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24 Apr 2000

Volume 76, Issue 17, pp. 2325-2474

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Threshold voltage of excimer-laser-annealed polycrystalline silicon thin-film transistors

C. T. Angelis, C. A. Dimitriadis, F. V. Farmakis, J. Brini, G. Kamarinos, and M. Miyasaka

Appl. Phys. Lett. 76, 2442 (2000); http://dx.doi.org/10.1063/1.126370 (3 pages) | Cited 8 times

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Based on experimental studies of n-channel excimer-laser-annealed polycrystalline silicon thin-film transistors with gate ratio width/length varying from 0.5 to 2.5, we propose a reliable method to determine the threshold voltage Vt from linear extrapolation of the transconductance to zero. The results reveal that the determined values of Vt are independent of the device geometry and the applied drain voltage in the linear region, in contrast with the drain current linear extrapolation method. The values of Vt are correlated with the density of the total trap states derived from the subthreshold gate swing voltage. © 2000 American Institute of Physics.
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85.30.Tv Field effect devices
81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

High-Tc gradiometric superconducting quantum interference device and its incorporation into a single-layer gradiometer

A. J. Millar, E. J. Romans, C. Carr, A. Eulenburg, G. B. Donaldson, P. Maas, and C. M. Pegrum

Appl. Phys. Lett. 76, 2445 (2000); http://dx.doi.org/10.1063/1.126371 (3 pages) | Cited 7 times

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We describe a first-order gradiometric dc superconducting quantum interference device (SQUID) and its incorporation into a first-order directly coupled single-layer gradiometer. The gradiometric SQUIDs were fabricated from a single layer of YBa2Cu3O7, with a silicon dioxide insulating layer and a gold crossover structure. For several gradiometric SQUIDs, with estimated inductances of order 67 pH, we measured parasitic effective areas in the range 1–2 μm2, approximately two orders of magnitude lower than for conventional narrow linewidth SQUIDs of similar inductance. For a single-layer gradiometer incorporating a gradiometric SQUID, we measured a parasitic effective area of 95 μm2. We demonstrate that for this device, the SQUID itself makes a negligible contribution to the overall parasitic effective area. We show that the improved balance leads to better performance in an unshielded environment. © 2000 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Hydrogenation of ZnS passivation on narrow-band gap HgCdTe

J. K. White, C. A. Musca, H. C. Lee, and L. Faraone

Appl. Phys. Lett. 76, 2448 (2000); http://dx.doi.org/10.1063/1.126372 (3 pages) | Cited 12 times

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Due to the narrow band gap of HgCdTe required for infrared photodetectors, the device performance is readily influenced by surface effects. This letter examines the effect that hydrogenation has on the quality of industry-standard ZnS passivating films. The hydrogenation is achieved by exposing the samples to a H2/CH4 plasma that is present during a reactive ion etching process. The results show a marked improvement of the passivant/substrate interface for hydrogenated devices with a reduction of the average fixed interface charge density to 3.5×1010 cm−2, accompanied by a sixfold decrease in the standard deviation. The advantage of this method of hydrogenation is that it is integrated into the reactive ion etch processing for mesa formation or p-type to n-type conversion in photoconductive or photovoltaic device fabrication, respectively. With the improvement of the ZnS passivation with hydrogenation, this method may alleviate the need for complex epitaxial passivation processing. © 2000 American Institute of Physics.
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81.65.Rv Passivation
81.05.Dz II-VI semiconductors
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
85.60.Gz Photodetectors (including infrared and CCD detectors)
81.65.Cf Surface cleaning, etching, patterning
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Peltier microcalorimeter

I. K. Moon, D. H. Jung, K.-B. Lee, and Y. H. Jeong

Appl. Phys. Lett. 76, 2451 (2000); http://dx.doi.org/10.1063/1.126373 (3 pages) | Cited 6 times

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We developed an ac microcalorimeter utilizing the Peltier effect of a thermocouple junction as an ac power source. This Peltier microcalorimeter allows us to measure the absolute value of the heat capacity of small samples with submilligrams of mass. The performance of the microcalorimeter was checked in the temperature range of 15–420 K with α-Al2O3 samples of 0.54 and 2.25 mg. The absolute accuracy was ±3% for the range of 30–150 K and ±1% for 150–420 K. The precision was better than 0.5% in the whole temperature range. © 2000 American Institute of Physics.
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07.20.Fw Calorimeters
65.40.-b Thermal properties of crystalline solids
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Improving the performance of conjugated polymer-based devices by control of interchain interactions and polymer film morphology

Thuc-Quyen Nguyen, Raymond C. Kwong, Mark E. Thompson, and Benjamin J. Schwartz

Appl. Phys. Lett. 76, 2454 (2000); http://dx.doi.org/10.1063/1.126374 (3 pages) | Cited 89 times

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Interchain interactions in conjugated polymer films promote good carrier transport but also reduce the luminescence quantum yield, leading to a fundamental trade-off in optimizing film morphology for device performance. We present two methods to improve the efficiency of light-emitting diodes (LEDs) based on poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) by altering film morphology without changing device architecture. First, “trilayer” LEDs, which use a central MEH-PPV layer with reduced interchain interactions between layers of highly aggregated MEH-PPV near the electrodes, have a higher efficiency than single-layer devices. Second, device efficiency can be improved by annealing MEH-PPV films, so that the reduced emission upon increasing interchain interactions is overcome by more balanced charge injection. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
61.41.+e Polymers, elastomers, and plastics
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials

High voltage operation (>80 V) of GaN bipolar junction transistors with low leakage

J. B. Limb, H. Xing, B. Moran, L. McCarthy, S. P. DenBaars, and U. K. Mishra

Appl. Phys. Lett. 76, 2457 (2000); http://dx.doi.org/10.1063/1.126375 (3 pages) | Cited 16 times

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We have demonstrated the high voltage operation of n-p-n GaN bipolar junction transistors using regrown emitters. Devices were grown by metalorganic chemical vapor deposition on sapphire substrates. The n-type emitter was grown selectively on a base-collector p-n junction diode using a dielectric mask. A thin base (1000 Å) was used to increase the current gain over our previous result with a regrown emitter [J. B. Limb, L. McCarthy, P. Kozodoy, H. Xing, J. Ibbetson, Y. Smorchkova, S. P. DenBaars, and U. K. Mishra, Electron. Lett. 35, 19 (1999)]. The base contacts were better than expected despite the use of a thin base. Common emitter operation showing a voltage operation of over 80 V with negligible leakage has been demonstrated. Room temperature current gain was ∼3 corresponding to a current transfer ratio of ∼0.75. This results in a calculated minority carrier lifetime of about 80 pS in the base. © 2000 American Institute of Physics.
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85.30.Pq Bipolar transistors
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
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