N-type Junction Research Articles

Epitaxial InAs-coupled superconducting junctions

Homoepitaxial n-type InAs-coupled superconducting junctions are investigated. The n-type channel layer on a p-type substrate has nearly the same mobility as bulk crystal and the layer can be isolated electrically from the substrate by the built-in potential at the p-n interface. As a result, the critical current-normal resistance (IC RN ) product of the homoepitaxial n-type InAs-coupled junction is at least 30 times better than those of the bulk n-type ones. The coherence length ξN is calculated using the experimentally obtained carrier concentration, mobility, and effective mass. Temperature dependence of IC agrees with calculations based on the proximity effect theory which can be applied to the intermediate regime between the clean and dirty limits.

Electronic transport properties of epitaxial erbium silicide/silicon heterostructures

We studied electrical parallel and perpendicular transport in thin epitaxial erbium silicide films obtained by solid phase reaction and by codeposition of Er and Si on (111) Si. Resistivity measurements show that the silicide is metallic with a room-temperature resistivity of 34 μΩ cm; the dependence of the Hall coefficient on temperature can be explained by a two-band conduction model. Magnetic effects are shown to affect the low-temperature resistivity and the Hall coefficient. Perpendicular transport properties are studied by electrical [current-voltage I(V) and capacitance-voltage C(V) characteristics] and internal photoemission methods on erbium silicide/n- or p-type Si diodes. The p-type diodes have a perfect rectifying behavior with a Schottky barrier height of about 0.74 eV measured by I(V) and photoemission methods. The n-type junction is ohmic at room temperature and rectifying at low temperatures; C(V) and optical measurements yield a Schottky barrier height of about 0.28 eV. Some potential applications of erbium silicide/Si heterostructures are presented.

Photovoltaic effect of n-type polyacetylene junctions

n-Type polyacetylene (n-PA) was layered with an electrochemically synthesized polymer (polypyrrole or polythiophene) to make heterojunctions and their photovoltaic effects were investigated. The junctions showed good rectifying characteristics and photovoltaic ability. The both effects were maintained for more than one month. However, in a PA homojunction (p-PA/n-PA), the dopants compensated each other in a few days. Thus, the heterojunction is superior to the homojunction in stability. These results suggest that the dopants in the n-PA do not migrate into the polypyrrole or polythiophene layer. Both polypyrrole/n-PA and polythiophene/n-PA junctions were observed to have photoconversion efficiency of 10 −4 % under irradiation of monochromatic light.