• PDF / 263,259 Bytes
• 6 Pages / 612 x 792 pts (letter) Page_size
• 88 Downloads / 252 Views

DOWNLOAD

REPORT

---

C3.10.1

MOCVD ZINC OXIDE FILMS FOR WIDE BANDGAP APPLICATIONS C.E. Rice, G.S. Tompa, L.G. Provost, N. Sbrockey, J. Cuchiaro; Structured Materials Industries, Inc., 201 Circle Drive North, Unit 102/103, Piscataway, NJ 08854-3908 www.structruredmaterials.com ABSTRACT ZnO is a wide bandgap (3.2 eV) semiconductor with potential application in LEDs, lasers, and transparent transistors, among other uses. These applications require uniform thickness, high quality materials (amorphous, poly- or single crystal), pinhole- and defect-free-single-and multilayer-conformal coatings. These attributes are generally best achievable by MOCVD. We have mounted a significant effort to develop automated MOCVD systems and process technologies for single and multicomponent oxides. The reactors use high speed rotation and are of a vertical orientation built to all metal UHV standards. We have demonstrated reactor scaled performance from 3” to 12” diameter depositions planes with modeling scales through 24” diameter. Metalorganics are used for zinc and dopant sources as well as dopant gases to optimize performance at low pressures. In this paper we will discuss our most recent results with epitaxial ZnO films, achievements in p-type doping, multilayer structures, and polycrystalline doped ZnO films. Introduction It is surprising that ZnO, which has a wide bandgap, has received such little attention compared to that given to semiconductors such as GaN or ZnSe. In fact, ZnO has advantages: (1) the exciton binding energy is much higher (60 meV vs 21 meV for GaN); making 300-K exciton lasing much more likely; (2) relatively large-area bulk ZnO can be grown, providing exact lattice and thermal matching to epitaxial layers (not to mention that bulk ZnO can be doped (at least ntype) or that single crystal Al2O3 could also serve as a substrate)[1]; and (3) wet chemical processing is routine with ZnO, but virtually impossible with GaN. One of the last major hurdles in implementing ZnO is routinely achieving and manipulating p-type ZnO. Several deposition techniques have been applied to grow ZnO films: evaporation[2,3], r.f.[4,5,6,7], d.c.[8,9,10,11] magnetron sputtering, ion beam sputtering [12], spray pyrolysis[13,14,15], sol-gel process[16], pulse-laser deposition[17], chemical beam deposition[18], and metal-organic chemical vapor deposition (MOCVD)[19,20,21,22,23,24,25,26,27,28,29,30]. Highly conductive n-type and transparent ZnO films were readily obtained by doping with B, Al, Ga, In, and F. Al is the most commonly studied dopant in ZnO films in all growth techniques. Igasaki et al.[4] reported growth of ZnO:Al with a resistivity as low as 1.4x10-4 Ωcm from r.f. sputtering. Sato et al.[8] reported a resistivity of 6x10-4 Ωcm from d.c. sputtering. Using chemical beam deposition technique, the same group reported a resistivity of 3.4x10-4 Ωcm[31]. Tang & Cameron[32] obtained a resistivity of 7x10-4 Ωcm from a sol-gel process. Hu and Gordon[33] achieved a resistivity of 3.0x10-4 Ωcm from MOCVD process. Structured Materials Industries, Inc. (SMI) ha