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15 Feb 2000

Volume 87, Issue 4, pp. 1593-2066

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Characterization of AlxGa1−xAs/GaAs heterojunction bipolar transistor structures using cross-sectional scanning force microscopy

P. A. Rosenthal, E. T. Yu, R. L. Pierson, and P. J. Zampardi

J. Appl. Phys. 87, 1937 (2000); http://dx.doi.org/10.1063/1.372116 (6 pages) | Cited 11 times

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We have characterized base-layer width and dopant distributions on cleaved cross-sections of AlxGa1−xAs/GaAs heterojunction bipolar transistor (HBT) structures using a variation of electrostatic force microscopy. The contrast observed is sensitive to the local dopant concentration through variations in the depletion layer depth extending into the sample surface, and enables delineation of individual device regions within the epitaxial layer structure with nanoscale spatial resolution. In two epitaxially grown HBT structures, one with 50 nm base width and the other with 120 nm base width, we are able to delineate clearly the emitter, base, collector, and subcollector regions, and to distinguish regions within the collector differing in dopant concentration by a factor of two. We have also distinguished clearly between the base widths in these samples and have precisely measured the difference to be 63±3 nm, in excellent agreement with the nominal difference of 70±7 nm. © 2000 American Institute of Physics.
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85.30.Pq Bipolar transistors
85.30.De Semiconductor-device characterization, design, and modeling
61.72.S- Impurities in crystals

Experimental studies of the multimode spectral emission in quantum dot lasers

A. Patanè, A. Polimeni, L. Eaves, M. Henini, P. C. Main, P. M. Smowton, E. J. Johnston, P. J. Hulyer, E. Herrmann, G. M. Lewis, and G. Hill

J. Appl. Phys. 87, 1943 (2000); http://dx.doi.org/10.1063/1.372117 (4 pages) | Cited 7 times

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We investigate the electroluminescence spectra of edge-emitting lasers having self-assembled quantum dots as the active medium. A broad laser emission is observed with a modulation of intensity corresponding to single or bunches (supermodes) of Fabry–Pérot modes. The variation of the laser spectra with magnetic field shows that the supermodes originate from laser cavity effects and are not related directly to the electronic properties of the quantum dots. Measurements taken on devices of different cavity height, length, and lateral width indicate that the important parameter controlling the laser multimode emission is the cavity height, effectively the substrate thickness. In particular, the period of the supermodes is inversely proportional to this thickness, indicating that the modulation of the laser emission intensity is due to the leakage of modes into the transparent substrate. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors

Thermal stability of a Si/Si1−xGex quantum well studied by admittance spectroscopy

Feng Lin, Da-wei Gong, Chi Sheng, Fang Lu, and Xun Wang

J. Appl. Phys. 87, 1947 (2000); http://dx.doi.org/10.1063/1.372118 (4 pages)

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The thermal stability of a SiGe/Si quantum well grown by molecular-beam epitaxy is studied by using the admittance spectroscopy technique. The values of activation energies of hole emission from the subbands in the SiGe/Si quantum well are derived from the admittance spectra. After annealing the sample at different temperatures, the activation energy varies in different behaviors. There is no significant change of the activation energy after annealing at 700 °C for 40 min. At the annealing temperature of 900 °C, the decrease of the activation energy with annealing time could be attributed to the interdiffusion of Ge, Si atoms at the heterointerfaces and the strain relaxation effect. An unexpected phenomenon is observed at the annealing temperature of 800 °C, i.e., the activation energy increases with the annealing time. This extraordinary phenomenon is supposed to be caused by the change of the well potential shape due to the B out-diffusion from the well to the Si barrier. © 2000 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
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing

Voltage shift phenomena introduced by reverse-bias application in multilayer organic light emitting diodes

Dechun Zou and Tetsuo Tsutsui

J. Appl. Phys. 87, 1951 (2000); http://dx.doi.org/10.1063/1.372119 (6 pages) | Cited 3 times

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The effects of reverse-bias on the current–voltage (I–V) and luminance–voltage (L–V) properties of organic light-emitting diodes (OLEDs) were systematically measured. Shifts toward lower voltage both in I–V and L–V curves were observed for the OLEDs treated by reverse-bias application. The voltage-shift phenomena were discussed based on the effective drive voltage change induced by reverse bias application and the voltage-shift process was analyzed by using a relaxation model. Good consistency between experimental results and model calculations was obtained. It was found that the voltage shift process has several time constants. For example, three time constants (t01=17.9 s, t02=507 s, t03=7169 s) exist in the voltage shift process for ITO/TPD/Alq3/Mg:Ag diodes. The voltage shifts are assumed to be closely related to the movement of ionic impurities and rotations of permanent dipoles in organic layers. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.60.Bt Optoelectronic device characterization, design, and modeling
73.61.Ph Polymers; organic compounds
73.61.At Metal and metallic alloys

Recoil implantation method for ultrashallow p+/n junction formation

Henley L. Liu, Steven S. Gearhart, John H. Booske, and Reid F. Cooper

J. Appl. Phys. 87, 1957 (2000); http://dx.doi.org/10.1063/1.372120 (6 pages)

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A recoil implantation technique is investigated for ultrashallow p+/n junction formation. In this method, a 3–35 nm thick B layer is deposited on the wafer by magnetron sputtering. Then a medium energy (10–40 keV) Ge implant drives the boron atoms into Si by means of ion beam mixing. The remainder of the boron film is chemically etched away prior to the annealing step. Sub-60 nm deep p+/n junctions with sheet resistance less than 1000 Ω/sq and test diodes with leakage current density below 2 nA/cm2 have been formed using this method. © 2000 American Institute of Physics.
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61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
64.75.-g Phase equilibria
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.65.Cf Surface cleaning, etching, patterning
61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation

Energy filters using modulated superlattices

Q. K. Yang and A. Z. Li

J. Appl. Phys. 87, 1963 (2000); http://dx.doi.org/10.1063/1.372121 (5 pages) | Cited 8 times

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In this article, we demonstrate that a randomly chosen “Λ” shape modulated superlattice can serve as a better energy filter than an unmodulated superlattice. The oscillation of transmission probability in the minibands of the Λ shape modulated superlattice is shown to be greatly suppressed. We also demonstrate that precise control of the potential shape is not crucial for energy filters. The results should have prospective application in quantum cascade lasers, in which the improved energy filter can serve as the injection/relaxation region between active regions. © 2000 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Near-ultraviolet electroluminescent performance of polysilane-based light-emitting diodes with a double-layer structure

Satoshi Hoshino, Keisuke Ebata, and Kazuaki Furukawa

J. Appl. Phys. 87, 1968 (2000); http://dx.doi.org/10.1063/1.372122 (6 pages) | Cited 20 times

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We fabricated double-layer light-emitting diodes (LEDs) by utilizing poly[bis(p-nbutylphenyl)silane] (PBPS) and oxadiazole derivatives, and investigated their basic LED characteristics. The near-ultraviolet electroluminescence (EL) performance, such as the EL threshold electric field and the current density, depended on the oxadiazole derivatives used as the electron transport materials as well as the components of the EL emission. We observed better EL performance where the EL external quantum efficiency in a double-layer LED with a 2-(4′-tert-butylphenyl)-5-(4″-biphenyl)-1,3,4-oxadiazole based electron transport layer was twice that of a PBPS single-layer LED. By contrast, we observed a worse EL threshold electric field and current density when we used 2,5-bis(1-naphthyl)-1,3,4-oxadiazole as an electron transport material. The reason for the difference in the EL performance was revealed by investigating the charge carrier injection and transport dynamics of the two LEDs. © 2000 American Institute of Physics.
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42.70.Jk Polymers and organics
85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds

Device model investigation of bilayer organic light emitting diodes

B. K. Crone, P. S. Davids, I. H. Campbell, and D. L. Smith

J. Appl. Phys. 87, 1974 (2000); http://dx.doi.org/10.1063/1.372123 (9 pages) | Cited 72 times

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Organic materials that have desirable luminescence properties, such as a favorable emission spectrum and high luminescence efficiency, are not necessarily suitable for single layer organic light-emitting diodes (LEDs) because the material may have unequal carrier mobilities or contact limited injection properties. As a result, single layer LEDs made from such organic materials are inefficient. In this article, we present device model calculations of single layer and bilayer organic LED characteristics that demonstrate the improvements in device performance that can occur in bilayer devices. We first consider an organic material where the mobilities of the electrons and holes are significantly different. The role of the bilayer structure in this case is to move the recombination away from the electrode that injects the low mobility carrier. We then consider an organic material with equal electron and hole mobilities but where it is not possible to make a good contact for one carrier type, say electrons. The role of a bilayer structure in this case is to prevent the holes from traversing the device without recombining. In both cases, single layer device limitations can be overcome by employing a two organic layer structure. The results are discussed using the calculated spatial variation of the carrier densities, electric field, and recombination rate density in the structures. © 2000 American Institute of Physics.  
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85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling

1/f noise modeling in long channel amorphous silicon thin film transistors

J. Rhayem, D. Rigaud, M. Valenza, N. Szydlo, and H. Lebrun

J. Appl. Phys. 87, 1983 (2000); http://dx.doi.org/10.1063/1.372124 (7 pages) | Cited 13 times

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1/f noise investigations in thin film transistors with long channel and thin thickness of amorphous silicon film are presented. It is found that the noise behavior follows the mobility fluctuation model in ohmic and saturation regimes, whereas in the subthreshold conduction, a quadratic law versus the drain current is observed. The noise modeling is proposed taking into account the equations usually utilized for crystalline silicon metal–oxide–semiconductor field-effect transistors according to Hooge’s theory. Moreover, the Berkeley Short-Channel Insulated Gate Field-Effect Transistor Model is adapted to predict the noise levels. Two noise parameters have been extracted: The first is used in the subthreshold region, whereas we show that the second, directly related to Hooge’s parameter, is adequate to describe alone the noise in normal conduction up to the saturation. © 2000 American Institute of Physics.
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73.61.Jc Amorphous semiconductors; glasses
85.30.Tv Field effect devices
72.70.+m Noise processes and phenomena
85.30.De Semiconductor-device characterization, design, and modeling
73.61.Cw Elemental semiconductors

Effects of strained layer near SiO2–Si interface on electrical characteristics of ultrathin gate oxides

Koji Eriguchi, Yoshinao Harada, and Masaaki Niwa

J. Appl. Phys. 87, 1990 (2000); http://dx.doi.org/10.1063/1.372125 (6 pages) | Cited 10 times

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Ultrathin gate oxides formed by different process technologies are investigated in detail. The following important evidence is found: the discrepant result on the two time-dependent dielectric breakdown (TDDB) lifetime measurements, the constant-current stress, and the constant-voltage stress. The discrepancy is due mainly to the difference in the oxide leakage characteristics. Apparent changes in the activation energy and the defect generation rate during the TDDB testing are also experimentally observed for the two oxides formed by different process technologies. From the analysis based on the x-ray photoelectron spectroscopy by means of the oxide etch by dilute HF and the Fourier-transform infrared attenuated total reflection method, we consider that the above phenomena are induced by the difference in the built-in compressive strain of the Si–O network near the SiO2 and Si interface. © 2000 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.22.Jp Dielectric breakdown and space-charge effects
79.60.Jv Interfaces; heterostructures; nanostructures
78.30.Am Elemental semiconductors and insulators
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