57 Matching Results

Search Results

Advanced search parameters have been applied.

Upconversion of near GaAs bandgap photons to GaInP{sub 2} emission at the GaAs/(ordered) GaInP{sub 2} heterojunction

Description: The authors have observed upconversion of photoluminescence in several partially ordered GaInP{sub 2} epilayers grown on [100] oriented GaAs substrates. They found that this upconversion occurs even when the excitation photon energy is below the bandgap of GaAs but near the electron-acceptor transitions at {approximately} 1.49 eV. A two-step two-photon absorption model in which the conduction band alignment at the GaAs/GaInP{sub 2} is of type 2 is proposed to explain the results.
Date: September 1, 1996
Creator: Teo, K.L.; Su, Z.P.; Yu, P.Y. & Uchida, K.
Partner: UNT Libraries Government Documents Department

Spectroscopic study of partially-ordered semiconductor heterojunction under high pressure and high magnetic field

Description: Photoluminescence upconversion (PLU) is a phenomenon in which a sample emits photons with energy higher than that of the excitation photon. This effect has been observed in many materials including rare earth ions doped in insulating hosts and semiconductor heterostructures without using high power lasers as the excitation source. Recently, this effect has been observed also in partially CuPt-ordered GaInP{sub 2} epilayers grown on GaAs substrates. As a spectroscopic technique photoluminescence upconversion is particularly well suited for studying band alignment at heterojunction interface. The value of band-offset has been determined with meV precision using magneto-photoluminescence. Using the fact that the pressure coefficient of electrons in GaAs is higher than those in GaInP{sub 2} they have been able to manipulate the band-offset at the GaInP/GaAs interface. By converting the band-offset from Type I to Type II they were able to demonstrate that the efficiency of the upconversion process is greatly enhanced by a Type II band-offset.
Date: December 31, 2000
Creator: Yu, P.Y.; Martinez, G.; Zeman, J. & Uchida, K.
Partner: UNT Libraries Government Documents Department

Characterization of the structure and polarity of twin boundaries in GaP

Description: The structure of planar defects in GaP films grown by MBE on Si (110) was investigated by transmission electron microscopy. Growth of GaP films on the (110) surface produced numerous microtwins which formed both first and second order twin boundaries. Using high-resolution transmission electron microscopy, the atomic structure of {Sigma} = 3 and {Sigma} = 9 twin boundaries were studied. Both the {Sigma} = 3 and {Sigma} = 9 interfaces were observed to facet along specific crystallographic planes. Geometric models of the {Sigma} = 9 {l_brace}221{r_brace} twin boundary accounting for different polar bonding configurations were proposed and compared with experimental observations.
Date: April 1, 1998
Creator: Cohen, D.; Medlin, D.L. & Carter, C.B.
Partner: UNT Libraries Government Documents Department

Reactive Ion Beam Etching of GaAs and Related Compounds in an Inductively Coupled Plasma of Cl(2)-Ar Mixture

Description: Reactive ion beam etching (RD3E) of GaAs, GaP, AIGaAs and GaSb was performed in a Cl2-Ar mixture using an Inductively Coupled Plasma (ICP) source. `The etch rates and yields were strongly affected by ion energy and substrate temperature. The RJBE was dominated by ion-assisted etching at <600 eV and by physical sputtering beyond 600 eV. The temperature dependence of the etch rates revealed three different regimes, depending on the substrate temperature: 1) sputtering-etch limited, 2) products-resorption limited, and 3) mass-transfer limited regions. GaSb showed the overall highest etch rates, while GaAs and AIGaAs were etched at the same rates. The etched features showed extremely smooth morphologies with anisotropic sidewalls.
Date: November 23, 1998
Creator: Abernathy, C.R.; Hahn, Y.B.; Hays, D.; Lambers, E.S.; Lee, J.W.; Pearton, S.J. et al.
Partner: UNT Libraries Government Documents Department

Quantum confinement in GaP nanoclusters

Description: We have prepared GaP and GaAs nanoclusters from organometallic condensation reactions of E[Si(ChH{sub 3})3]3 (E = P, As) and GaCl{sub 3}. The size of the as synthesized clusters is 10 {Angstrom} to 15 {Angstrom}. Larger clusters of 20 {Angstrom} to 30 {Angstrom} size were obtained by thermal annealing of the as grown material. X-ray diffraction and transmission electron microscopy confirm the high crystalline quality. A lattice contraction of 6.7% could be seen for 10 {Angstrom} sized GaAs clusters. The clusters are nearly spherical in shape. Optical absorption spectra show a distinct line which can be assigned to the fundamental transition of the quantum confined electronic state. The measured blue shift, with respect to the GaP bulk absorption edge is 0.53 eV. As the cluster is smaller than the exciton radius, we can calculate the cluster size from this blue shift and obtain 20.2 {Angstrom}, consistent with the results from X-ray diffraction of 19.5 {Angstrom} for the same sample.
Date: June 1, 1994
Creator: Laurich, B. K.; Smith, D. C. & Healy, M. D.
Partner: UNT Libraries Government Documents Department

Magnetic field dependence of up-converted photoluminescence in partially ordered GaInP{sub 2}/GaAs up to 23 T

Description: The influence of a strong magnetic field on the up-converted photoluminescence (PL) spectra of partially ordered layers of GaInP{sub 2} grown on GaAs substrate have been investigated. The up-converted PL spectra exhibit 2 peaks. The position of the low energy peak is close to that of the peak observed in Pl spectra excited by above GaInP{sub 2} bandgap light while the other peak occurs at about 30 meV higher in energy. Both peaks show a linear dependence on B between 0 and 23 T suggesting that free carriers with effective masses of 0.084 m{sub 0} and 0.24m{sub 0} (m{sub 0} is the free electron mass) are involved in these transitions. They interpret the low energy peak as originating from the recombination of localized holes with free electrons while the high energy peak is related to the recombination of localized electrons with free holes.
Date: September 1, 1996
Creator: Zeman, J.; Martinez, G.; Yu, P.Y. & Uchida, K.
Partner: UNT Libraries Government Documents Department

A polarization study of strained GaAs photocathode structures

Description: The polarized electron source at SLAC has performed extremely well during recent years supplying electrons having a spin polarization of 78% (85%) for high (low) current operation with beam current limited primarily by experimental requirements. However, there is room for improvement in the electron polarization. The less-than-ideal polarizations are a result of both imperfections and depolarizing mechanisms within the photocathode. The structure of the photocathode used at SLAC in the polarized electron source is a single-strained emitting layer structure grown atop a GaAs substrate. Here, the properties of several types of strained GaAs and GaAsP photocathodes have been studied using x-ray diffraction and photoemission.
Date: October 1, 1996
Creator: Mulhollan, G.; Garwin, E.L.; Maruyama, T.; Tang, H.; Mair, R. & Prepost, R.
Partner: UNT Libraries Government Documents Department

Effect of High-Voltage Heterojunction Bipolar Transistor Collector Design on f(T) and f(MAX)

Description: High-speed InGaP/GaAs heterojunction bipolar transistors (HBTs) for high-voltage circuit applications have been investigated. In order to obtain ideal IV characteristics, a lightly doped (N{sub DC} = 7.5 x 10{sup 15} cm{sup {minus}3}) thick (W{sub C} = 3.5 {micro}m) layer of GaAs was used as the collector layer. The devices fabricated have shown breakdown voltage exceeding 65 V. Device operated at up to a 60V bias, which is the highest operating voltage reported up to date for single heterojunction HBTs. Peak {line_integral}{sub T} and {line_integral}{sub MAX} values of 18 GHz and 29 GHz, respectively, have been achieved on a device with emitter area of 4x 12.5 {micro}m{sup 2}. Both {line_integral}{sub T} and {line_integral}{sub Max} degrades with higher bias, which is related to the elongation of the collector depletion width.
Date: March 2, 1999
Creator: Ashby, C.I.H.; Baca, A.G.; Chang, P.C. & Hietala, V.M.
Partner: UNT Libraries Government Documents Department

InAlGaP vertical cavity surface emitting lasers (VCSELs): Processing and performance

Description: (Al{sub y}Ga{sub 1{minus}y}){sup 1{minus}x}In{sub x}P semiconductor alloys lattice-matched to GaAs are widely used in visible optoelectronic devices. One of the most recent developments in this area is the AlGaInP-based red vertical cavity surface emitting laser (VCSEL). These lasers, which employ AlGaInP active regions and AlGaAs distributed Bragg reflectors (DBRs), have demonstrated continuous-wave (CW) lasing over the 630--690 nm region of the spectrum. Applications for these lasers include plastic fiber data communications, laser printing and bar code scanning. In this paper, the authors present an overview of recent developments in the processing and performance of AlGaInP based VCSELs. This overview will include a review of the general heterostructure designs that have been employed, as well as the performance of lasers fabricated by both ion implantation and selective oxidation.
Date: June 1, 1997
Creator: Crawford, M.H.; Choquette, K.D.; Hickman, R.J. & Geib, K.M.
Partner: UNT Libraries Government Documents Department

Comparison of experimental and theoretical gain-current relations in GaInP quantum well lasers

Description: The authors compare the results of a microscopic laser theory with gain and recombination currents obtained from experimental spontaneous emission spectra. The calculated absorption spectrum is first matched to that measured on a laser, ensuring that the quasi-Fermi levels for the calculation and the experiment (spontaneous emission and gain) are directly related. This allows one to determine the inhomogeneous broadening in their experimental samples. The only other inputs to the theory are literature values of the bulk material parameter. The authors then estimate the non-radiative recombination current associated with the well and wave-guide core from a comparison of measured and calculated recombination currents.
Date: January 10, 2000
Creator: Smowton, P.M.; Chow, W.W. & Blood, P.
Partner: UNT Libraries Government Documents Department

New approaches for high-efficiency solar cells. Final report

Description: This report summarizes the activities carried out in this subcontract. These activities cover, first the atomic layer epitaxy (ALE) growth of GaAs, AlGaAs and InGaP at fairly low growth temperatures. This was followed by using ALE to achieve high levels of doping both n-type and p-type required for tunnel junctions (Tj) in the cascade solar cell structures. Then the authors studied the properties of AlGaAs/InGaP and AlGaAs/GaAs tunnel junctions and their performances at different growth conditions. This is followed by the use of these tunnel junctions in stacked solar cell structures. The effect of these tunnel junctions on the performance of stacked solar cells was studied at different temperatures and different solar fluences. Finally, the authors studied the effect of different types of black surface fields (BSF), both p/n and n/p GaInP solar cell structures, and their potential for window layer applications. Parts of these activities were carried in close cooperation with Dr. Mike Timmons of the Research Triangle Institute.
Date: December 1, 1997
Creator: Bedair, S. M. & El-Masry, N. A.
Partner: UNT Libraries Government Documents Department

The unusual conduction band minimum formation of Ga(As{sub 0.5{minus}y}P{sub 0.5{minus}y}N{sub 2y}) alloys

Description: The conduction band minimum formation of GaAs{sub 0.5{minus}y}P{sub 0.5{minus}y}N{sub 2y} is investigated for small nitrogen compositions (0.1% &lt; 2y &lt; 1.0%), by using a pseudopotential technique. This formation is caused by two unusual processes both involving the deep-gap impurity level existing in the dilute alloy limit y {r_arrow} 0. The first process is an anticrossing with the {Gamma}{sub Ic}-like extended state of GaAs{sub 0.5}P{sub 0.5}. The second process is an interaction with other impurity levels forming a subband. These two processes are expected to occur in any alloys exhibiting a deep-gap impurity level at one of its dilute limit.
Date: May 11, 2000
Partner: UNT Libraries Government Documents Department

CuPt-type ordering of MOCVD In{sub 0.49}Al{sub 0.51}P.

Description: CuPt-type ordering in In{sub 0.49}Al{sub 0.51}P is studied by TEM. The lattice-matched film was grown by MOCVD on a GaAs substrate oriented 10{sup o} off (001) towards [110], at 650 C and 25 nm/min. TEM [110] and [1{bar 1}0] cross-sections (XS) were made by wedge polishing and 2 kV Ar ion milling. In CuPt-type ordering of In{sub 0.52}Ga{sub 0.48}P, alternating In-Ga-In-Ga {l_brace}111{r_brace} planes of group III atoms produce 1/2 {bar 1}11 and 1/2 1{bar 1}1 order spots in the 110 SADP, while the [1{bar 1}0] SADP shows no order spots [1-3]. A few studies have reported this type of order in In{sub 0.49}Al{sub 0.51}P [4]. The 004 BF image of the [1{bar 1}0] XS in Fig. 1 shows uneven light/dark contrast modulation due to phase separation often observed in In{sub 0.52}Ga{sub 0.48}P. There are also light/dark layers marked ML parallel to the film growth plane; such unintentional multilayers have also been observed [5] but their origin is not understood. Order lamellae {approx}1.5 nm thick inclined at a shallow angle to the growth plane overlap the multilayer to produce Moire fringe contrast. Fig. 2 is a DF image showing the thin ordered domains in the [1{bar 1}0] XS, which are inclined at 12{sup o} to the growth plane and 2{sup o} to (001). Fig. 3a shows the absence of order spots in the [1{bar 1}0] SADP, while tilting 26.6{sup o} to [3{bar 1}0] reveals rows of order spots characteristic of CuPt ordering (Fig. 3b). The fact that the domains lie within {approx}2{sup o} of (001) shows that their orientation is crystallographically determined, while the fact that the ''multilayer'' is parallel to the growth plane rather than to (001) shows that it is not crystallographically determined. Most work does not describe domains in the [1{bar 1}0] XS, but Bellon et al. [1] ...
Date: March 14, 2002
Creator: Kosel, T. H.; Hall, D. C.; Dupuis, R. D.; Heller, R. D. & Cook, R. E.
Partner: UNT Libraries Government Documents Department

Characterization of Zns-GaP Naon-composites

Description: It proved possible to produce consistent, high-quality nanocrystalline ZnS powders with grain sizes as small as 8 nm. These powders are nano-porous and are readily impregnated with GaP precursor, although inconsistently. Both crystal structure and small grain size of the ZnS can be maintained through the use of GaP. Heat treatment of the impregnated powders results in a ZnS-GaP composite structure where the grain sizes of the phases are on the order of 10--20 nm. Conventional powder processing should be able to produce optically dense ceramic compacts with improved mechanical properties and suitable IR transmission.
Date: December 9, 1993
Creator: Todd, V.
Partner: UNT Libraries Government Documents Department

Enhancement of Spin-Polarized Electron Emission from Strain-Compensated AlInGaAs-GaAsP Superlattices

Description: Resonance enhancement of the quantum efficiency of new polarized electron photocathodes based on a short-period strain-compensated AlInGaAs/GaAsP superlattice structure is reported. The superlattice is a part of an integrated Fabry-Perot optical cavity. We demonstrate that the Fabry-Perot resonator enhances the quantum efficiency by up to a factor 10 in the wavelength region of the main polarization maximum. The high structural quality implied by these results points to the very promising application of these photocathodes for spin-polarized electron sources.
Date: December 8, 2006
Creator: Roberts, J.S.; U., /Sheffield; Yashin, Yu.P.; Mamaev, Yu.A.; Gerchikov, L.G.; Inst., /St. Petersburg Polytechnic et al.
Partner: UNT Libraries Government Documents Department

Polarization Possibilities of Small Spin-Orbit Interaction in Strained-Superlattice Photocathodes

Description: Strained-superlattice photocathodes based on InGaP/GaAs were investigated. The photocathode performance is found highly dependent on the superlattice parameters. The electron confinement energy in superlattice appears important.
Date: December 12, 2006
Creator: Maruyama, T.; Brachmann, A.; Clendenin, J.E.; Garwin, E.L.; Ioakeimidi, K.; Kirby, R.E. et al.
Partner: UNT Libraries Government Documents Department

Polarization Possibilities of Small Spin-Orbit Interaction in Strained-Superlattice Photocathodes

Description: Strained-superlattice photocathodes based on InGaP/GaAs were investigated. The photocathode performance is found highly dependent on the superlattice parameters. The electron confinement energy in superlattice appears important. The strained-superlattice structure based on GaAsP/GaAs, with a maximum polarization as high as 90% and more than 1% quantum efficiency, is presently the prime candidate for the ILC polarized electron photocathodes. A recent systematic study shows, however, that the peak polarization seems saturated even though the heavy-hole (HH) and light-hole (LH) band splitting is increased significantly, indicating that there is a material specific spin relaxation mechanism. It is widely accepted that the D'yakonov-Perel mechanism is the dominant spin relaxation mechanism in the III-V compound superlattice structures with a low p-doping ({le} 10{sup 17} cm{sup -3}), and that the spin relaxation may be reduced by choosing a material with a smaller spin-orbit interaction. As the spin-orbit interaction in phosphides is much smaller than in arsenides, strained-superlattice structure based on InGaP/GaAs were investigated. The computer code SPECCODE developed by Subashiev and Gerchikov has been used for calculating the band structures in superlattice.
Date: August 25, 2010
Partner: UNT Libraries Government Documents Department

Ion implantation for high performance III-V JFETS and HFETS

Description: Ion implantation has been an enabling technology for realizing many high performance electronic devices in III-V semiconductor materials. We report on advances in ion implantation processing for GaAs JFETs (joint field effect transistors), AlGaAs/GaAs HFETs (heterostructure field effect transistors), and InGaP or InAlP-barrier HFETs. The GaAs JFET has required the development of shallow p-type implants using Zn or Cd with junction depths down to 35 nm after the activation anneal. Implant activation and ionization issues for AlGaAs are reported along with those for InGaP and InAlP. A comprehensive treatment of Si-implant doping of AlGaAs is given based on donor ionization energies and conduction band density-of-states dependence on Al-composition. Si and Si+P implants in InGaP are shown to achieve higher electron concentrations than for similar implants in AlGaAs due to absence of the deep donor level. An optimized P co- implantation scheme in InGaP is shown to increase the implanted donor saturation level by 65%.
Date: June 1, 1996
Creator: Zolper, J.C.; Baca, A.G.; Sherwin, M.E. & Klem, J.F.
Partner: UNT Libraries Government Documents Department

Effect of Inert Gas Additive Species on Cl(2) High Density Plasma Etching of Compound Semiconductors: Part II. InP, InSb, InGaP and InGaAs

Description: The effects of the additive noble gases He, Ar and Xe on chlorine-based Inductively Coupled Plasma etching of InP, InSb, InGaP and InGaAs were studied as a function of source power, chuck power and discharge composition. The etch rates of all materials with C12/He and C12/Xe are greater than with C12/Ar. Etch rates in excess of 4.8 pndmin for InP and InSb with C12/He or C12/Xe, 0.9 pndmin for InGaP with C12/Xe, and 3.8 prdmin for InGaAs with Clz/Xe were obtained at 750 W ICP power, 250 W rf power, - 1570 C12 and 5 mTorr. All three plasma chemistries produced smooth morphologies for the etched InGaP surfaces, while the etched surface of InP showed rough morphology under all conditions.
Date: December 17, 1998
Creator: Abernathy, C.R.; Cho, H.; Hahn, Y.B.; Hays, D.C.; Jung, K.B.; Pearton, S.J. et al.
Partner: UNT Libraries Government Documents Department

ECR etching of GaP, GaAs, InP, and InGaAs in Cl{sub 2}/Ar, Cl{sub 2}/N{sub 2}, BCl{sub 3}/Ar, and BCl{sub 3}/N{sub 2}

Description: Electron cyclotron resonance (ECR) etching GaP, GaAs, InP, and InGaAs are reported as a function of percent chlorine-containing gas for Cl{sub 2}/Ar, Cl{sub 2}/N{sub 2}, BCl{sub 3}/Ar, and BCl{sub 3}N{sub 2} plasma chemistries. GaAs and GaP etch rates were faster than InP and InGaAs, independent of plasma chemistry due to the low volatility of the InCl{sub x} etch products. GaAs and GaP etch rates increased as %Cl{sub 2} was increased for Cl{sub 2}/Ar and Cl{sub 2}/N{sub 2} plasmas. The GaAs and GaP etch rates were much slower in BCl{sub 3}-based plasmas due to lower concentrations of reactive Cl, however enhanced etch rates were observed in BCl{sub 3}/N{sub 2} at 75% BCl{sub 3}. Smooth etched surfaces were obtained over a wide range of plasma chemistries.
Date: June 1, 1996
Creator: Shul, R.J.; Baca, A.G.; Rieger, D.J.; Hou, H.; Pearton, S.J. & Ren, F.
Partner: UNT Libraries Government Documents Department

Short-range order types in binary alloys: A reflection of coherent phase stability

Description: The short-range order (SRO) present in disordered solid solutions is classified according to three characteristic system-dependent energies: (1) formation enthalpies of ordered compounds, (2) enthalpies of mixing of disordered alloys, and (3) the energy of coherent phase separation, (the composition-weighted energy of the constituents each constrained to maintain a common lattice constant along an A/B interface). These energies are all compared against a common reference, the energy of incoherent phase separation (the composition-weighted energy of the constituents each at their own equilibrium volumes). Unlike long-range order (LRO), short-range order is determined by energetic competition between phases at a fixed composition, and hence only coherent phase-separated states are of relevance for SRO. The authors find five distinct SRO types, and show examples of each of these five types, including Cu-Au, Al-Mg, GaP-InP, Ni-Au, and Cu-Ag. The SRO is calculated from first-principles using the mixed-space cluster expansion approach combined with Monte Carlo simulations. Additionally, they examine the effect of inclusion of coherency strain in the calculation of SRO, and specifically examine the appropriate functional form for accurate SRO calculations.
Date: November 23, 1999
Creator: Wolverton, W.; Ozolins, V. & Zunger, Alex
Partner: UNT Libraries Government Documents Department

Magnetoluminescence studies in ordered InGaP{sub 2}

Description: Photouminescence measurements on ordered InGap{sub 2} were studied as a function of temperature, laser power density, and magnetic field. The temperature varied between 1.4 and 300 K, the laser power densities ranged from 10 nW/cm{sup 2} to 20 W/cm{sup 2}, and the maximum magnetic field was 13.6 T. The data show both excitonic and band-to-band behavior, depending upon the incident laser power density. A consistent interpretation of all data leads to a type-II valence-band offset between the ordered domains. Finally, a charge transfer model between domains which provides an explanation for intensity dependent energy shifts is discussed.
Date: December 1, 1995
Creator: Jones, E.D.; Schneider, R.P. Jr. & Mascarenhas, A.
Partner: UNT Libraries Government Documents Department

High-Power Reliable Operation of InGaAsP/InP Laser Bars at 1.73 {micro}m

Description: InGaAsP/InP laser bars with an emission wavelength of 1.73 {micro}m have been fabricated using compressively-strained multiple-quantum-well separate-confinement heterostructures. One-cm-wide, 0.7-fill-factor, diode bars are bonded onto Si microchannel heatsinks. A maximum cw power of 16 W was produced from a one-cm bar. Derated to SW cw, the extrapolated lifetime is 10,000 hours of operation with a 20% degradation in output power. A 10-bar microlensed diode array with a one-square-cm aperture produced 200 W of peak power and was focused onto a Cr:ZnSe slab laser. Over 3 watts of pulsed power and xxmw of average power was generated at a wavelength of 2.5 {micro}m.
Date: February 16, 1999
Creator: Skidmore, J.; Page, R.H.; Freitas, B.L.; Reinhardt, C.E.; Utterback, E.J. & Emanuel, M.A.
Partner: UNT Libraries Government Documents Department

Study of the chemistry of the (111) GaP planes by atom-probe field-ion microscopy. Report No. 4256

Description: Atom-probe field-ion microscope (FIM) analyses were performed on specimens of the compound semiconductor GaP. Purposes were to show the step-like field-evaporation behavior - corresponding to each atomic layer of the (111) planes - and to determine the chemistry of each plane of atoms. These types of information are of great potential value for the study of a wide range of physical problems involving compound semiconductors. The studies showed that the chemistry of each (111) plane could indeed be determined and that small deviations from stoichiometry within a given plane were also measurable. The overall stoichiometry of GaP was found to be related to the background gas hydrogen and the number of ions field-evaporated per pulse. The observations were explained in terms of possible field-evaporation mechanisms involving the main background gas in the FIM - hydrogen.
Date: May 1, 1980
Creator: Yamamoto, M.; Seidman, D. N. & Nakamura, S.
Partner: UNT Libraries Government Documents Department