Issues in the Growth of Bulk Crystals of Infrared Materials
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ISSUES IN THE GROWTH OF BULK CRYSTALS OF INFRARED MATERIALS K. J. BACHMANN AND H. GOSLOWSKY
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204. ABSTRACT Selected issues in the growth of bulk single crystals for applications in infrared optoelectronics are reviewed including an overview over materials choices, bulk III-V crystal growth, and the growth of II-VI, IV-VI and I-III-VI 2 compounds and alloys.
The most important issues are the
control of purity, perfection, stoichiometry, and uniformity during crystal growth and the control of the surface properties in wafer fabrication. Specific examples are given to illustrate problems related to these issues and to discuss approaches to their solution. 1.
INTRODUCTION
The infrared (IR) wavelength region extends from X = 780 nm to infinity and is customarily divided into the near (0.78 < X < 3 vam), intermediate (3 < X < 30 vim) and far (X > 30 Pm) regimes. Cons-equei-tly semiconductors that are iuitable for the fabrication of IR devices have band gaps 0 < Eg < 1.6
eV.
Several classes of compounds have members in this energy region, e.g.
the tetrahedrally coordinated group IV semiconductors and their III-V, IIVI, II-IV-V2 and I-III-VI 2 isoelectronic analogs as well as the NaCl structure IV-VI compounds. 2.0
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70 Figure 1 shows a plot Eg vs. a-axis lattice parameter for these compounds. The data refer to the smallest gaps at room temperature between which continuous band gap and lattice constant tailoring is possible within the existence ranges of solid solutions. For applications in the near IR the III-V compounds and alloys are usually preferred because of their direct band gaps and well behaved extrinsic doping properties. The intermediate and far IR are covered by the II-VI and IV-VI alloys, in particular the CdxHgl.xTe and SnxPblxTe systems that exhibit at room temperature zero gap
at x = 0.1 and x = 0.59, respectively. Landau level absorption and emission in the range 70 pm < X < 500 m has been reported for bulk InSb /1/ that, also, is an importaiit detector material for wavelengths in the intermediate
IR extending in the form of alloys to the 8-10 pm region /2/. We note that although solid solubility over the entire range of compo-
sitions 0 < x < I has been assumed for most of the pseudobinary III-V alloys in The -early literature, in the past decade, extended regions of immiscibility in solid state have been identified on the basis of classical thermodynamic calculations for many III-V systems /3/. Also, ordering at distinct compositions below a critical t
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