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20 Jan 2003

Volume 82, Issue 3, pp. 313-483

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 370 (2003); http://dx.doi.org/10.1063/1.1537514 (3 pages)

Jan Schroers, Chris Veazey, and William L. Johnson
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Temperature dependence of free-exciton luminescence in cubic CdS films

Yoshihiko Kanemitsu, Takehiko Nagai, Yoichi Yamada, and Tsunemasa Taguchi

Appl. Phys. Lett. 82, 388 (2003); http://dx.doi.org/10.1063/1.1537436 (3 pages) | Cited 11 times

Online Publication Date: 15 January 2003

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Free-exciton photoluminescence (PL) properties of cubic CdS films on GaAs substrates have been studied by means of picosecond time-resolved PL spectrum measurements. A PL band appears at the light-hole exciton energy in strained CdS films. The linewidth of the free-exciton PL is determined by the inhomogeneous strains and the exciton–phonon interactions. At high temperatures above 80 K, the linewidth of the exciton luminescence drastically increases and the exciton-optical-phonon interaction is the dominant scattering process. The temperature dependence of free-exciton luminescence has been determined for cubic CdS films. © 2003 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
71.35.Gg Exciton-mediated interactions
78.47.-p Spectroscopy of solid state dynamics
68.60.Bs Mechanical and acoustical properties

Thermally stable Ir Schottky contact on AlGaN/GaN heterostructure

Chang Min Jeon, Ho Won Jang, and Jong-Lam Lee

Appl. Phys. Lett. 82, 391 (2003); http://dx.doi.org/10.1063/1.1536246 (3 pages) | Cited 24 times

Online Publication Date: 15 January 2003

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We report thermally stable Ir Schottky contacts on AlGaN/GaN heterostructure. The Schottky barrier height was increased from 0.68 to 1.07 eV, and the reverse leakage current dramatically decreased after annealing at 500 °C under O2 ambient. No degradation in Schottky barrier height was observed after annealing at 500 °C for 24 h. The oxidation annealing caused predominant Ga outdiffusion to the surface, leading to the shift of surface Fermi level to the energy level of Ga vacancy. This played a role in forming the Schottky contact with large barrier height and excellent thermal stability. © 2003 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
68.35.Fx Diffusion; interface formation
68.60.Dv Thermal stability; thermal effects
73.20.At Surface states, band structure, electron density of states

Microelectromechanical displacement sensing using InAs/AlGaSb heterostructures

Hiroshi Yamaguchi, Sen Miyashita, and Yoshiro Hirayama

Appl. Phys. Lett. 82, 394 (2003); http://dx.doi.org/10.1063/1.1537047 (3 pages) | Cited 10 times

Online Publication Date: 15 January 2003

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We fabricated self-sensing microelectromechanical displacement sensors from InAs/AlGaSb heterostructures. The sensitivity increased with reduced InAs thickness showing that the piezoresistivity was strongly enhanced when the quantum level approached to the pinning position of surface Fermi level. The high-sensitivity allowed us to detect a subangstrom displacement induced by thermal vibration of cantilevers. © 2003 American Institute of Physics.
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07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states

Charging effects in silicon nanocrystals within SiO2 layers, fabricated by chemical vapor deposition, oxidation, and annealing

D. N. Kouvatsos, V. Ioannou-Sougleridis, and A. G. Nassiopoulou

Appl. Phys. Lett. 82, 397 (2003); http://dx.doi.org/10.1063/1.1537869 (3 pages) | Cited 63 times

Online Publication Date: 15 January 2003

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Metal–insulator–semiconductor structures with a layer of silicon nanocrystals embedded within the SiO2 layer at a tunneling distance from a p-type silicon substrate and fabricated using chemical vapor deposition, oxidation, and annealing, exhibited charge trapping, determined from the capacitance–voltage (C–V) characteristics, which abruptly increased at fields above 2.5 MV/cm. Electrons or holes are trapped when biasing the structure into inversion or accumulation, respectively, and retention of trapped charge is demonstrated. The I–V characteristics exhibit an N-shaped form, indicating screening effects due to charging; an initial current spike, attributed to transient charging of nanocrystals, occurs at the same voltage causing abrupt C–V shift increase, with Fowler–Nordheim current rising at higher voltages. These structures are promising for memory device applications. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Gk Tunneling
81.16.Pr Micro- and nano-oxidation
61.46.-w Structure of nanoscale materials
81.05.Cy Elemental semiconductors
73.63.Bd Nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Gold Schottky contacts on oxygen plasma-treated, n-type ZnO(000math)

B. J. Coppa, R. F. Davis, and R. J. Nemanich

Appl. Phys. Lett. 82, 400 (2003); http://dx.doi.org/10.1063/1.1536264 (3 pages) | Cited 140 times

Online Publication Date: 15 January 2003

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Reverse bias current–voltage measurements of ∼100-μm-diameter gold Schottky contacts deposited on as-received, n-type ZnO(000math) wafers and those exposed for 30 min to a remote 20% O2/80% He plasma at 525±20 °C and cooled either in vacuum from 425 °C or the unignited plasma gas have been determined. Plasma cleaning resulted in highly ordered, stoichiometric, and smooth surfaces. Contacts on as-received material showed μA leakage currents and ideality factors >2. Contacts on plasma-cleaned wafers cooled in vacuum showed ∼ 36±1 nA leakage current to −4 V, a barrier height of 0.67±0.05 eV, and an ideality factor of 1.86±0.05. Cooling in the unignited plasma gas coupled with a 30 s exposure to the plasma at room temperature resulted in decreases in these parameters to ∼20 pA to −7 V, 0.60±0.05 eV, and 1.03±0.05, respectively. Differences in the measured and theoretical barrier heights indicate interface states. (0001) and (000math) are used in this letter to designate the polar zinc- and oxygen-terminated surfaces, respectively. © 2003 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.-r Electron states at surfaces and interfaces
81.05.Dz II-VI semiconductors

Electrical field effect of H-implantation induced defect states in GaN

A. Krtschil, A. Kielburg, H. Witte, A. Krost, J. Christen, A. Wenzel, and B. Rauschenbach

Appl. Phys. Lett. 82, 403 (2003); http://dx.doi.org/10.1063/1.1539281 (3 pages) | Cited 1 time

Online Publication Date: 15 January 2003

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Gallium nitride layers grown by metalorganic vapor phase epitaxy on sapphire substrates were implanted with 20 keV hydrogen ions with fluences between 2×1014 and 2×1015 ions per cm2. The resulting deep level spectrum was analyzed by deep level transient as well as by admittance spectroscopy. Beside several electron traps of probably intrinsic nature already known from other implantation experiments, a group of defects exclusively appeared after hydrogen implantation showing a strong electrical field effect in the corresponding emission characteristics. These peculiar states were characterized in detail and compared with defects showing a similar field effect already observed by other groups, suggesting the interpretation as hydrogen-decorated dislocations. © 2003 American Institute of Physics.
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71.55.Eq III-V semiconductors
61.80.Jh Ion radiation effects
61.72.uj III-V and II-VI semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect
61.82.Fk Semiconductors

Charge carrier mobility in an organic-inorganic hybrid nanocomposite

Kaushik Roy Choudhury, Jeffrey G. Winiarz, Marek Samoc, and Paras N. Prasad

Appl. Phys. Lett. 82, 406 (2003); http://dx.doi.org/10.1063/1.1537054 (3 pages) | Cited 18 times

Online Publication Date: 15 January 2003

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Organic-inorganic hybrid materials are media for electronic and optoelectronic applications. We present a study of the electronic transport in such a model nanoparticle-sensitized hybrid organic-inorganic photorefractive host system, consisting of poly(N-vinylcarbazole) doped with quantum dots of cadmium sulfide, using standard time-of-flight techniques. The photocurrent transients exhibit features typical of dispersive transport in an amorphous semiconductor. The hole mobility depends strongly on the electric field and temperature indicating Poole–Frenkel-like activated hopping transport; a thickness dependence of the mobility is observed. The presence of nanoparticles does not lead to increased trapping of holes. Conversely, a surprising result is observed: the mobility actually increases with the increase of nanoparticle concentration even though it is well below the percolation limit. © 2003 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Tm Composite materials
81.07.Pr Organic-inorganic hybrid nanostructures
72.40.+w Photoconduction and photovoltaic effects
73.63.Kv Quantum dots
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
72.20.Ee Mobility edges; hopping transport

Coherent control of nuclear-spin system in a quantum-Hall device

Tomoki Machida, Tomoyuki Yamazaki, Kenji Ikushima, and Susumu Komiyama

Appl. Phys. Lett. 82, 409 (2003); http://dx.doi.org/10.1063/1.1539903 (3 pages) | Cited 52 times

Online Publication Date: 15 January 2003

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Coherent control of local nuclear spins in a solid-state device is demonstrated. By unequally populating spin-resolved quantum-Hall edge channels, nuclear spins in a limited region along the edge channels are strongly polarized via the hyperfine interaction. Pulsed rf magnetic fields, generated by a built-in micrometal strip, cause the nuclear-spin state to evolve coherently. The nuclear-spin state reached during the pulse duration is finally read out via the edge-channel conductance, which shows Rabi oscillation. © 2003 American Institute of Physics.
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73.43.Nq Quantum phase transitions
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.70.Jp Nuclear states and interactions
76.60.-k Nuclear magnetic resonance and relaxation

Mobility enhancement in strained Si modulation-doped structures by chemical mechanical polishing

K. Sawano, S. Koh, Y. Shiraki, Y. Hirose, T. Hattori, and K. Nakagawa

Appl. Phys. Lett. 82, 412 (2003); http://dx.doi.org/10.1063/1.1539557 (3 pages) | Cited 18 times

Online Publication Date: 15 January 2003

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The strained Si modulation-doped (MOD) structure formed on the strain-relaxed SiGe buffer layer planarized by chemical mechanical polishing (CMP) was found to show significant mobility enhancement. The enhancement reaches a factor of 6 at low temperatures. The backgate dependence as well as temperature dependence of the transport properties of the MOD structure were investigated, and it was suggested that CMP drastically reduced the roughness scattering and increased the mobility of two-dimensional electron gas in the strained Si. © 2003 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Ee Mobility edges; hopping transport
81.65.Ps Polishing, grinding, surface finishing
72.20.Fr Low-field transport and mobility; piezoresistance
73.25.+i Surface conductivity and carrier phenomena
68.35.B- Structure of clean surfaces (and surface reconstruction)

Mechanism for thermoelectric figure-of-merit enhancement in regimented quantum dot superlattices

Alexander A. Balandin and Olga L. Lazarenkova

Appl. Phys. Lett. 82, 415 (2003); http://dx.doi.org/10.1063/1.1539905 (3 pages) | Cited 51 times

Online Publication Date: 15 January 2003

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We propose a mechanism for enhancement of the thermoelectric figure-of-merit in regimented quantum dot superlattices. A proof-of-concept calculation has been carried out for p-type regimented superlattice of Ge dots on Si. It is shown that when conditions for miniband formations are satisfied, carrier transport in such structures can be tuned in a favorable way leading to large carrier mobility, Seebeck coefficient, and, as a result, to the thermoelectric figure-of-merit enhancement. To maximize the improvement, one has to tune the parameters of quantum dot superlattice in such a way that electrical current is mostly through the well-separated minibands of relatively large width (at least several kBT, where kB is Boltzmann’s constant and T is temperature). © 2003 American Institute of Physics.
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73.63.Kv Quantum dots
72.20.Pa Thermoelectric and thermomagnetic effects
73.21.La Quantum dots
72.20.Fr Low-field transport and mobility; piezoresistance

Exciton relaxation processes in colloidal core/shell ZnSe/ZnS nanocrystals

Mauro Lomascolo, Arianna Cretì, Gabriella Leo, Lorenzo Vasanelli, and Liberato Manna

Appl. Phys. Lett. 82, 418 (2003); http://dx.doi.org/10.1063/1.1537050 (3 pages) | Cited 17 times

Online Publication Date: 15 January 2003

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Colloidal ZnSe nanocrystals are coated with a ZnS shell and are investigated by means of time-resolved photoluminescence spectroscopy. These nanocrystals are stable against photooxidation and have photoluminescence quantum efficiencies around 15% even months after the synthesis. Recombination processes are investigated as a function of the excitation intensity and the emission energy. Nonlinear processes such as Auger recombination dominate in the early times after the photogeneration of electron-hole pairs. The lifetime of single exciton states is shorter in smaller ZnSe dots than in larger ones, in accordance with theoretical predictions and as previously observed on similar systems. © 2003 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena
81.05.Dz II-VI semiconductors
73.21.La Quantum dots
73.63.Kv Quantum dots
81.07.Ta Quantum dots
61.46.-w Structure of nanoscale materials
73.63.Bd Nanocrystalline materials
81.07.Bc Nanocrystalline materials
82.70.Dd Colloids
78.47.-p Spectroscopy of solid state dynamics
73.22.Lp Collective excitations
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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