Interface abruptness in LPE grown (CdHg) Te layers on CdTe substrates

Abstract

The abruptness of interfaces between liquid phase epitaxial grown layers of Cd x Hg 1 - x Te and the CdTe(111) substrates on which they are grown has been studied by four techniques used for compositional profiling. These are: (i) energy-dispersive electron probe micro-analysis (ED-EPMA) at 5 and 25 kV; (ii) wavelenght-dispersive electron probe micro-analysis (WD-EPMA) at 15 kV; (iii) secondary-ion mass spectrometry SIMS) using a 12.5 kV O + 2 primary beam and (iv) backscattered electron analysis analysis (BSE) in the scanning electron microscope at 15 and 35 kV. These techniques have been applied to specimens from a single epitaxial layer. The distances as for the 10% to 90% compositional transition were measured, and values varying from 2 mum for ED-EPMA to 0.23 mum for BSE analysis were found. These results indicate the misleading measurements of interface abruptness that can be obtained on epitaxial specimens if consideration is not paid to the spatial resolution of the measurement technique and the topographic structure of the specimen. The potential of the BSE technique for high resolution compositional profiling and two-dimensional mapping will be discussed and the causes of the erroneous results obtained with the other techniques will be highlighted. The fact that the interface abruptness in this LPE specimen (≤ 0.23 mum) is a factor of ten less than conventionally measured for LPE (CdHg)Te layers has important consequences for the use of LPE for the growth of multilayer IR detector structures.