IMPURITY SURVEY ANALYSIS OF CDXHG1-XTE BY LASER SCAN MASS-SPECTROMETRY

A laser scan mass spectrometry (LSMS) technique has been applied to th e analysis of epitaxial layers and bulk CdxHg1-xTe (CMT) materials. Th e samples are raster scanned under a focused Q-switched Nd-YAG laser b eam which ionises all elements with approximately unit sensitivity. Th e ions are extracted into a high-resolution mass spectrometer and inte rpretation of the mass spectra gives a complete impurity survey of the material with detection limits down to 1 part in 10(9) (3 x 10(13) cm (-1)) in bulk materials and 5 parts in 10(9) in epitaxial layers. Surf ace impurities are effectively removed in the first scan and subsequen t scans over the same area give a true measurement of the impurities p resent in the material. Successive erosion of the sample surface gives impurity depth profiles with the thickness of material eroded in each scan variable between 1 and 4 mu m. Results are given for impurities found in bulk CMT grown by standard Bridgman and ACRT (accelerated cru cible rotation technique) processes and in epitaxial CMT produced by l iquid phase epitaxy (LPE), metal organic vapour phase epitaxy (MOVPE) and molecular beam epitaxy (MBE). Bulk material is shown to be purer i n general than epitaxial material. Semiquantitative depth profiles of dopants in CMT, such as iodine, arsenic and phosphorus, can also be ob tained and comparative LSMS and secondary ion mass spectrometry (SIMS) depth profiles showing good agreement are given for arsenic in an MOV PE layer.