bluuebunny/crossref_metadata_2025 huggingface dataset:
The Potential of Hydrogenated Amorphous Silicon-Sulfur Alloys for Absorber Materials in Photovoltaic Devices
Authors: Taylor P. C. , Wang S. L.
Published: April 2011

The group VI element, sulfur, is an inefficient donor in hydrogenated amorphous silicon (a-Si:H). The compensation by sulfur donors of the p-type conductivity obtained with diborane in a-Si:H provides additional evidence of the role of sulfur as a donor. By adding equal amounts of diborane and hydrogen sulfide in the plasma the dark conductivity at room temperature can be reduced by one to two orders of magnitude compared to the corresponding p-type a-Si:H with the same boron concentration. Unlike phosphorus doping, a portion of the sulfur-related donors is passivated by hydrogen in the annealed state. This passivated portion can be rendered electrically active by optical excitation. This effect is similar to that which has been called persistent photoconductivity (PPC) and occurs in some compensated samples of a-Si:H and in some multilayer structures. The PPC effect has the opposite effect on both the photo- and dark conductivities from the Staebler-Wronski effect. For this reason it is possible to find an appropriate S/Si ratio where the two effects cancel as far as the conductivity is concerned. For an appropriate concentration of S in “intrinsic” a-Si:H one can obtain samples with high photoconductivity and essentially no degradation in either the dark or the photo-conductivities upon prolonged optical excitation (light soaking). These results suggest that at least the majority carriers are unaffected; however, it remains unclear what effect this second metastability will have on the minority carriers, and hence on PV device applications. The general idea that the addition of a second metastability to hydrogenated amorphous silicon (a-Si:H) might counteract the deleterious consequences of the Staebler-Wronski effect is presented.
3D Arrays of Quantum Dots for Laser Applications
Authors: Ledentsov N.N. , Böhrer J. , Bimberg D. , Zaitsev S.V. , Ustinov V.M. , Egorov A.YU. , Zhukov A.E. , Maximov M.V. , Kop'ev P.S. , Alferov ZH.I. , Kosogov A.O. , Gösele U. , Ruvimov S.S.
Published: April 2011

We have fabricated and studied injection lasers based on vertically coupled quantum dots (VECODs). VECODs are self-organized during alternate short-period GaAs-InAs (InGaAs) depositions after InAs (or InGaAs) pyramids are formed on a GaAs (100). The resulting arrangement represents laterally ordered array of nanoscale structures inserted in a GaAs matrix, where each structure is composed of several vertically merging InAs (or InGaAs) parts. VECODs are introduced in the active region of GaAs-AlGaAs double heterostructure laser. The threshold current density remarkably decreases with increase in number of periods (N) of the VECOD (down to 90 A cm-2 at 300K for N=10). The differential efficiency increases with N and the lasing occurs through ground state of quantum dot exciton up to room temperature (λ=1.05 μm).
Synthesis of GaAs Nano-Particles by Digital rf-sputtering
Authors: Hirasawa M. , Ichikawa N. , Egashira Y. , Komiyama H.
Published: April 2011

Nanometer-sized GaAs particles embedded in SiO2 were prepared by a digital rf-sputtering method, where GaAs and SiO2 targets were alternately sputtered in an Ar atmosphere. The GaAs deposition time was kept shorter than the time required to form a continuous layer. Transmission electron microscopy (TEM) observations showed that the sizes of the GaAs particles can be controlled from 2 to 8 nm by changing the sputtering cycle time of the GaAs target. In spite of their small size, the GaAs particles have crystallinity similar to the target material without substrate heating or post annealing. It was also revealed that the mechanism of the particle growth depend on the surface migration of the precursors. The optical absorption spectra of the GaAs particles show a blue shift as large as 1.6 eV, corresponding to strong quantum confinement of electrons and holes.
Photoluminescence Study of Chloride Vpe-Grown Gan
Authors: Ueda Tetsuzo , Yuri Masaaki , Lee Heon , Harris James S. , Baba Takaaki
Published: April 2011

We have examined the effect of growth conditions on photoluminescence (PL) characteristics of chloride VPE-grown GaN films. Undoped GaN films are grown on sapphire by a newly developed chloride VPE system which utilizes GaCl3 and NH3 as source materials.

We find that the spectra depend strongly on the growth temperatures and the corresponding surface morphology. Peaks from excitons and donor-acceptor pairs (D-A pair) recombination are observed for the films with terrace-like flat surfaces grown at between 950°C and 1000°C. A peak due to exciton bound to neutral donors is observed for a growth temperature of 975°C where the acceptor-related peaks are not seen. Decreasing the growth temperature below 950°C causes rough surfaces due to three-dimensional growth, whereas increasing the growth temperature above 1000°C causes cracks or partial pealing off of the film. The films with rough surfaces or crystal failures show broad emission from deep acceptor levels. As a result, residual acceptors are eliminated in the very narrow range of the growth temperature around 975°C. It is also noted that an increase of the V/III ratio during the growth makes the line width of the band-edge peak narrower. The PL results show that a growth temperature around 975°C and high V/III ratio are essential to obtain better crystal quality and reduced concentration of residual acceptors.
Vapor Phase Epitaxy of GaN Using Gallium Tri-Chloride and Ammonia
Authors: Yuri M. , Ueda T. , Lee H. , Itoh K. , Baba T. , Harris J.S.
Published: April 2011

GaN films with good crystalline quality are grown on sapphire by atmospheric pressure vapor phase epitaxy using gallium tri-chloride (GaCl3) and ammonia (NH3). Epitaxial growth is carried out over temperature and V/III-ratio ranges of 800–1000°C and 100–1000, respectively. Typical growth rate obtained is in the range of 5–20 μm/hr. The films grown below 925°C typically show three dimensional (island) growth, while above that temperature, continuous films are obtained. Films grown at 975°C with a V/III ratio > 300 exhibit a smooth surface. XRD analysis shows that the films are single crystal with hexagonal polytype. Strong band-edge photoluminescence is observed with a FWHM of 60 meV at room temperature and 25 meV at 77K. The results indicate that this simple growth technique is effective for growing high quality bulk GaN, which can be used as a substrate for subsequent epitaxy. In order to further improve the surface morphology, a preliminary experiment on GaN growth on a thin GaN buffer layer prepared by gas source MBE is also presented.
Characterization of the Solid-Phase Epitaxial Growth of Amorphized Gaas with In-Situ Electron Microscopy
Authors: Belay K. B. , Ridgway M. C. , Llewellyn D. J.
Published: April 2011

The influence of non-stoichiometry on the solid-phase epitaxial growth of amorphized GaAs has been studied with in-situ Transmission Electron Microscopy (TEM). Ion-implantation has been used to produce microscopic non-stoichiometry via Ga and As implants and macroscopic non-stoichiometry via Ga or As implants. It has been demonstrated that amorphous GaAs recrystallizes into a thin single-crystal layer and a thick heavily twinned layer. Video images of the recrystallization process have been quantified for the first time to study the velocity of the crystalline/amorphous (c/a)-interface as a function of depth and ion species. Regrowth rates of the single crystal and twinned layers as functions of non-stoichiometry have been calculated. The phase transformation is rapid in Ga-rich material. In-situ TEM results are consistent with conventional in-situ Time Resolved Reflectivity, ex-situ Rutherford Backscattering Spectroscopy and Channelling measurements and ex-situ TEM.
Damage Introduction in Ingap and Aigaas by Electron Cyclotron Resonance ar Plasmas
Authors: Lee J. W. , Pearton S. J. , Stradtmann R. R. , Abernathy C. R. , Hobson W. S. , Ren F.
Published: April 2011

Changes in sheet resistance of n- and p-type InGaP exposed to Electron Cyclotron Resonance Ar plasmas have been used to measure the introduction of ion-induced damage. P-type material is much more resistant to change in its conductivity than n-type InGaP, indicating that electron traps are the predominant entity produced by the ion bombardment. For short (˜1 min.) plasma exposures the ion current is more important than ion energy in producing resistance changes. Annealing of damage in both conductivity types occurs with an activation energy of ˜3.4±0.5eV. p+A1GaAs is found to be much more susceptible than n+AlGaAs to the introduction of electrically active deep levels during exposure to Electron Cyclotron Resonance Ar plasmas. In both AlGaAs materials the resistivity of thin (˜0.5μm) epitaxial layers increases rapidly with both plasma exposure time and the ion energy, while the ion density in the Ar discharge has a much greater influence on p+AlGaAs than n-type material. These results suggest that the energetic ion bombardment introduces deep hole traps more readily than deep electron traps in AlGaAs and that pnp transistor structures will be more susceptible to plasma damage than comparable npn structures.
Formation of New Semiconducting Ge-Si-Fe Alloy on Si(100) and its Optical Properties
Authors: Chen H. , Han P. , Huang X.D. , Hu L.Q. , Shi Y. , Zheng Y.D.
Published: April 2011

We report a new semiconducting Ge-Si-Fe alloy thin film grown on Si(100) by reactive deposition epitaxy(RDE) using high vacuum evaporation technique. AES and XRD results show that the new alloy can be regarded as a distorted β-FeSi2 with the Ge participation. The direct band gap of the Ge-Si-Fe alloy was determined to be 0.83eV by optical transmission measurement, which means a red shift of band gap compared with that of β-FeSi2 (Eg=0.87eV).
Gas-Source Molecular Beam Epitaxy of Electronic Devices
Authors: Beam E.A. , Brar B. , Broekaert T.P.E. , Chau H.F. , Liu W. , Seabaugh A.C.
Published: April 2011

Gas-source molecular beam epitaxy (GSMBE) has been developed into a useful tool for the growth of both optical and electronic device structures. In this paper, we report on the use of tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) in GSMBE for the growth of electronic device structures with state-of-the-art performance. Device structures based on both the In0.48Ga0.52P/GaAs and In0.53Ga 0.47As/InP lattice matched materials systems are described. The GSMBE system is based on the use of elemental Group-rn sources and employs thermal crackers for precracking TBA and TBP. Dopant sources include both elemental (Sn and Be) and vapor (CBr4 and SiBr4) sources. Device structures fabricated in the In0.48Ga0.52P/GaAs materials system include single- and double- heterojunction bipolar transistors (SHBTs and DHBTs). Device structures fabricated in the In0.53Ga0.47As/InP materials system include SHBTs, DHBTs, heterojunction field effect transistors (HFETs), and both planar and lateral resonant tunneling diodes (RTDs.) Vertically integrated HFET and multi-RTD heterostructures for high speed logic/memory are also described.
Mbe Growth and Properties of HgCdTe Long Wave and Very Long Wave Infrared Detectors
Authors: Rajavel R. D. , Wu O.K. , Jensen J.E. , Cockrum C.A. , Venzor G.M. , Patten E.A. , Goetz P.M. , Leonard D.B. , Johnson S.M.
Published: April 2011

structural, optical and electrical properties were evaluated. Significant progress has been made toward the growth of high performance HgCdTe devices by molecular beam epitaxy. Long wave infrared detectors operating at 9.9 μm at 78K exhibited a mean RoAoproduct of 1170 Ωcm2at 0-fov. Very long wave infrared detectors operating at 14 μm at 78K exhibited a mean RoA product of 3.5 Ωcm2at f/2 fov. These values represent the state-of-the- art for molecular beam epitaxially grown HgCdTe detectors.
Growth of Epitaxial Gan Films Using Zno Buffer Layer by Pulsed Laser Deposition
Authors: Huang T. F. , Tuncel E. , Yeo J. S. , Harris J. S.
Published: April 2011

GaN films and ZnO buffer layers have been deposited on c-cut sapphire substrates by pulsed laser deposition (PLD) employing a KrF laser (λ = 248 nm). The influence of the deposition parameters, such as substrate temperature and gas pressure during growth, have been studied. GaN films grown above 700 °C are single crystalline and the full width of half-maximum (FWHM) of the GaN (0002) peak decreases to 0.37° as the growth temperature increases to 800 °C. The optimum growth pressure for GaN is determined to be 0.01 torr N2. The optical transmission below the bandgap of the GaN film grown at this pressure is over 85%.
Structural Characterization of InAs/(GaIn)Sb Superlattices for IR Optoelectronics
Authors: Wagner J. , Schmitz J. , Fuchs F. , Weimar U. , Herres N. , Tränkle G. , Koidl P.
Published: April 2011

We report on the structural characterization of InAs/(GaIn)Sb superlattices (SL) grown by solid-source molecular-beam epitaxy. SL periodicity and overall structural quality were assessed by high-resolution X-ray diffraction and Raman spectroscopy. Spectroscopic ellipsometry was found to be sensitive to the (GaIn)Sb alloy composition.
Long-Wavelength Vertical-Cavity Surface-Emitting Laser Diodes
Authors: Babic D.I. , Jayaraman V. , Margalit N. M. , Streubel K. , Heimbuch M.E. , Mirin R.P. , Thibeault B.J. , Bowers J.E. , Hu E.L. , Denbaars S.
Published: April 2011

Long-wavelength (1300/1550 nm) vertical-cavity surface-emitting lasers (VCSELs) have been much more difficult to realize than VCSELs at shorter wavelengths such as 850/980 nm. The primary reason for this has been the low refractive index difference and reflectivity associated with lattice-matched InP/InGaAsP mirrors. A solution to this problem is to “wafer-fuse” high-reflectivity GaAs/AlGaAs mirrors to InP/InGaAsP active regions. This process has led to the first room-temperature continuous-wave (CW) 1.54 μm VCSELs. In this paper, we discuss two device geometries which employ wafer-fused mirrors, both of which lead to CW operation. We also discuss fabrication of WDM arrays using long-wavelength VCSELs.
Stabilization of Transverse Mode Emission in Vertical-Cavity Surface-Emitting Lasers by Deposition of High Refractive Index Amorphous Gaas
Authors: Park Hyo-Hoon , Yoo Byueng-Su , Chu Hye Yong , Lee El-Hang , Park Min Soo , Ahn Byung Tae , Shin Jae-Heon , Lee Yong Hee
Published: April 2011

We report successful application of a low-temperature-grown amorphous GaAs (a-GaAs) layer for stabilization of the fundamental transverse mode of InGaAs/GaAs vertical-cavity surface-emitting lasers. The maximum currents maintaining a stable fundamental transverse mode were increased by the antiguide effect of a-GaAs with a high refractive index. For 10-μm- and 15-μm-diameter devices, we attained a stable single-mode emission over a wide range of current. The antiguiding of transverse modes in vertical cavity buried in the high refractive cladding layer was calculated using a two-dimensional beam propagation method.
Orientation Dependence Of Surface Passivation For Semi-Insulating Gaas
Authors: Koutzarov I.P. , Edirisinghe C.H. , Ruda H.E. , Jedral L.Z. , Liu Q. , Guo-Ping J. , Xia H. , Lennard W. N. , Rodriguez-Fernandez L.
Published: April 2011

We report on the orientation dependence ((100), (110) and (111) ) of photoluminescence (PL), photoreflectance (PR) and Surface Photo-Voltage (SPV) for sulfur passivated bulk semiinsulating (SI) GaAs. Near band gap PL peak intensities (bound-exciton and acceptor-related) were enhanced following (NH4)2S or S2Cl2 treatment of GaAs for all orientations. The reduction of surface recombination velocity (from PL data) was orientation dependent and especially pronounced for the case of (111)A and (111)B orientations. The effect of thin dielectric layers deposited on S-treated surfaces was also investigated, particularly for (100) and (111)A orientations. SPV data shows a strong increase in the above band gap signal after both Streatment and dielectric film deposition, which was higher than that measured for only S-treated surfaces. PR data showed an increase in the interfacial electric field following deposition of dielectric film. The results of absolute S-surface coverage measurements using particle-induced X-ray emission measurements were correlated with the optical characteristics.
Factors Governing the Photoluminescence Yield of Erbium Implanted Silicon
Authors: Jantsch W. , Przybylinska H. , Skierbiszewski C. , Lanzerstorfer S. , Palmetshofer L.
Published: April 2011

We present a high resolution photoluminescence (PL) study of Si:Er which allows to distinguish a variety of Er centers occurring in Er-implanted Si. The lines belonging to a particular center are identified from the influence of processing parameters, temperature, excitation power, co-doping and hydrostatic pressure. The center-dependent high temperature yield is limited by the competition in efficiency of capturing excitons at Er centers or nearby defects followed by the excitation transfer to the Er-4f shell and by recombination of excitons at other, non-radiative centers. The excitation transfer probability is shown to depend on hydrostatic pressure of a few kbar. This effect indicates a new possibility to improve the efficiency of Si:Er light emitters.
The Effects of Impurity Codoping on the Electrical Properties of Erbium Ions in Crystalline Silicon
Authors: Libertino S. , Coffa S. , Mosca R. , Gombia E.
Published: April 2011

We have investigated the effects of oxygen codoping and thermal annealing on the deep level spectrum and carrier lifetime of Er implanted crystalline Si. It is found that oxygen codoping produces a dramatic modification in the concentration and energetic position of Er-related deep levels in the Si band gap. In particular the formation of Er-O complexes is shown to produce a promotion from deep to shallow levels. This effect is the major responsible of the enhancement of Er donor behaviour in presence of oxygen and also produces a large increase in the minority carrier lifetime
Photoluminescence of Erbium Implanted in SiGe
Authors: Chang S. J. , Nayak D. K. , Shiraki Y
Published: April 2011

The optical properties of an Er-implanted SiGe sample have been studied Sharp and temperature-stable Er-related PL peaks were observed at around 1.5pm, which correspond to the Er 4I13/2 to 4I15/2 transition. It was found that the Er ions form more than three noncubic luminescence centers in the SiGe host. Although the PL intensity quenches at high temperatures, the Errelated PL signal can still be observed at room temperature. For a Si0.87Ge0.13:Er sample annealed at 850°C for 20 min, the activation energy is 130 meVwhich is slightly smaller than that of the Er-doped Si.
Characterization of Visible and Infrared (1.54 μm) Luminescence from Er-doped Porous Si
Authors: White R. , Wu X. , Hömmerich U. , Namavar F. , Cremins-Costa A. M.
Published: April 2011

Results of a photoluminescence excitation (PLE) study of Er-implanted porous Si (Er: PSi) are presented. Erbium was implanted at a dose of 1×1015 Er/cm2 at 380 keV and annealed for 30 minutes at 6507deg;C. We observed a nearly identical PLE intensity behavior from 1.54 μm and visible-emitting Er: PSi. This observation indicates that both visible and infrared photoluminescence (PL) arise from carrier mediated processes, and that the 1.54 μm Er3+ PL is related to the porous Si nanostructures. Measurements of the temperature dependence (15–375K) of Er3+ PL intensity and lifetime are also reported.
Luminescence of Rare Earth Doped Porous Silicon
Authors: Kimura T. , Hosokawa I. , Nishida Y. , Dejima T. , Saito R. , Ikoma T.
Published: April 2011

Photoluminescence characteristics of porous silicon layers (PSLs) doped with Er or Yb ions are studied. 10μm thick PSLs with a luminescence centered at ∼ 0.8μm are formed by anodic etching of p-type silicon wafers of several Ω-cm resistivity. Rare-earth ions are electrochemically incorporated into PSLs. The Er3+-related luminescence at 1.54μm as well as the Yb3+-related luminescence at 1.0μm is observed at room temperature after annealing at high temperatures (>900°C). The Er-related luminescence is enhanced after annealing in O2, whereas the Yb3+-related luminescence needs oxygen-free atmosphere (H2) for the optical activation. The luminescence decay time of the rare earth ions as well as the host PSLs is measured and the energy transfer mechanism is discussed.
Study of the Zeeman Effect of Er3+ in GaAs:Er,O
Authors: Haase Dieter , Dörnen Achim , Takahei Kenichiro , Taguchi Akihito
Published: April 2011

We analyze the Zeeman effect of the 4/13/2 → 4/15/2 transition of Er3+ in GaAs:Er,O grown by metal-organic vapor-phase epitaxy. The photoluminescence spectrum has been assigned previously to one specific Er-O complex. The dominant optical transition at 1538 nm (6499.5 cm−1), which shows a full width at half maximum of only 0.05 cm−1, has been investigated by high-resolution Zeeman spectroscopy. A highly anisotropic Zeeman pattern is found which indicates the low symmetry of the underlying complex. A detailed analysis shows that the defect has a predominant rhombic symmetry C2v,. Additionally, smaller contributions of a crystal field with a monoclinic symmetry Clh are found. The results provide further arguments that an ErO2 complex is the responsible center observed.
Characterization Of Er-Doped III-V Nitride Epilayers Prepared by Mombe
Authors: Zavada J. M. , Wilson R. G. , Schwartz R. N. , MacKenzie J. D. , Abernathy C. R. , Pearton S. J. , Wu X. , Hömmerich U.
Published: April 2011

Er-doped AIN epilayers have been grown using metal-organic molecular beam epitaxy (MOMBE) with controlled Er densities. Cell temperatures greater than 1000°C were required for the Er solid source in order to achieve significant Er concentrations in the epilayers. Er densities in the 1019 to 1020 cm−3 range were confirmed using secondary ion mass spectrometry (SIMS), quantified using implanted standards. The epilayers were optically excited using an argon-ion laser and infrared luminescence spectra were measured over the temperature range 13 to 300 K. The spectra are centered at 1.54 μm and display features typical of the Er3+ configuration. These data demonstrate that high densities of Er atoms can be incorporated in AIN films during epitaxial growth and that the Er atoms give rise to the intra-4f transitions of the trivalent Er3+ ion.
Annealing Study of Erbium and Oxygen Implanted Gallium Nitride
Authors: Torvik John T. , Feuerstein Robert J. , Qiu Chang H. , Leksono Moeljanto W , Pankove Jacques I. , Namavar Fereydoon
Published: April 2011

A systematic study of photoluminescence (PL) of Er and O ion implanted and annealed n-type GaN grown on R-plane sapphire (A12O3) was performed. The Er implants ranged from 2 × 1013 to 1 × 1015 Er++/cm2, and the O co-implants ranged from 1014 to 1016 O+/cm2. The resulting nine different combinations of GaN:Er,O were annealed at 600 °C (4 hrs. in N2), 700 °C (1.5 hrs. in N2), 800 °C (0.75 hr. in NH3), and 900 °C (0.5 hr. in NH3) Following each annealing step, the Er3 -related PL at 1.54 μm was measured from each sample at 77K, when pumped directly with 135 mW of power at 980 nm. The three samples with the highest dose of Er (1 × 1015 Er++/ cm 2), regardless of O co-dopant dose, yielded the strongest PL peak intensity at 1.54 μm after all the anneals. The integrated PL from 1.52 to 1.58 μm was reduced by 62 % when going from 77 K to room temperature (RT).
Rare-Earth Doped Epitaxial InGaP and its Optical Properties
Authors: Wessels B. W.
Published: April 2011

The optical properties of rare-earth impurities in InGaP and the factors which influence their luminescence efficency are presented. Basic energy transfer processes are described. Practical devices that utilize characteristic rare-earth luminescence are reported.
Energy-Transfer Processes in Oxygen-Codoped GaAs:Er
Authors: Takahei K. , Hogg R. A. , Taguchi A.
Published: April 2011

GaAs grown by metalorganic chemical vapor deposition and codoped with Er and oxygen shows a simple spectrum with sharp luminescence lines due predominantly to one type of Er center. This center is identified as an Er atom substituting a Ga site, coupled with two oxygen atoms. Photoluminescence measurements under host excitation and photoluminescence excitation measurements that directly excite the 4f-shell of the Er3+ ion indicate that this center is excited much more efficiently than other Er centers simultaneously present in the same sample. A possible energy-transfer mechanism and its implications are discussed.
Excitation Properties of Er-Doped GaP from Photoluminescence and High Pressure Studies
Authors: Culp T. D. , Wang X. Z. , Kuech T. F. , Wessels B. W. , Bray K. L.
Published: April 2011

The photoluminescence properties of MOCVD GaP:Er were investigated as a function of temperature, applied hydrostatic pressure, and excitation wavelength. Four sharp peaks are observed on the high energy side of the 1.54 μm Er3+ emission. These peaks are selectively excited by below-gap energies and have a significantly shorter lifetime than the main Er3+ emission, suggesting that at least two distinct Er3+ centers contribute to the luminescence. The low temperature photoluminescence excitation (PLE) spectrum of the 1.54 μm emission was also measured. Strong broad excitation of the Er3+ centers occurs with energies well below the indirect bandgap energy. In fact, the Er3+ emission intensity is significantly stronger when excited with below-gap wavelengths than with above-gap wavelengths. This result has been explained in terms of competition between Er3+ excitation and nonradiative deep level recombination for free carriers under above-gap excitation. With below-gap excitation, carriers are promoted directly into the Er3+ excitation pathway via absorption at an erbium-related trap. At 42 kbar, below-gap excitation is no longer more efficient than above-gap excitation, suggesting that competitive capture of free carriers by deep levels has been reduced.
1.54 μm Electroluminescence from Erbium Doped Gallium Phosphide Diodes
Authors: Ford G. M. , Wessels B. W.
Published: April 2011

Er-doped GaP diodes that exhibit strong room temperature characteristic 4f-shell luminescence under forward bias have been fabricated. The output of the diode increases linearly with current for low current densities but eventually saturates. The radiative decay lifetime is 2.6 msec and is independent of current. It is proposed that the observed intensity dependence on excitation power results from saturation of the optically active Er3+ centers. Some diodes showed a superlinear dependence, with a threshold of about 2 A/cm2.
Erbium Doped GaAs by Mocvd
Authors: Greenwald A. C. , Linden K. J. , Rees W. S. , Just O. , Haegel N. M. , Donder S.
Published: April 2011

The overall objective of this research is to develop temperature stable 1.54 ptm light sources based upon ionic emitters. LEDs and diode lasers were fabricated in MOCVD grown AIGaAs materials but only weak electroluminescence was observed. The III-V compound semiconductors were doped with erbium amide sources of the form: Er{N[Si(CH 3)3]R}3 where R s an organic unit. These amide sources had reduced carbon and oxygen levels in a GaAs film compared to the use of a cyclopentadienyl erbium source, but did dope the semiconductor with silicon. Silicon doping levels were a function of growth temperature. Erbium photoluminescence was enhanced with oxygen codoping, but diode electrical characteristics were degraded. PLE showed that erbium ions were excited by above bandgap light absorbed by GaAs.
Improved Nickel Silicide Ohmic Contacts to N-Type 4H and 6H-SiC Using Nichrome
Authors: Luckowski E. D. , Williams J. R. , Bozack M. J. , Isaacs-Smith T. , Crofton J.
Published: April 2011

Results are reported for ohmic contacts formed on n-type 4H and 6H-SiC using nichrome (80/20 weight percent Ni/Cr). In comparison to contacts formed on 6H-SiC using pure Ni, the electrical characteristics of these NiCr contacts are similar (∼ 1E-5 Ω-cm2 for moderately doped material), and composite Au/NiCr contacts exhibit good stability during long-term anneals (∼ 2500 hr) at 300 C without the requirement of a diffusion barrier layer between the ohmic contact layer and the Au cap layer. The use of NiCr also results in success rates near 100% for direct wire bonding to the Au cap layers.
Low Resistance Ohmic Contact on p-type GaN Grown by Plasma-Assisted Molecular Beam Epitaxy
Authors: Yoo Myung C. , Lee J. W. , Myoung J. M. , Shim K. H. , Kim K.
Published: April 2011

Ohmic contacts on p-type GaN have been investigated. High quality GaN epilayers on cplane sapphire were prepared using plasma-assisted molecular beam epitaxy that utilized an inductively coupled rf nitrogen plasma source and solid source beams. The resulting film thickness and the doping concentration of the grown samples were in the range of 0.7–1.35 μm and 1018 – 1020/cm3, respectively. The metallization consisted of high work function metal bilayers which included a combinations of 25 nm-thick Ni, Ti, Pt and/or Cr and 200 nm-thick Au on the highly p-doped GaN in a transmission line model pattern. Ohmic contacts were formed by alloying the bi-layers using rapid thermal annealing (RTA) at temperatures in the range of 300–700 °C for 1 min under nitrogen ambient. Current-voltage measurements showed that the specific contact resistance was as low as 1.2 × 10 −4 Ω–cm2 for the sample having 1.4 × 1020/cm3p-type doping concentration with a Cr/Au contact annealed at 500 °C for 1 min by RTA. Judging from the scanning Auger microscopy results and the glancing angle x-ray diffraction analysis, this resistance is attributed to Cr diffusion into the GaN layer.
Optical Spectroscopy of Dry-Etched GaN-Nanostructures
Authors: Zull H. , MÜller J. , Koeth J. , Kieseling F. , Forchel A.
Published: April 2011

We have realized GaN wire gratings with periods down to 80 nm and with wire widths down to 26 nm- GaN layers of good structural and optical quality with thicknesses down to 100 nm were grown by electron cyclotron resonance assisted MBE (ECR-MBE). The grating structures were fabricated by high resolution electron beam lithography and electron cyclotron enhanced reactive ion etching (ECR-RIE) using CL2/Ar as etching gas. The optical properties of the GaN structures were investigated by photoluminescence (PL) spectroscopy in the temperature range between 40 K and 110 K. The wire patterns show intense excitonic photoluminescence and only a small dry etched induced degradation of the quantum efficiency even for the narrowest wires.
Si Implantation and Annealing OF GaN FOR n-Type Layer Formation
Authors: Molnar B. , Wickenden A. E. , Rao M. V.
Published: April 2011

High dose Si has been implanted into MOCVD grown high resistivity and n-type GaN in the 26–500°C temperature range. The implant activation varies widely (30 −>100%) depending on, what energy level is assigned to the Si, the implantation and annealing temperatures, and the quality of the substrate. The usable maximum temperature for activation is limited by the severe decomposition of the GaN. After 1050°C 15s RTA Ga liquid droplet formation has been observed by SEM. This decomposition changes the surface morphology but did not introduce measurable change in the electrical properties up to 1150°C /120s RTA.
P-And N-Type Implantation Doping Of GaN With Ca And O
Authors: Zolper J. C. , Wilson R. G. , Pearton S. J. , Stall R. A.
Published: April 2011

III-N photonic devices have made great advances in recent years following the demonstration of doping of GaN p-type with Mg and n-type with Si. However, the deep ionization energy level of Mg in GaN (∼160 meV) limits the ionized of acceptors at room temperature to less than 1.0% of the substitutional Mg. With this in mind, we used ion implantation to characterize the ionization level of Ca in GaN since Ca had been suggested by Strite [1] to be a shallow acceptor in GaN. Ca-implanted GaN converted from n-to-p type after a 1100°C activation anneal. Variable temperature Hall measurements give an ionization level at 169 meV. Although this level is equivalent to that of Mg, Ca-implantation may have advantages (shallower projected range and less straggle for a given energy) than Mg for electronic devices. In particular, we report the first GaN device using ion implantation doping. This is a GaN junction field effect transistor (JFET) which employed Ca-implantation. A 1.7 µm JFET had a transconductance of 7 mS/mm, a saturation current at 0 V gate bias of 33 mA/mm, a ft of 2.7 GHz, and a fmax of 9.4 GHz. 0-implantation was also studied and shown to create a shallow donor level (∼25 meV) that is similar to Si. SIMS profiles of as-implanted and annealed samples showed no measurable redistribution of either Ca or0inGaNat 1125°C.
Tem Structure Characterization Of Ti/Al and Ti/Al/Ni/Au Ohmic Contacts For n-GaN
Authors: Ruvimov S. , Liliental-Weber Z. , Washburn J. , Duxstad K. J. , Hailer E. E. , Fan Z.-F. , Mohammad S. N. , Kim W. , Botchkarev A. E. , Morkoq H.
Published: April 2011

Transmission electron microscopy has been applied to characterize the structure of Ti/Al and Ti/Al/Ni/Au ohmic contacts on n-type GaN (˜1017 cm−3 ) epitaxial layers. A thin polycrystalline cubic TiN layer epitaxially matched to the (0001) GaN surface was detected at the interface with the GaN substrate. This layer was studied in detail by electron diffraction and high resolution electron microscopy. The orientation relationship between the cubic TiN and the GaN was found to be: {111}TiN//{00.1}GaN, [110]TiN//[11.0]GaN, [112 ]TiN//[ 10.0]GaN. The formation of this cubic TiN layer results in an excess of N vacancies in the GaN close to the interface which is considered to be the reason for the low resistance of the contact.
Analysis of the Sublimation Growth Process of Silicon Carbide Bulk Crystals
Authors: Eckstein R. , Hofmann D. , Makarov Y. , Müller St. G. , Pensl G. , Schmitt E. , Winnacker A.
Published: April 2011

Experimental and numerical analysis have been performed on the sublimation growth process of SiC bulk crystals. Crystallographic, electrical and optical properties of the grown silicon carbide (SIC) crystals have been evaluated by various characterization techniques. Numerical models for the global simulation of SiC bulk growth including heat and mass transfer and chemical processes are applied and experimentally verified.
Growth of Crystalline Quality Sic on Thin and Thick Silicon-on-Insulator Structures
Authors: Namavar F. , Colter P. , Gagnon E. , Cremins-Costa A. , Perry D. , Pirouz P. , Wu C-H.
Published: April 2011

We have grown silicon carbide (SiC) on ultrathin Si (about 300Å) and on thick Si (about 2000Å) on commercial SIMOX (from IBIS Corp and SOITEC, Inc.), and bulk Si. Electron diffraction and Rutherford backscattering spectroscopy (RBS)/channeling studies indicate epitaxial growth of singlecrystal β-SiC even at growth temperatures as low as 1100°C.

We have already demonstrated the fabrication of ultrathin Si, as thin as 140Å on SiO2 by using the low-energy SIMOX (LES) (20 to 30 keV) process to produce films of lower cost and excellent integrity compared to thinned commercial SIMOX. Based on these results, ultrathin Si-on-insulator (SOI) substrates appear to have great potential for device quality SiC films. However, the carbonization and/or growth of SiC on ultrathin Si requires further optimization because the processes for surface cleaning and growth of SiC on bulk Si substrates cannot be applied because of the thinness of the substrate layers. Additional carbonization work at higher temperatures has indicated the possibility of converting the entire Si top layer.
High Temperature Gas Phases Reactions Of Trimethylgallium with Ammonia and Trimethylamine
Authors: Thon A. , Safvi S. A. , Kuech T. F.
Published: April 2011

The use of trimethylgallium-trimethylamine (TMG:TMN) adduct as alternative cation precursor for MOVPE of GaN was studied by means of in-situ mass spectroscopy in an isothermal flow tube reactor. The temperature, pressure and reaction time were chosen to emulate the gas phase environment typical of the metal-organic vapor phase: epitaxy (MOVPE) of GaN. Dynamic changes in the mass spectra are reported for the gas phase reactions between trimethylgallium (TMG) and TMN in hydrogen (H2/D2) and ammonia (NH3/ND3) ambients. Evidence presented for the high temperature TMG:TMN adduct formation, followed by ethane elimination. The strength of the adduct bonding is comparable to that of TMG:NH3 and thus suppresses TMN displacement by ammonia. The thermal stability of TMG:TMN was found to be higher in ammonia ambient than it is in hydrogen. Kinetic parameters for some of the decomposition processes are given.
Electrical and optical investigation of the position of vanadium related defects in the 4H and 6H SiC bandgaps
Authors: Jenny J. R. , Skowronski M. , Mitchel W. C. , Smith S. R. , Evwaraye A. O. , Hobgood H. M. , Augustine G. , Hopkins R. H.
Published: April 2011

Hall effect, deep level transient spectroscopy, optical absorption, and optical admittance spectroscopy were employed to determine the position of the vanadium acceptor and vanadiumnitrogen complex in vanadium- and nitrogen-doped 4H and 6H SiC. Hall effect results indicate that the acceptor position in 4H(6H) SiC is 0.80(0.66) eV beneath the conduction band edge. The DLTS signature of the defect in the 4H polytype showed an ionization energy of 806 meV and a capture cross section of 1.8×10−16 cmr−2 The optical absorption measurements proved that the acceptor level investigated is related to isolated vanadium, and therefore the vanadium acceptor level. Based upon DLTS and SIMS measurements, the maximum solubility of vanadium in SiC was determined to the 3×10−17 crn3. An examination of polarized light experiments indicates that vanadium also complexes with another element to form electronic(at 5000 cm−1) and vibrational absorption(at 683 cm−1) bands. While the other constituent cannot be identified, evidence suggests that nitrogen is a likely candidate. This complex introduces a deep level at Ec−0.78 eV as determined using optical admittance spectroscopy.
Structure of the 2H-Ain/6H-SiC Interface
Authors: Vermaut P. , Ruterana P. , Nouet G. , Morkoç H.
Published: April 2011

Steps at the AIN/SiC interface have been investigated by HREM. Some of them do not introduce any defects. Others steps present a dislocation character which can contribute to relieve the strain due to the lattice mismatch. A third kind of steps gives rise to a prismatic planar fault for which a model is given. A reaction between prismatic and basal stacking faults is analyzed.
Defect Dominant Junction Characteristics of 4H-SiC p+/n Diodes
Authors: Scofield J. , Dunn M. , Reinhardt K. , Yeo Y. K. , Hengehold R.
Published: April 2011

Forward and reverse current-voltage (I-V-T) measurements of MOCVD grown 4H-SiC p+/n diodes are compared to classical recombination-generation theory over the temperature range of 100 to 750 K. The forward bias data indicate that the I-V characteristics of the wellbehaved devices follow a classical recombination dominant transport mechanism. Ideality factors were determined to be in the range of 1.85 to 2.09, and the forward activation energy found to be EA = l.56 eV compared to a nearly ideal value of 1.6 eV. A majority of the devices tested under forward bias conditions were, however, found to exhibit significant leakage current components due to tunneling at forward biases of up to 2.2 V for turn-on voltages in the 2.5 to 3.0 range. Deep level transient spectroscopy (DLTS) was also performed on the diode structures over the same wide temperature range, and the results were correlated to those obtained from reverse I-V-T and C-V-T characterization. Deep level defects at energies between 200 and 856 meV were identified from the DLTS data, and these levels are believed to be responsible for the tunneling dominant current conduction. Intrinsic deep levels, common to all devices tested, are emphasized and suggested as possible reverse bias tunneling paths for breakdown to explain the lack of an avalanche mechanism in all of the 4H-SiC diodes tested.
Theory and Realization of a Two-Layer Hall Effect Measurement Concept for Characterization of Epitaxial and Implanted Layers of SiC
Authors: Schöner Adolf , Rottner Kurt , Nordell Nils
Published: April 2011

Epitaxial and implanted layers are generally characterized by Hall effect measurements using a pn-junction as electrical insulation of the layer from the substrate. Due to defects, low doping concentrations or thin layers the resistivity of epitaxial or implanted layers is comparable to the resistivity of the pn-junction and the substrate. This results in inefficient electrical insulation between both regions. To be able to determine the properties of epitaxial or implanted layers even in the case of substantial leakage current we developed a two-layer Hall effect measurement concept. This concept is based on the conventional van der Pauw technique applied to the layer and the substrate separately. In addition the current-voltage characteristic of the pn-junction is measured and modeled in the analysis as an ohmic resistor.

This two-layer concept is applied to epitaxial grown SiC and the results are compared with conventional van der Pauw technique. In addition both techniques are compared with the results of capacitance-voltage (CV) measurements and secondary ion mass spectroscopy (SIMS).
A Study of Electroluminescent Emission from CVD Diamond
Authors: Manfredotti C. , Fizzotti F. , Vittone E. , Polesello P. , Wang F. , Schwarz R. , Grebnert S.
Published: April 2011

CVD diamond could be an electroluminescent material. While its photoluminescent and cathodoluminescent properties are relatively well known, the electroluminescent ones have not been intensively investigated. The electroluminescent emission of CVD diamond is reminescent of the so-called “band A”; it is centered at 2.8 eV and extends from 2.6 to 3 eV. The luminescenceintensity increases linearly with the electric current and corresponds to a superquadratic regime of I-V characteristics in the dark and to a quadratic regime under a λ = 442 nm illumination. The I-V characteristics can be related to space charge limited current (SCLC) phenomena. Besides, the temperature behaviour of electroluminescence and of photoexcited current can be put into relation with the presence of a deep state in the bandgap where injected carriers from both electrodes recombine. The electroluminescent emission, even in a wavelength region far away from the photopic response, is clearly and strongly visible at naked eye. The luminescence efficiency is being discussed in order to consider CVD diamond as a material for optoelectronic devices.
Cathodoluminescence Studies of Bound Excitons and Near Band Gap Emission Lines in Boron- and Phosphorus-Doped CVD-Diamonds
Authors: Sternschulte H. , Albrecht T. , Thonke K. , Sauer R. , Grieβer M. , Grasserbauer M.
Published: April 2011

Cathodoluminescence measurements at cryogenic temperatures are reported on boron- and phosphorus-doped CVD-diamond films grown on silicon substrates. Boron and phosphorus concentrations were determined by SIMS measurements; for boron, they reached from unintentional background doping levels up to 3500 ppm. At increasing boron concentrations, the radiative recombination of boron bound excitons (BEto) at 5.22 eV photon energy systematically broadens and shifts down to 4.99 eV whereas the free exciton emission (FEto) disappears for 40 ppm and higher. In the phosphorus-doped films we observe new lines at 5.16 eV and 4.99 eV which we ascribe to TO- and (TO+Or)-phonon assisted transitions of an exciton bound to a shallow impurity other than boron, possibly phosphorus or a phosphorus-related shallow complex.
Photoreflectance Study of Gan Film Grown by Metalorganic Chemical Vapor Deposition
Authors: Yang K. , Zhang R. , Zheng Y. D. , Qin L. H. , Shen B. , Shi H. T. , Huang Z. C. , Chen J. C.
Published: April 2011

Photoreflectance was used to study the optical properties of single crystal hexagonal GaN film on (0001) sapphire substrate grown by metalorganic chemical vapor deposition. The energy gap of GaN was determined as 3.400 eV, and the possible origin of the PR signal was attributed to the modulation of the surface field and lineshape broadening of defects. Optical absorption and cathodoluminescence of the GaN sample were measured, and the optical absorption edge of 3.39 eV and the cathodoluminescence emission peak of 3.461 eV at low temperature (15.6K) confirmed the results of Photoreflectance.
Pyroelectric Effect in Wurtzite Gallium Nitride
Authors: Bykhovski A. D. , Kaminski V. V. , Shur M. S. , Chen Q. C. , Khan M. A.
Published: April 2011

We report on the measurements of the pyroeffect in wurtzite n-type GaN films deposited over basal plane sapphire substrates. The voltage drop between the contacts was measured while the sample was subjected to uniform heating. Our results show that the pyroelectric effect in GaN can be partially attributed to the secondary pyroelectricity, caused by the development of strain in the material due to thermal expansion.
Optical and Structural Properties of α-Si1-xCx Films
Authors: Chen Zhizhong , Yang Kai , Zhang Rong , Shi Hongtao , Zheng Youdou
Published: April 2011

In this paper, we reported experimental results about optical and structural properties of amorphous silicon carbide (α-Si1-xCx). The films of a-Si1-xCx) were grown by CVD on substrate of quartz glass. Optical constants (n-refractive index, a-absorption coefficient, Eg-optical energy band gap) of these films were determined by transmission spectra. The radial distribution functions (RDFs) of α- Sil−xCx) films were drawn out from the data of x-ray diffraction spectra. According to the RDFs, we imagined the statistic scene from which we could obtain the information of atomic radial distribution. The bond lengths and bond numbers of Si-Si, Si-C, and C-C could be also determined by RDFs. From the analysis of Raman spectra, we obtained the information of their vibration state density, and discerned the peaks of bond vibration, which agreed well with the results of α-Si1-xCx) RDF.
Investigation of the Field Emission Current from Polycrystalline Diamond Films
Authors: Glesener J. W. , Morrish A. A.
Published: April 2011

The field emission current from boron doped polycrystalline diamond films was characterized as a function of voltage and temperature. The motivation for the current-temperature measurements was to assess the thermal stability of the diamond emitters and gain some insight into a possible emission mechanism.

Results from the current-temperature (I-T) measurements found that the field emission current appeared independent of temperature. The best characterization of the results implied a temperature independent electron tunneling mechanism if not electron emission from the valence band of diamond.
Critical Materials, Device Design, Performance and Reliability Issues in 4H-SiC Power Umosfet Structures
Authors: Agarwal A. K. , Siergiej R. R. , Seshadri S. , White M. H. , McMullin P. G. , Burk A. A. , Rowland L. B. , Brandt C. D. , Hopkins R. H.
Published: April 2011

The long-term reliability of gate insulator under high field stress of either polarity presents a constraint on the highest electric field that can be tolerated in a 4H-SiC UMOSFET under on or off condition. A realistic performance projection of 41H-SiC UMOSFET structures based on electric field in the gate insulator (1.5 MV/cm under on-condition and 3 MV/cm under offcondition) consistent with long-term reliability of insulator is provided for the breakdown voltage in the range of 600 to 1500 V. The use of P+ polysilicon gate allows us to use a higher field of 3 MV/cm in the insulator under off-condition and leads to a higher breakdown voltage as the Fowler Nordheim (FN) injection from the gate electrode is reduced. FN injection data is presented for p type 4H-SiC MOS capacitor under inversion at room temperature and at 325°C. It is concluded that the insulator reliability, and not the SiC, is the limiting factor and therefore the high temperature operation of these devices may not be practical.