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4 Feb 2002

Volume 80, Issue 5, pp. 707-899

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Two-color quantum-well infrared photodetector with voltage tunable peaks

Amlan Majumdar, K. K. Choi, J. L. Reno, L. P. Rokhinson, and D. C. Tsui

Appl. Phys. Lett. 80, 707 (2002); http://dx.doi.org/10.1063/1.1447004 (3 pages) | Cited 15 times

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A two-color quantum-well infrared photodetector with voltage tunable detection peaks is demonstrated. It is based on electron transfer between two asymmetric coupled quantum wells under an applied bias. At 10 K, the peak detection wavelength is 7.5 μm for positive bias when the electrons reside in one of the wells, and switches to 8.8 μm at a large negative bias when the electrons are transferred to the other well. The electron activation behavior of dark current in this detector depends on both temperature and bias. We observed two distinctive activation energies under negative bias for two different temperature regimes and only one under positive bias. The voltage tunability of the detector and the activation energy are well explained by the calculated energy levels and oscillator strengths of intersubband transitions in the structure. © 2002 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
81.05.Ea III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.Fg Quantum wells
78.67.De Quantum wells
81.07.St Quantum wells

Ag photodoping into crystalline ZnSe

Hyun-Yong Lee, Joon-Suk Song, Hisao Makino, and Takafumi Yao

Appl. Phys. Lett. 80, 710 (2002); http://dx.doi.org/10.1063/1.1445464 (3 pages) | Cited 5 times

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We have investigated the possibility of Ag photodoping into crystalline (c-) ZnSe grown by molecular-beam epitaxy. A Ag/c-ZnSe sample was illuminated with a 325 nm HeCd laser at 10 K and its photoluminescence (PL) characteristics were measured in real time. Depending on the illumination time, there are considerable changes in the intensities of the deep-level peaks (2.059 and 2.345 eV) as well as the near-band-edge peak (2.798 eV). The emission band at 2.059 eV is almost independent of PL-excitation power, while the green luminescence band at 2.345 eV exhibits distinctly a power-dependent blueshift with increasing excitation power, which can be assigned as a donor-to-acceptor pair transition (AgiAgZn). In this letter, a model to explain Ag photodoping into c-ZnSe is proposed on the basis of the PL results. We believe that Ag, as an activator for luminescence, can be photodoped into c-ZnSe even though the extent and kinetics of the Ag doping are different from those of the amorphous chalcogenide. © 2002 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors
78.66.Hf II-VI semiconductors

Red electrophosphorescence from osmium complexes

Xuezhong Jiang, Alex K.-Y. Jen, Brenden Carlson, and Larry R. Dalton

Appl. Phys. Lett. 80, 713 (2002); http://dx.doi.org/10.1063/1.1445272 (3 pages) | Cited 27 times

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We report red electrophosphorescence from light-emitting diodes based on osmium (Os) complexes. Efficient red emission was achieved using an in situ polymerized tetraphenyldiaminobiphenyl-containing polymer as the hole-transporting layer and Os complexes doped blend of poly(N-vinylcarbazole) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole as the emitting layer. The emission peaks of the reported Os complexes, ranging from 620 to 650 nm, can be tuned by changing the structures of the ligands because the emission originates from triplet metal-to-ligand-charge-transfer excited state. The Os complexes trap both electrons and holes, which facilitates the direct recombination of holes and electrons on the complex sites. The peak external quantum efficiency and brightness achieved from the complexes were 0.82% and 970 cd/m2, respectively. The Commission Internationale de I’Eclairage chromaticity coordinates (x,y) for the best red emission from the complexes are (0.65, 0.33). © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices

Optically written solid-state lasers with broadly tunable mode emission based on improved poly (2,5-dialkoxy-phenylene-vinylene)

G. Kranzelbinder, E. Toussaere, J. Zyss, A. Pogantsch, E. W. J. List, H. Tillmann, and H.-H. Hörhold

Appl. Phys. Lett. 80, 716 (2002); http://dx.doi.org/10.1063/1.1445473 (3 pages) | Cited 21 times

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We report an optical written distributed feedback (DFB) structure with broadly and continuously tunable mode emission (Δλ = 30 nm) based on polycondensation-type poly[2methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH–PPV). In a Lloyd-mirror configuration we realize first-order feedback by dynamic photoinduced in-plane gratings, which can also be imprinted permanently. This technique is a versatile fabrication tool for polymeric DFB laser structures while also providing an efficient method to probe the lasing performance of organic solid-state laser materials. Furthermore, features of the photoinduced absorption spectra of improved MEH–PPV indicate favorable material properties towards further homopolymer solid-state laser applications. © 2002 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials
42.70.Jk Polymers and organics
42.79.Bh Lenses, prisms and mirrors
42.79.Dj Gratings

Fourier-transform photocurrent spectroscopy of microcrystalline silicon for solar cells

M. Vanecek and A. Poruba

Appl. Phys. Lett. 80, 719 (2002); http://dx.doi.org/10.1063/1.1446207 (3 pages) | Cited 43 times

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The spectral dependence of the optical absorption coefficient in thin films of hydrogenated microcrystalline silicon is measured over nine orders of magnitude in the subgap, defect-connected region, and in the above-the-band gap region. Transmittance, reflectance, and constant photocurrent method measurements are combined with Fourier-transform photocurrent spectroscopy (FTPS). Results are analyzed and interpreted as due to electron transitions from defects or interband electron transitions, all having direct relevance to the thin-film microcrystalline silicon solar cell performance. FTPS is a fast and sensitive quantitative method for quality assessment of microcrystalline silicon absorber in solar cells and can be used for quality monitoring in solar cell production. © 2002 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
72.40.+w Photoconduction and photovoltaic effects
78.66.Jg Amorphous semiconductors; glasses
78.66.Db Elemental semiconductors and insulators
72.80.Cw Elemental semiconductors
73.61.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
81.05.Gc Amorphous semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
84.60.Jt Photoelectric conversion

Observation of enhanced spontaneous emission coupling factor in nitride-based vertical-cavity surface-emitting laser

S. Kako, T. Someya, and Y. Arakawa

Appl. Phys. Lett. 80, 722 (2002); http://dx.doi.org/10.1063/1.1430855 (3 pages) | Cited 15 times

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We demonstrate an enhancement of spontaneous emission coupling factor β in a nitride-based vertical-microcavity surface-emitting laser. The 2.5λ vertical microcavity, the quality factor of which reaches 740, is sandwiched between a nitride and an oxide distributed Bragg reflector. From input–output measurements and analyses of the rate equations, the β of the lasing mode at a wavelength of 396.1 nm is estimated to be 1.6×10−2. The estimated β can be well accounted for by a simple theoretical model. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.50.-p Quantum optics

Graded mixed-layer organic light-emitting devices

Anna B. Chwang, Raymond C. Kwong, and Julie J. Brown

Appl. Phys. Lett. 80, 725 (2002); http://dx.doi.org/10.1063/1.1446992 (3 pages) | Cited 69 times

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We describe the performance of graded, mixed-layer organic light- emitting devices (OLEDs). The devices are step graded from a mostly hole transporting layer (HTL) to a mostly electron transporting layer (ETL) from anode side to cathode side, respectively. Luminous efficiencies of >4.5 lm/W and 10 cd/A are obtained at 1000 cd/m2 for green, electrofluorescent, graded mixed OLEDs. These efficiencies are significantly higher than those of a uniformly mixed device, i.e., a device in which the HTL and ETL are uniformly mixed, but lower than those of a conventional heterostructure device employing the same dopant material. The operating lifetime of the graded mixed OLEDs, however, is much improved over the heterostructure device. The results of our work suggest that the graded mixed OLED device structure represents a path to achieving extended lifetimes with sufficient efficiency for flat panel display applications in which this parameter is critical to market acceptance. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.60.Pg Display systems

Ga flux dependence of Er-doped GaN luminescent thin films

D. S. Lee and A. J. Steckl

Appl. Phys. Lett. 80, 728 (2002); http://dx.doi.org/10.1063/1.1447318 (3 pages) | Cited 15 times

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Er-doped GaN thin films have been grown on (111) Si substrates with various Ga fluxes in a radio frequency plasma molecular beam epitaxy system. Visible photoluminescence (PL) and electroluminescence (EL) emission at 537/558 nm and infrared (IR) PL emission at 1.5 μm from GaN:Er films exhibited strong dependence on the Ga flux. Both visible and IR PL and visible EL increase with the Ga flux up to the stoichiometric growth condition, as determined by growth rate saturation. Beyond this condition, all luminescence levels abruptly dropped to the detection limit with increasing Ga flux. The Er concentration, measured by secondary ion mass spectroscopy and Rutherford backscattering, decreases with increasing Ga flux under N-rich growth conditions and remains constant above the stoichiometric growth condition. X-ray diffraction indicated that the crystalline quality of the GaN:Er film was improved with increasing Ga flux up to stoichiometric growth condition and then saturated. Er ions in the films grown under N-rich conditions appear much more optically active than those in the films grown under Ga-rich conditions. © 2002 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
78.60.Fi Electroluminescence
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Holographic recording of fast phenomena

Zhiwen Liu, Gregory J. Steckman, and Demetri Psaltis

Appl. Phys. Lett. 80, 731 (2002); http://dx.doi.org/10.1063/1.1446205 (3 pages) | Cited 13 times

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We report on a holographic method for recording fast events whose speed is limited by the laser pulse duration if the recording material has sufficient sensitivity to reliably record a frame of the fast event with a single pulse. The method we describe uses the angular selectivity of thick holograms to resolve frames that are recorded with adjacent pulses. Two specially designed cavities are used to generate the signal and reference pulse trains. We experimentally demonstrate the system by recording laser induced shock waves with a temporal resolution of 5.9 ns, limited by the pulse width of the Q-switched Nd:yttrium–aluminum–garnet laser used in the experiments. © 2002 American Institute of Physics.
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42.40.Ht Hologram recording and readout methods
06.60.Jn High-speed techniques (microsecond to femtosecond)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Evidence for bandedge lasing in a two-dimensional photonic bandgap polymer laser

N. Moll, R. F. Mahrt, C. Bauer, H. Giessen, B. Schnabel, E. B. Kley, and U. Scherf

Appl. Phys. Lett. 80, 734 (2002); http://dx.doi.org/10.1063/1.1446213 (3 pages) | Cited 22 times

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See Also: Erratum

Show Abstract
Optically pumped organic semiconductor lasers are fabricated by spincoating a thin film of a methyl-substituted ladder-type poly-(para-phenylene) onto a nanopatterned circular grating distributed Bragg reflector. Varying the period of the grating allows for tunability of the laser wavelength. Comparing the emission spectra below and above the threshold shows that the lasing is spectrally located at the bandedge of the Bragg dip. This is in excellent agreement with the calculated dispersion relation of the laser system. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.70.Jk Polymers and organics
42.70.Qs Photonic bandgap materials
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
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