The application of low dose SIMS to surface studies on compound semiconductors

Boyle, William John Ogilvie (1984) The application of low dose SIMS to surface studies on compound semiconductors. Doctoral thesis, City of London Polytechnic.


In this thesis secondary ion mass spectrometry is assessed as a surface analysis technique for compound semiconductor surfaces.

Two types of surface analysis problems are addressed - the use of SIMS to monitor cleaning of GaAs substrates in UHV for MBE growth and adsorption studies - and the use of SIMS in studying low coverage oxygen adsorption on MBE grown (111)PbTe and (100)GaAs surfaces.

As a monitoring technique for surface preparation, SIMS shows the presence of oxygen on (100)GaAs at coverages below the detection limit of AES. The detection of both intact and fragmented sulphate radicals conclusively demonstrates the sensitivity of SIMS to molecular cluster ions from contamination on the surface. This sensitivity proved a useful tool for determining the likely sources of contamination.

The sensitivity of the (111)PbTe surface to surface damage produced by ion bombardment, prevented a conclusive analysis of oxygen adsorption on this surface. Correlations are observed, however, between changes in the electrical conductivity of the PbTe which are Induced by ion bombardment and the SIMS signals from this surface. These correlations suggest that oxygen Interacts chiefly with Pb, as proposed by current models based on electrical assessment alone.

Differences are observed in the oxygen adsorption behaviour on (100)GaAs which are dependant on both the surface type, Ga-staballsed or As-rlch, and on the excitation state of the oxygen. The results are not fully conclusive because of difficulties in estimating surface coverages and in acquiring sufficient data using the configuration of the present SIMS apparatus.

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