to deposition of polycrystalline films. An optimum HVPE growth process requires selection of reactor geometry and operating conditions to minimize parasitic reactions and wall deposition while providing a uniform reactant distribution across the substrate.
Structural Characterization of Thick Gan Films Grown by Hydride Vapor Phase Epitaxy
Authors: Romano L. T. , Molnar R. J. , Krusor B. S. , Anderson G. A. , Bour D. P. , Maki P.
Published: April 2011

The structural quality of GaN films grown by hydride vapor phase epitaxy (HVPE) was characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD), and atomic force microscopy (AFM). Films were grown up to 40μm on sapphire with either a GaC1 pretreatment prior to growth or on a ZnO buffer layer. Dislocation densities were found to decrease with increasing film thickness. This is attributed to the mixed nature of the defects present in the film which enabled dislocation annihilation. The thickest film had a defect density of 5×107 dislocations/cm2.
Nucleation and Growth of Oriented Diamond Films on Nickel Substrates
Authors: Yang P. C. , Liu W. , Tucker D. A. , Wolden C. A. , Davis R. F. , Glass J. T. , Prater J. T. , Sitar. Z.
Published: April 2011

(100) and (111) oriented diamond films were grown on similarly oriented single crystal Ni substrates using a multi-step seeding and growth process.In-situreflection monitoring revealed large surface reflectivity changes upon heating of the seeded substrate in H2. The reflectivity change was attributed to the surface melting and dissolution of the seeding particles. The presence of atomic hydrogen lowered the eutectic melting point of the Ni-C compound from 1325°C to about 1100°C. It appeared that the molten Ni-C-H surface layer suppressed graphite formation, which is normally observed in diamond growth on Ni, and promoted diamond nucleation. The oriented diamond films were also obtained using non-diamond carbon seeding. Based on experimental observation, a proposed model is described to explain the nucleation mechanism from the molten Ni-C-H surface layer.
Nucleation and Growth of Gallium Nitride Films on Si and Sapphire Substrates Using Buffer Layers
Authors: Perkins N. R. , Horton M. N. , Zhi D. , Matyi R. J. , Bandic Z. Z. , McGill T. C. , Kuecht T. F.
Published: April 2011

We have investigated the nucleation and growth of gallium nitride (GaN) films on silicon and sapphire substrates using halide vapor phase epitaxy (HVPE). GaN growth was carried out on bare Si and sapphire surfaces, as well as on MOVPE-grown GaN buffer layers. HVPE growth on MOVPE GaN/AlN buffer layers results in lower defect densities as determined by x-ray than growth directly on sapphire. HVPE GaN films grown directly on sapphire exhibit strong near-edge photoluminescence, a pronounced lack of deep level-based luminescence, and x-ray FWHM values of 16 arcsec by an x-ray θ-2θ scan. The crystallinity of GaN films on sapphire is dominated by the presence of rotational misorientation domains, as measured by xray ω-scan diffractometry, which tend to decrease with increasing thickness or with the use of a homoepitaxial MOVPE buffer layer. The effect of increasing film thickness on the defect density of the epilayer was studied. In contrast, the HVPE growth of nitride films directly on silicon is complicated by mechanisms involving the formation of silicon nitrides and oxides at the initial growth front.
Properties of Tetrahedral Amorphous Carbon Deposited by A Filtered Cathodic Vacuum ARC
Authors: Chhowalla M , Chen C W , Kleinsorge B , Robertson J , Amaratunga G A J , Milne W I
Published: April 2011

The properties of a highly sp3 bonded form of amorphous carbon denoted ta-C deposited from a filtered cathodic vacuum arc (FCVA) are described as a function of ion energy and deposition temperature. The sp3 fraction depends strongly on ion energy and reaches 85% at an ion energy of 100 eV. Other properties such as density and band gap vary in a similar fashion, with the optical gap reaching a maximum of 2.3 eV. These films are very smooth with area roughness of order 1 nm. The sp3 fraction falls suddenly to almost zero for deposition above about 200°C.