Characteristic Comparison Between Ge-on-Insulator (GOI) and SI-on-Insulator (SOI) Beam-Induced Crystallization Mechanism
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CHARACTERISTIC COMPARISON BETWEEN Ge-ON-INSULATOR (GOI) AND SI-ON-INSULATOR (SOI) BEAM-INDUCED CRYSTALLIZATION MECHANISM El-Hang Lee and M. Abdul Awal AT&T Laboratories Engineering Research Center P.O. Box 900, Princeton, NJ 08540 U.S.A.
ABSTRACT Characteristics of beam-recrystallized Si-on-insulator (SOT) and Ge-on-insulator (GOI) material systems are compared for the first time to gain complementary understanding of the crystallization mechanism that would benefit both systems. In general, GOI has been found to behave quite differently from SOL. In SOI, Si yields sub-boundaries; in GOI, Ge generates twinned or faceted crystals. In GOI, too, sub-boundary-like features were observed, but only occasionally in the midst of twinned crystals. Also observed in GOI was the phenomenon of seeded crystallization breakdown, where defect-free crystals from the seed abruptly turn into defect-laced crystals at a certain distance from the seed. This phenomenon is highly characteristic in SO, but has never been reported for GOI. These findings are compared and discussed in light of the traditional understanding of crystal growth. INTRODUCTION Both Si-on-insulator (SOI) [1] and Ge-on-insulator (GOI) [2] are considered technologically important materials, the former for high-speed, high-density, and radiationhardened circuit applications and the latter for integrated opto-electronic circuit applications. In the latter, GaAs layers are lattice-matched to Ge layers to achieve dielectrically-isolated GaAs-on-Si [3].
The dielectric isolation, in particular, offers the
potential to enable three-dimensional (3-D) circuit applications for both electronic devices and photonic devices. The concept of 3-D applications has been vigorously pursued in the SOI technology [4]. One of the popular approaches to achieving SOI has been the energy-beam-induced zone-melt recrystallization technique. A fundamentally significant issue in this technique is the pervasive occurence of low-angle grain-boundaries, or sub-boundaries. While many schemes have been devised to suppress or entrain sub-boundaries, a more complete and fundamental understanding is still required, especially from a new perspective. Germanium belongs to the group IV family, like Si. Both elements solidify in a diamond structure, having similar lattice constants (5.658 A and 5.431 A, respectively), but differ in melting temperature, thermal conductivity, thermal expansion, and wetting characteristics on insulators. A comparative study of GOI and SOI will thus provide a complementary understanding not only for SOI but also for GOI, benefiting both material systems. Similarities and dissimilarities of morphological variation, both in seeded and unseeded crystallization between the SOI and GOI, are examined, for the first time, in light of the traditional understanding of the crystal growth mechanism. Here we focus mainly on the crystallization mechanism. General descriptions of the recrystallization phenomena including crystallinity, defect, seeding, capping, ambient pressure and other
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