Casting of Laminated Ribbon Using a Modified Melt-Spinning Technique
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CASTING OF LAMINATED RIBBON USING A MODIFIED MELT-SPINNING TECHNIQUE
R. V. RAMAN, Battelle Columbus Laboratories, 505 King Avenue, Columbus, 43201 and A. F. WITT, Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
Ohio
ABSTRACT Laminated metal-metal and metal-semiconductor ribbons have been prepared by a modified melt-spinning technique. Characterization studies have been carried out on laminated Sn-Zn, Ge-Al, InSb-CuZr and some other materials. Characteristics of these ribbons and their potential applications will be described.
INTRODUCTION Semiconductor ribbons cast directly from the melt hold promise as low-cost materials for photovoltaic applications. In this context, a number of ribbon casting techniques are being evaluated [1-7]. The technique commonly used for the casting of metallic ribbons directly from the melt is the melt-spinning process. [8] This work was initiated with the objective of investigating the adaptability of the melt-spinning process to cast semiconductor ribbons. Semiconductor systems of main interest were silicon and gallium arsenide. However in view of the anticipated difficulties with the handling of molten silicon and gallium arsenide, it was decided that the initial feasibility study should be carried out using lower melting semiconductors - such as indium antimonide, germanium, etc. MELT SPINNING OF SEMICONDUCTOR RIBBONS Schematic of the melt-spinning apparatus used in this work is shown in Figure 1. Details of the apparatus are discussed elsewhere [9]. Melt-spun ribbons (width=l mm; thickness=30m; length=cms) of In5 0 Sb50, Ga5 0 Sb50, In2 5 Ga2^Sb5 and
Ge were prepared.
A characteristic feature of all the semiconductor riibons
prepared was their inherent brittleness, measurements and in device fabrication.
which created difficult-7 in property
Drum (cooled) ý5
Melt
L!
Crucible Heating coils
feed Q Argon
m
R.F. heater feed
Bellows
Pneumatic cylinder
Vacuum Figure 1.
Schematic of inside-of-drum melt spinning apparatus.
142 Characterization of ribbon samples in each system was carried out by optical and scanning microscopy and x-ray diffraction. In addition, for the In50Sb5O ribbon Van der Pauw Hall measurements were also carried out, to measure carrier concentration and mobility. Some structural and electrical characteristics of the melt-spun indium antimonide ribbon are compared with the electronic grade starting ingot material in Table I. The melt-spun indium antimonide ribbon has 2 orders of magnitude lower mobility than the ingot material, which is most likely due to the smaller grain size and larger number of defects in the ribbon. TABLE I. Characteristics of ribbon and ingot indium antimonide
Ingot Average Grain Size Mobility Carrier Concentration
1 mm, 7.1 x 104 cm 2/v.sec 16 -3 1.8 x 10 cm
Ribbon 10pm 3.0 x 102 cm2/v.sec 16 -3 1.2 x 10 cm
The brittleness and the small grain size of the melt-spun semiconductor ribbon appeared to be its two major drawbacks, from the viewpoint of po
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