G. B. Anderson

Control of silicon network structure in plasma deposition

Abstract Controllability of the Si network structure ranging from amorphous to microcrystalline, polycrystalline, or epitaxial growth has been achieved in conventional glow discharge of silane by controlling the extent of hydrogen ‘etching’ during film growth. The concept of film formation as a balance between deposition and ‘etching’ of the growing surface is discussed. Since energetically unfavorable configurations are preferentially eliminated, ‘etching’ reduces the temperature required to remove weak or strained bonds and produces device quality a-Si:H. It is also responsible for achieving low temperature crystallinity.

LASER DEHYDROGENATION/CRYSTALLIZATION OF PLASMA-ENHANCED CHEMICAL VAPOR DEPOSITED AMORPHOUS SILICON FOR HYBRID THIN FILM TRANSISTORS

A low temperature process for laser dehydrogenation and crystallization of hydrogenated amorphous silicon (a‐Si:H) has been developed. This process removes hydrogen by laser irradiations at three energy steps. Studies of hydrogen out‐diffusion and microstructure show that hydrogen out‐diffusion depends strongly on film structure and the laser energy density. Both high quality and low leakage bottom gate polycrystalline silicon and a‐Si:H thin film transistors were monolithically fabricated on the same Corning 7059 glass substrate with a maximum process temperature of only 350 °C.

Epitaxial MgO on GaAs(111) as a buffer layer for z‐cut epitaxial lithium niobate

The epitaxial system z‐lithium niobate on GaAs(111)A and GaAs(111)B has been demonstrated by in situ pulsed laser deposition both with and without intermediate layers of MgO(111). The in‐plane epitaxial relationships are LiNbO3[110]∥GaAs[211] and [211] indicating the existence of 180° boundaries in the LiNbO3 both with and without the MgO layer, which grows cube‐on‐cube with the GaAs. Out‐of‐plane texture is typically 1.0° and 1.2° for the MgO and LiNbO3 layers, respectively. In‐plane texture is typically 2.8° and 4.5° for the MgO and LiNbO3 layers, respectively. This epitaxial system may be useful for monolithic electro‐optic or frequency doubling applications in conjunction with semiconductor laser diodes.

Low temperature crystallization of amorphous silicon using an excimer laser

Low temperature processing is a prerequisite for compatible technologies involving combined a-Si and poly-silicon devices or for fabricating these devices on glass substrates. This paper describes excimer-laser-induced crystallization of thin amorphous silicon films deposited by plasma CVD (a-Si:H) and LPCVD (a-Si). The intense, pulsed UV produced by the laser is highly absorbed by the thin amorphous material, but the average temperature is compatible with low temperature processing. The process produces crystallites whose structure and electrical characteristics vary according to starting material and laser scan parameters. The crystallized films have been principally characterized using x-ray diffraction, TEM, and transport measurements. The results indicate that crystallites nucleate in the surface region and are randomly oriented. The degree of crystallization near the surface increases as the doping level and/or deposited laser energy density is increased. The crystallite size increases with a power law dependence on deposited energy, while the conductivity increases exponentially above threshold for unintentionally doped PECVD films. The magnitude of the Hall mobility of the highly crystallized samples is increased by two orders of magnitude over that of the amorphous starting material.

Hydrogen in crystalline semiconductors

Abstract The range of phenomena associated with the introduction of hydrogen into single-crystal semiconductors is reviewed with emphasis on the following current topics: dissociation of hydrogen-dopant complexes, diatomic hydrogen complexes, and hydrogen-induced defects. Included is a tabulation of the parameters that have thus far been deduced from experimental studies on hydrogen-dopant complexes and hydrogen migration in crystalline silicon and gallium arsenide.

Preparation of oriented Bi-Ca-Sr-Cu-O thin films using pulsed laser deposition

Oriented c‐axis thin films of Bi‐Ca‐Sr‐Cu‐O on [100] SrTiO3 substrates have been fabricated using the pulsed excimer laser evaporation technique. Deposition at room temperature in 1 mTorr oxygen followed by an 875 °C anneal in oxygen yields superconducting films with zero resistance at 80 K and a resistivity drop near 110 K, hinting at the presence of another superconducting phase. Transmission electron microscopy shows that the films are epitaxial with the substrate, with an abrupt and planar interface boundary. The observed crystal structure is consistent with diffraction results on bulk materials.

Excimer‐laser‐induced crystallization of hydrogenated amorphous silicon

The electronic transport properties and structural morphology of fast‐pulse excimer‐laser‐ crystallized hydrogenated amorphous silicon (a‐Si:H) thin films have been measured. The room‐temperature dark dc conductivities and Hall mobilities increase by several orders of magnitude at well‐defined laser energy density thresholds which decrease as the impurity concentration in the films increases. The structural morphology of the films suggests an impurity‐induced reduction of the a‐Si:H melt temperature as the origin of this behavior.

Enthalpy array analysis of enzymatic and binding reactions

Enthalpy arrays enable label-free, solution-based calorimetric detection of molecular interactions in a 96-detector array format. The combination of the small size of the detectors and the ability to perform measurements in parallel results in a significant reduction of sample volume and measurement time compared with conventional calorimetry. We have made significant improvements in the technology by reducing the temperature noise of the detectors and improving the fabrication materials and methods. In combination with an automated measurement system, the advances in device performance and data analysis have allowed us to develop basic enzyme assays for substrate specificity and inhibitor activity. We have also performed a full titration of 18-crown-6 with barium chloride. These results point to future applications for enthalpy array technology, including fragment-based screening, secondary assays, and thermodynamic characterization of leads in drug discovery.

Solid phase epitaxial growth of sol‐gel derived Pb(Zr,Ti)O3 thin films on SrTiO3 and MgO

Pb(Zr0.52Ti0.48)O3 (PZT) thin films were crystallized on SrTiO3 (100) and MgO (100) substrates by a sol‐gel process using nonhydrolyzed metal methoxyethoxide precursors, spin coating, and rapid thermal annealing. Solid phase epitaxial growth of PZT on SrTiO3 was observed directly from the amorphous phase even at 425 °C. The PZT had a single (001) orientation and rocking curve full width at half maximum (FWHM) less than 0.1°. High‐temperature annealing of MgO substrates improved orientation of PZT thin films. Epitaxial crystallization of PZT with a single (001) orientation on the annealed MgO was observed at temperature above 550 °C after the formation of the pyrochlore phase.

GRAIN GROWTH IN LASER DEHYDROGENATED AND CRYSTALLIZED POLYCRYSTALLINE SILICON FOR THIN FILM TRANSISTORS

Selective dehydrogenation and crystallization are realized by a three‐step incremental increase in laser energy density. X‐ray diffraction and transmission electron microscopy show that the polycrystalline grains formed with this three‐step process are similar to those after a conventional one‐step laser crystallization of unhydrogenated amorphous silicon. The grain size increases with increasing laser energy density up to a peak value of a few micrometers. The grain size decreases with further increases in laser energy density. The transistor field effect mobility is correlated to the material properties, increasing gradually with laser energy density until reaching its maximum value. Thereafter, the transistors suffer from leakage through the gate insulators. A dual dielectric gate insulator has been developed for these bottom‐gate thin film transistors. Our structure simplifies fabrication of both high quality amorphous and polycrystalline thin film transistors on the same glass substrate. We discuss t...