Photoassisted MBE of II-VI Semiconductor Films and Superlattices
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PHOTOASSISTED
MEE OF I1-VI SEMICONDUCTOR AND SUPERLATTICES
FILMS
N.C. GILES*, R.L. HARPER**, J.W. HAN, AND J.F. SCHETZINA Dept. of Physics, North Carolina State University, Raleigh, NC 27695-8202 *Present Address: Dept. of Physics, West Virginia University, Morgantown, WV 26506 "**Present Address: Dept. of Physics and Astronomy, Western Kentucky University, Bowling Green, KY 42101 ABSTRACT This paper will review recent progress in the growth of II-VI semiconductors at NCSU by photoassisted molecular beam epitaxy, an energy-assisted growth technique in which the substrate is illuminated during the entire growth process. The materials focused on here include undoped and As-doped CdTe, As-doped HgCdTe, and In-doped HgCdTe. These materials were grown as single epilayers, as well as incorporated in other structures including heterojunctions and modulation-doped superlattices. The photoassist during growth has allowed a substantial reduction in substrate growth temperatures, as well as an enhanced activation of n-type and p-type dopant species. The structural, electrical, and optical properties of the samples will be discussed below. INTRODUCTION The family of II-VI semiconductors has long received interest from the electro-optics community owing to their wide range of bandgaps from the ultraviolet (UV) to the infrared (IR). Efforts in recent years at laboratories around the world have focused on the lingering problem of establishing control over n-type and ptype doping in the II-VI's. In 1986, at North Carolina State University (NCSU), a new growth technique called photoassisted molecular beam epitaxy (MBE) was reported to give control over ntype and p-type doping in CdTe (1,2]. The first all thin film insitu-grown CdTe pn-junction was reported soon after the initial work (3]. Enhanced doping using the photoassisted technique has since been reported in other II-VI semiconductors, including thin films of CdMnTe and CdMnTe-CdTe superlattices (4], and HgCdTe (5]. Reports of devices made from these doped thin films [6-8] show great promise for future applications of II-VI materials. The intent of this paper is to summarize progress achieved at NCSU using the photoassisted MBE technique. An overview of experimental techniques and materials' properties will be presented. However, for a more detailed explanation of the many growth experiments pursued since 1986, the reader is advised to refer to the publications list in the reference section of the paper, and to companion papers included in this volume. The materials systems that are focused on here include undoped and doped CdTe and HgCdTe. The dopant species which have been employed are As as a p-type dopant, and In as an n-type dopant. The parameters used in the various growth experiments are summarized in the following section. A description of the structural, electrical, and optical properties of selected films and multilayer structures then follows. Mat. Res. Soc. Symp. Proc. Vol. 161. @1990 Materials Research Society
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EXPERIMENTAL
DETAILS
The CdTe and CdTe:As
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