An etching and electrolyte solution called "UNIEL" has been found to be useful for electrochemical characterization as a function of depth ("electrochemical profiling" for short) of semiconductor compounds of elements from periods III and V of the periodic table; that is, InP- and GaAs-based semiconductors. UNIEL is a mixture of three solutions denoted A, B, and C in the volume proportions of 1, 4, and 1, respectively. The compositions of these solutions are the following:
- Solution A: 5 parts by volume of a 48-percent aqueous solution of hydrofluoric acid + 1 part by volume of a 99-percent aqueous solution of acetic acid + 2 parts by volume of an 85-percent solution of ortho-phosphoric acid + 100 parts by volume of water;
- Solution B: 0.1 molar N-n-butylpyridinium chloride; and
- Solution C: 1 molar NH3F2.
Electrochemical profiling can contribute to characterization and thus to the development of layered InP- and GaAs-based semiconductor device structures for photovoltaic cells. Current-vs.-voltage, capacitance-vs.-voltage, and conductance-vs.-voltage characteristics obtained by electrochemical profiling can be used to determine surface and bulk semiconductor properties like diffusion length, lifetime of minority charge carriers, surface recombination velocity, and concentration of majority charge carriers at any depth (see figure).
Prior to the development of UNIEL, six other solutions had been used for chemical profiling solutions of III -V semiconductors. None of the previously developed solutions had been found to be useful on all III -V semiconductor compounds, and neither has UNIEL. However, of all the solutions, UNIEL appears to be useful on the greatest variety of III -V compounds. In particular, it has yielded very good results in tests on n- and p-doped InP and GaAs substrates and homo- and heterostructures made of InP, GaAs, InGaAs, and InGaAsP layers. Preliminary studies have also shown that similar electrolytes based on UNIEL work fairly well for profiling GaP, AlGaP (with high Al content) and InGaSbP epitaxial layers, even with Si and Ge substrates.
This work was done by Maria Faur, Dennis J. Flood, Philip P. Jenkins, and David M. Wilt of Lewis Research Center and Mircea Faur and Manju Goradia of Cleveland State University. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.comunder the Materials category, or circle no. 105 on the TSP Order Card in this issue to receive a copy by mail ($5 charge).
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