Characterization of InGaAsP materials by ultrahigh intensity post-ionization mass spectrometry: Relative sensitivity fac
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Characterization of InGaAsP materials by ultrahigh intensity post-ionization mass spectrometry: Relative sensitivity factors for zinc versus bulk constituents M. L. Wise, S. W. Downey, and A. B. Emerson AT&T Bell Laboratories, 600 Mountain Avenue, Murray Hill, New Jersey 07974-2070 (Received 14 June 1995; accepted 11 August 1995)
The first relative sensitivity factors (RSF) for detecting the major and dopant elements of optical materials by ultrahigh intensity post-ionization (UHIPI) mass spectrometry are determined. The post-ionization is performed using a single laser wavelength with intensities greater than 1014 Wycm2 . Zn-implanted InP and In0.4 Ga0.1 As0.3 P0.2 are used to investigate the photoionization of sputtered atoms and molecules. Under optimal conditions, the UHIPI RSF’s for atomic singly charged In, Ga, and Zn are nearly equal; that is, the ratio of UHIPI signals is equal to the concentration ratio. In principle, no standards are needed for quantitative analysis. Arsenic and P, with higher ionization potentials, are not detected as efficiently as other elements. The detected mass balance is usually group III rich. An entire mass spectrum is necessary for complete characterization of all elements and adjustment of their RSF’s because many sputtered molecules are detected containing the group V elements. Multiply charged species compose about 10% of the detected ions.
I. INTRODUCTION
We report here on a new characterization method for the elemental determination of dopant level and bulk constituents of optical materials. Ultrahigh intensity post-ionization (UHIPI) mass spectrometry combines many positive features of secondary ionization mass spectrometry (SIMS) and resonance ionization mass spectrometry (RIMS). Like both of these techniques, UHIPI uses ion beam sputtering to sample the material or structure in question, affording both depth profiling and surface analysis with excellent depth resolution. Because UHIPI is another form of sputtered neutral mass spectrometry (SNMS), using a laser to photoionize sputtered atoms and molecules (as is RIMS), it is relatively free from SIMS-type matrix effects.1 The main feature of UHIPI is that it can detect most elements with nearly equal efficiency. In principle, no standards are then needed for quantitative analysis. By contrast, SIMS requires a standard for each analyte determined in each matrix present in the sample. Remarkably, UHIPI detects all species similarly with one set of laser conditions. With RIMS, different laser wavelengths are required for each element to be determined because of the selectivity of the resonance process.2 In fact, RIMS is only quantum state selective and some atoms may not be detected if they are sputtered into nonground state electronic levels or bound molecules. UHIPI is therefore more like SIMS, where the ionization mechanisms is not element selective but J. Mater. Res., Vol. 11, No. 2, Feb 1996
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