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11 Jan 1999

Volume 74, Issue 2, pp. 161-325

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Zeeman splitting of shallow donors in GaN

Francisco Mireles and Sergio E. Ulloa

Appl. Phys. Lett. 74, 248 (1999); http://dx.doi.org/10.1063/1.123270 (3 pages) | Cited 13 times

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The Zeeman splitting of the donor spectra in cubic and hexagonal GaN is studied using an effective mass theory approach. Soft-core pseudopotentials were used to describe the chemical shift of the different substitutional dopants. The donor ground states calculated range from 29.5 to 33.7 meV, with typically 1 meV higher binding in the hexagonal phase. Carbon is found to produce the largest donor binding energy. The ionization levels and excited states are in excellent agreement with Hall and optical measurements, and suggest the presence of residual C in recent experiments. © 1999 American Institute of Physics.
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71.55.Eq III-V semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
78.20.Ls Magneto-optical effects
77.22.Ch Permittivity (dielectric function)

Negative capacitance in forward biased hydrogenated amorphous silicon p+-i-n+ diodes

F. Lemmi and N. M. Johnson

Appl. Phys. Lett. 74, 251 (1999); http://dx.doi.org/10.1063/1.123271 (3 pages) | Cited 26 times

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We present experimental results and a physical explanation for the negative values of the small-signal capacitance of forward biased hydrogenated amorphous silicon (a-Si:H) p+-i-n+ diodes. The device capacitance varies with the probe signal frequency. In the low frequency range the measured capacitance shows large negative values if the diode is sufficiently forward biased. Higher forward bias voltages shift this effect to higher frequencies. Time domain response of the device to a small voltage step and a Fourier transform of the resulting transient current provide a verification of the results. The time domain data also suggest the physical mechanism responsible for the overall dispersive behavior: separate and delayed trapping processes for holes and electrons at the interfaces with the two doped layers. © 1999 American Institute of Physics.
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85.30.Kk Junction diodes
85.60.Dw Photodiodes; phototransistors; photoresistors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Enhancement of the quantum-confined stark effect utilizing asymmetric quantum well structures

R. K. Gug and W. E. Hagston

Appl. Phys. Lett. 74, 254 (1999); http://dx.doi.org/10.1063/1.123272 (3 pages) | Cited 5 times

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The potential profile of a rectangular quantum well is optimized so as to maximize the quantum confined stark effect. Digitization of this profile gives a structure which can be grown experimentally. As an example, a well of width 100 Å in Al0.4Ga0.6As/GaAs is optimized giving a structure which is both asymmetric and double quantum well like. The associated redshift is increased at large fields by a factor of more than 4 compared with the original structure, and the associated oscillator strengths are a much more sensitive function of the applied field. This example illustrates the utility of such optimized structures for device applications. © 1999 American Institute of Physics.
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78.20.Jq Electro-optical effects
78.66.Fd III-V semiconductors

Evidence of discrete interface traps on thermally grown thin silicon oxide films

Jin Cai and Chih-Tang Sah

Appl. Phys. Lett. 74, 257 (1999); http://dx.doi.org/10.1063/1.123273 (3 pages) | Cited 5 times

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A very-low density (<1010 cm−2) residual discrete energy-level interface trap at 228 meV from the Si midgap is detected on crystalline silicon covered by thermally grown oxide. Three signatures pointing to discreteness are delineated in the experimental data of the gate voltage modulation of the dc steady-state electron-hole recombination rate. Using the Shockley-Read–Hall recombination kinetics, the energy level is shown to have a linewidth less than 20 meV. From the present and previous data, the dopant impurity origin of this residual interface trap species is speculated rather than the amphoteric silicon dangling bonds. © 1999 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Ng Insulators
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Modeling of the temperature dependence of the field-effect mobility in thin film devices of conjugated oligomers

J. H. Schön and B. Batlogg

Appl. Phys. Lett. 74, 260 (1999); http://dx.doi.org/10.1063/1.123274 (3 pages) | Cited 31 times

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A simple model is proposed for charge carrier transport across grain boundaries with an acceptor-like trap level. Potential wells between the grains are formed due to negatively charged grain boundaries. Based on this model, a variety of temperature dependencies of the charge carrier mobility can be described. Using realistic parameters, this model reproduces very well the measured temperature dependencies of the field-effect mobility in polycrystalline pentacene and oligothiophene thin film devices. Therefore, it seems to be difficult to investigate the intrinsic material properties of organic semiconductors using only polycrystalline field-effect devices, since they may be masked by the effects of traps and grain boundaries. © 1999 American Institute of Physics.
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85.30.Tv Field effect devices
73.50.Dn Low-field transport and mobility; piezoresistance
61.72.Mm Grain and twin boundaries
73.61.Ph Polymers; organic compounds
85.30.De Semiconductor-device characterization, design, and modeling

Exciton localization and the Stokes’ shift in InGaN epilayers

R. W. Martin, P. G. Middleton, K. P. O’Donnell, and W. Van der Stricht

Appl. Phys. Lett. 74, 263 (1999); http://dx.doi.org/10.1063/1.123275 (3 pages) | Cited 111 times

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We report a comparative study of the emission and absorption spectra of a range of commercial InGaN light-emitting diodes and high-quality epilayers. A working definition of the form of the absorption edge for alloys is proposed, which allows a unique definition of the Stokes’ shift. A linear dependence of the Stokes’ shift on the emission peak energy is then demonstrated for InGaN using experimental spectra of both diode and epilayer samples, supplemented by data from the literature. In addition, the broadening of the absorption edge is shown to increase as the emission peak energy decreases. These results are discussed in terms of the localization of excitons at highly indium-rich quantum dots within a phase-segregated alloy. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
85.60.Jb Light-emitting devices
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.40.Fy Semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.60.Fi Electroluminescence

Threshold photoemission analysis of the surface reactions of triethylgallium and trimethylgallium on GaAs(100): A promising technique for kinetics studies

N. Viguier and F. Maury

Appl. Phys. Lett. 74, 266 (1999); http://dx.doi.org/10.1063/1.123276 (3 pages) | Cited 2 times

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The decomposition of triethylgallium and trimethylgallium on a As-stabilized GaAs(100) surface has been analyzed by near threshold photoemission. For T ⩽ 200 °C, the negative photocurrent change induced by adsorption of these electron acceptor molecules is directly related to the coverage. The adsorbed diethylgallium species decompose very rapidly above 240 °C to adsorbed Ga atoms, resulting in a positive photocurrent change due to the lower work function of a Ga surface. The activation energy and preexponential factor of this decomposition reaction were derived independently in the temperature range 200–240 °C from the time dependence of the photocurrent emitted from the surface upon exposure to triethylgallium at saturated coverage. © 1999 American Institute of Physics.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
79.60.Dp Adsorbed layers and thin films
68.08.-p Liquid-solid interfaces
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
82.20.Pm Rate constants, reaction cross sections, and activation energies

Germanium “quantum dots” embedded in silicon: Quantitative study of self-alignment and coarsening

O. Kienzle, F. Ernst, M. Rühle, O. G. Schmidt, and K. Eberl

Appl. Phys. Lett. 74, 269 (1999); http://dx.doi.org/10.1063/1.123277 (3 pages) | Cited 59 times

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We report on experiments aiming to produce Ge quantum dots embedded in Si. Employing cross-sectional transmission electron microscopy, we have studied the misfit stress-induced self-alignment of islands belonging to consecutive Stranski–Krastanov layers of Ge buried in Si by molecular beam epitaxy. Quantitative evaluation of the micrographs has revealed the critical Si interlayer thickness below which the island positions in successive Ge layers begin to correlate. Moreover, we have quantitatively analyzed the influence of the Si interlayer thickness on the coarsening of the Ge islands from one buried Ge layer to the next. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.05.Cy Elemental semiconductors
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
68.55.-a Thin film structure and morphology

Quantification of scanning capacitance microscopy imaging of the pn junction through electrical simulation

M. L. O’Malley, G. L. Timp, S. V. Moccio, J. P. Garno, and R. N. Kleiman

Appl. Phys. Lett. 74, 272 (1999); http://dx.doi.org/10.1063/1.123278 (3 pages) | Cited 38 times

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Determining the cross-sectional doping profile of very small metal–oxide–semiconductor field effect transistors and specifically the direct measurement of their channel length is necessary for true channel engineering to be possible. Scanning capacitance microscopy (SCM) has generated unprecedented images of the cross-sectional doping profiles of very small transistors. The bias voltage dependence of these images has motivated us to investigate the SCM technique in greater detail. Using electrical simulations, we have focused on the pn junction to establish the qualitative and quantitative relationship between the bias voltage and the pn junction location. The ability to confidently interpret the images produced with SCM will allow us to improve simulation models, trouble-shoot process flow, and determine the effective channel length of semiconductor devices. © 1999 American Institute of Physics.  
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85.30.Tv Field effect devices
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
85.30.De Semiconductor-device characterization, design, and modeling
61.72.S- Impurities in crystals

Low-resistance Ta/Ti Ohmic contacts for p-type GaN

Masaaki Suzuki, T. Kawakami, T. Arai, S. Kobayashi, Yasuo Koide, T. Uemura, N. Shibata, and Masanori Murakami

Appl. Phys. Lett. 74, 275 (1999); http://dx.doi.org/10.1063/1.123279 (3 pages) | Cited 45 times

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Although extensive efforts have continued to develop Ohmic contacts for p-type GaN, which have specific contact resistance (ρc) lower than that (ρc ∼ 10−2 Ω cm2) of conventional Ni/Au contacts, to the best of our knowledge no breakthrough has been reported in open literature. We demonstrated that bilayered Ta/Ti contacts have a ρc value of around 3×10−5 Ω cm2 for p-type GaN with a hole concentration of 7×1017 cm−3. This contact has resistance low enough to manufacture blue laser diodes, but deterioration of the ρc value during room-temperature storage is the key issue. © 1999 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
42.55.Px Semiconductor lasers; laser diodes

Detection of copper contamination in silicon by surface photovoltage diffusion length measurements

Worth B. Henley, Deepak A. Ramappa, and Lubek Jastrezbski

Appl. Phys. Lett. 74, 278 (1999); http://dx.doi.org/10.1063/1.123280 (3 pages) | Cited 26 times

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Surface photovoltage minority carrier lifetime/diffusion length analysis of copper contaminated silicon was performed. It was observed that copper and copper associated defects degrade minority carrier lifetime more in n-type than in p-type silicon. This finding is explained by analysis of copper related defect levels identified by other deep level transient spectroscopy studies. In copper contaminated p-type silicon, an optical or thermal activation procedure significantly degrades the diffusion length. A process similar to that of Fe–B in p-type silicon is proposed. The activation process dissociates the Cu–Cu pairs, a weak recombination center in p-type silicon, and the copper forms extended substitutional defects in silicon, which have much greater recombination activity. No recovery of diffusion length was observed following such an activation procedure. The difference in copper and iron diffusion length recovery properties after activation can be used to differentiate iron contamination from copper contamination. © 1999 American Institute of Physics.
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71.55.Cn Elemental semiconductors
72.40.+w Photoconduction and photovoltaic effects
73.25.+i Surface conductivity and carrier phenomena
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors
61.72.S- Impurities in crystals

Local coordination of Ga impurity in hydrogenated amorphous germanium studied by extended x-ray absorption fine-structure spectroscopy

G. Dalba, P. Fornasini, R. Grisenti, F. Rocca, D. Comedi, and I. Chambouleyron

Appl. Phys. Lett. 74, 281 (1999); http://dx.doi.org/10.1063/1.122999 (3 pages) | Cited 5 times

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The local structure of Ga-doped a-Ge:H films has been investigated by extended x-ray absorption fine-structure (EXAFS) fluorescence for impurity concentrations ranging from 1.5×1018 atoms cm−3 to 4.5×1020 atoms cm−3. The mean-coordination number of Ga atoms changes from around 4 (1.5×1018–1.5×1019 cm−3) to below 3 (1.5×1020–4.5×1020 cm−3) with rising concentration. The change from fourfold to threefold coordination occurs in a rather narrow impurity concentration range. The variance of the distance distribution function decreases with increasing Ga content, suggesting that well-ordered sites are present at high-impurity concentration. From EXAFS phase analysis the first Ga–Ge shell distance has been found to be 0.03 Å larger in the amorphous network than in Ga-doped crystalline Ge. © 1999 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.43.Dq Amorphous semiconductors, metals, and alloys
78.70.Dm X-ray absorption spectra

Majority- and minority-carrier traps in Te-doped AlInP

Y. R. Wu, W. J. Sung, and W. I. Lee

Appl. Phys. Lett. 74, 284 (1999); http://dx.doi.org/10.1063/1.123000 (3 pages) | Cited 2 times

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The properties of deep levels found in Te-doped AlInP grown by metal–organic chemical vapor deposition have been studied. By using pn-junction structure, both minority- and majority-carrier traps can be observed. Two deep levels are found in Te-doped AlInP: one majority-carrier trap and one minority-carrier trap. The activation energies of majority- and minority-carrier traps are 0.24±0.05 and 0.25±0.03 eV, respectively. The majority-carrier trap is uniformly distributed, indicating that this level belongs to some kind of bulk defect. © 1999 American Institute of Physics.
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71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Electron mobility in modulation-doped AlGaN–GaN heterostructures

R. Gaska, M. S. Shur, A. D. Bykhovski, A. O. Orlov, and G. L. Snider

Appl. Phys. Lett. 74, 287 (1999); http://dx.doi.org/10.1063/1.123001 (3 pages) | Cited 70 times

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We report on the measurements of the electron mobility in modulation-doped Al0.2Ga0.8N–GaN heterostructures grown on sapphire, conducting 6H–SiC, and insulating 4H–SiC substrates as a function of the sheet electron density, ns, at the heterointerface in a wide temperature range. The mobility increases with an increase in ns up to approximately 1×1013 cm−2 and decreases with a further increase in ns. This is explained by the electron spillover at high values of ns from the two-dimensional states at the AlGaN/GaN heterointerface into the delocalized states in the doped GaN channel. The maximum electron Hall mobility in excess of 2000 cm2/V s at room temperature and 11 000 cm2/V s at 4.2 K was measured in the heterostructures grown on 6H–SiC at the values of ns close to 1013 cm−2 and 7×1012 cm−2, respectively. © 1999 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.20.At Surface states, band structure, electron density of states
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