Electron beam induced current assessment of doped and diffused junctions in epitaxial Cd xHg 1−xTe

Abstract

Electron beam induced current (EBIC) measurements have been applied to shallow-angle bevelled sections through Cd x Hg 1- x Te (CMT) epitaxial layers containing p-n junctions. Samples studied include (a) fully doped homo- and heterostructures grown by metalorganic vapour phase epitaxy (MOVPE) and (b) vacancy-doped CMT layers grown by MOVPE or liquid-phase epitaxy (LPE) where the junction has been formed by ion-beam milling or Hg in-diffusion from a surface oxide layer. The bevelled sections were formed by chemical etching and profiles of the bevel surfaces were measured to enable accurate junction positions to be obtained. For grown junctions, chemical dopant profiles determined by secondary-ion mass spectrometry (SIMS) and the position of the electrical junction, from Hall and strip depth profiling, agree with the position of the electrical junction revealed by EBIC studies. For junctions formed in MOVPE samples by Hg in-diffusion from a surface oxide, EBIC reveals contrast consistent with interspersed p and n regions. These observations can be explained by uneven Hg diffusion including fast diffusion down defects producing n-type channels within a p-type matrix. This effect was not observed in MOVPE samples with doped or ion beam milled junctions or LPE samples with diffused junctions, highlighting the difference between the microstructure of MOVPE and LPE CMT. EBIC assessment can provide an indication of the likely performance of test devices.