Semiconductor Properties of Recrystallized Silicon in Aluminum Alloy Junction Diodes

Abstract

This is a study of the basic electrical properties of thin recrystallized regions formed in the fabrication of PN junctions by the alloying of pure aluminum on N-type silicon single crystals. The average aluminum concentration is about 7×1018 cm−3, and varies by a factor of 4 to 5; being largest in the region first recrystallized and decreasing in a linear manner to the surface immediately beneath the aluminum-silicon eutectic. The average Hall-hole mobility is about 55 cm2 volt−1 sec−1 and varies from 35 to 75 cm2 volt−1 sec−1 across a region formed by precipating from 977°C to the eutectic. Across the same region the conductivity varies from 72 to 35 mho cm−1. The built-in field which is both a function of depth and total width can vary from 10 to 200 v per cm in typical cases. The minority carrier (electron) diffusion length ranges from 4 to 12 μ. The temperature dependence of the distribution coefficient corresponds to an enthalpy change (differential heat of solution) of +0.43 ev necessary for the transfer of an atom of aluminum from the liquid to the solid.

Binary Phase Diagrams and Thermodynamic Properties of Silicon and Essential Doping Elements (Al, As, B, Bi, Ga, In, N, P, Sb and Tl)

“…This is due to the high entropy of the disordered state, which results in forming defects such as vacancies [ 28 ]. This behavior is called retrograde or inverse solubility [ 28 , 29 ]. The retrograde solubility phenomenon occurs during solidification and originates from a miscibility gap in the free energy of mixing [ 30 ].…”

“…In addition to the experimental errors, the data scattering could be due to the presence of low concentration impurities, which reduce the accuracy of the measurements. Gudmundsen and Maserjian [ 29 ], using thermal gradient experiments and spectrophotometric analysis, measured the solubility of Al in Si as 2.9 × 10 −4 and 2.4 × 10 −4 at % at 715 °C and 720 ± 10 °C, respectively, as compared to Mondolfo [ 65 ] who reported the solubility of Al in Si to be ranging from 1 × 10 −2 at % at 1327 °C to 1.15 × 10 −2 at % at 997 °C. Navon and Chernyshov [ 68 ] measured the solubility of Al in Si in the 700–1200 °C temperature range using resistivity measurements.…”

“… Magnified part of the Si-rich side of the Al-Si phase diagram; ―: [ 58 ]; -----: [ 59 ]; -·-·-: [ 87 ]; ····: [ 88 ]; ■: [ 29 ]; ●: [ 65 ]; □: [ 68 ]; ○: [ 69 ]; Δ (EPMA): [ 70 ], ▼ (Hall measurements): [ 70 ]; ◇: [ 89 ]. …”

Photovoltaic Measurements in Single-Nanowire Silicon Solar Cells

“…25,26 At temperatures above the Al-Si eutectic point (577 °C), a p-n aluminum alloy junction solar cell can be formed in n-type silicon, because after cooling Al acts as a p-type dopant in the recrystallized Si. 27 Regardless of the nature of the junction, excellent rectification behavior was obtained (Figure 2a).…”

“…Al contacts to planar Si have been used previously to fabricate photovoltaic devices, either as Schottky junctions , or as aluminum alloy p-n junction diodes . Schottky photovoltaic devices are possible because annealed Al−Si contacts can exhibit Schottky barrier heights of up to 0.8 V with increasing heat treatment temperatures. , At temperatures above the Al−Si eutectic point (577 °C), a p-n aluminum alloy junction solar cell can be formed in n-type silicon, because after cooling Al acts as a p-type dopant in the recrystallized Si a).…”