Effects of Boron Implantation on Silicon Dioxide Passivated HgCdTe
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EFFECTS OF BORON IMPLANTATION ON SILICON DIOXIDE PASSIVATED HgCdTe R. C. BOWMANI JR.*, J. MARKS*, R. G. DOWNING**, J. F. KNUDSEN 4ND G. A. TO The Aerospace Corporation, Laboratory Operations, P. 0. Box 92957 js Angeles, CA 90009 Center for Analytical Chemistry, National Bureau of Standards, Gaithersburg, MD20899 ABSTRACT The influence of boron ion implants on the optical and physical properties of photochemically deposited SiO2 films on Hg0 7 Cd0 3 Te and silicon has been investigated. The distributions of the boron atoms between the Si0 2 film and substrate have been determined by a nondestructive neutron depth profiling method. The implants produce an apparent densification of the Si0 2 films, which is accompanied by an increase in refractive index and changes in the infrared vibrational spectra for these films. INTRODUCTION Due to the inherent instability of the HgCdTe surface [1], various methods have been used to grow thin surface films that can passivate the material during the numerous processing steps required to fabricate infrared sensor devices [2]. It was recently shown [3] that photochemically (PC) deposited Si02 films can give greatly improved electrical properties for the photodiodes when compared to HgCdTe materials that were passivated with native or anodic oxides. However, the reproducibility of high quality PC-Si0 2 passivated photodiodes has not been very good and there are also problems with the adhesion of these films. Consequently, modifications to the original Hg sensitized deposition process [3] are being investigated [4] to produce improved PC - SiC2 films on HgCdTe. Ion implantation is commonly used [1,2,5-7] to form the diode junctions in HgCdTe photovoltaic devices. Implants through passivation films can produce significant differences in the electrical properties of the HgCdTe layer when compared to direct implants into uncoated samples. For example, an enhanced donor concentration was recently observed from Hall measurements [8] when boron ions were implanted through nominal 100 nm PC-Si0 2 films as compared to an identical implant into a Br 2 - methanol etched surface. This difference was correlated [8] with boron depth profiles that showed the boron concentration peak to lie immediately below the Si0 2-HgCdTe interface in the passivated sample; whereas, this maximum occured 100 nm deeper in the etched-only sample. Similar shifts in the boron profiles were also found from several other PC-Si0 2 passivated HgCdTe samples [8] for different boron implant energies. During these earlier studies, the ellipsometry data that had been obtained before and after the boron implants implied significant changes in the film thickness (d) and refractive index (n) were produced by the boron implants. This paper Certain commercial equipment, instruments, or materials are identified in this paper in order to adequately specify the experimental procedure. Such identification does not imply recommendation or endorsement by National Bureau of Standards, nor does it imply that the materials or equipment ide
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