Growth of Er Doped si Films by Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition
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GROWTH OF ER DOPED SI FILMS BY ELECTRON CYCLOTRON RESONANCE PLASMA ENHANCED CHEMICAL VAPOR DEPOSITION
JIM L. ROGERS*, WALTER J. VARHUE* and EDWARD ADAMS** *Dept. of Electrical Engineering, University of Vermont, Burlington, VT 05405 **IBM Corp., Essex Junction, VT. 05452.
ABSTRACT Thin Si films doped with Er have been grown at low temperature by plasma enhanced chemical vapor deposition. The Er gas source is a sublimed organo-metallic compound fed into the process chamber. High doping concentrations without precipitation are possible because of the low deposition temperatures. The process relies on the beneficial effects of low energy ion bombardment to reduce the growth temperature. The ions as well as reactive chemical species are produced by an electron cyclotron resonance (ECR) plasma stream source. A hydrogen plasma stream is used to perform an in-situ pre-deposition clean to remove oxide from the Si surface. Film crystallinity and impurity concentration are determined by Rutherford backscattering spectrometry. INTRODUCTION Silicon is an indirect band gap semiconductor material and therefore is a low efficiency light emitter. This fact limits Si's potential for applications in the optoelectronics area. However, Si is presently the most important semiconductor material for the fabrication of solid state devices. There is a highly developed technology in the design and fabrication of Si integrated circuits for both logic and memory. This is due in part to Si's ability to grow a good thermal oxide as well as its other superior physical properties. Other than its inability to act as an efficient light source, Si is well suited for optoelectronic applications. It is transparent to wavelengths greater than 1.1 g.m and can be used to fabricate long wavelength devices and short wavelength optical receivers. Attempts to overcome Si's shortcomings have included the heteroepitaxial growth of III-V direct gap materials such as GaAs1 and InP on Si substrates. Another approach is to add impurities to the Si lattice which are luminescent. There is considerable interest in the use of rare earth dopants such as Er, Yb, Tm, Pr, Nd and Ho. The Er doped material is of particular interest because its luminescence peak is energetically located near the low loss, low dispersion window for optical fibers at 1.55 him. The origin of the emission is the internal transition within the 4f states of the Er+ 3 ion. The degenerate 4f electronic states of the ion must be split in the field created by the host lattice to permit the optical transition. Ennen et al. 2 have proposed the use of Si:Er for the fabrication of LED's and laser diodes. Attempts have been made to build Si:Er LED's using forward biased pn junctions as the pumping source. 3 A sharply structured electroluminescence spectrum at 1.54 girm was observed but the quantum efficiency was too low for device applications. An evaluation of Si:Er material for the fabrication of LED's and other devices was performed by Xie et. al.4 . It was concluded that Si:Er is not suitable for LED
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