Investigation of Anomalous n-Type Behavior in LWIR MBE-Grown Hg(1-x) Cd(x)Te Using Secondary Ion Mass Spectrometry (SIMS)

摘要

Residual impurities and process-introduced electrically active impurities have long been a source of producibility- and performance-related limitations in Hg(1-x)Cd(x)Te materials and devices. Considerable effort has been expended to reduce the impurity content of II-VI substrate materials and to control the level of both donor and acceptor impurities in thin-film sensing layers. In an effort to develop the next major breakthrough in Hg(1-x)Cd(x)Te materials and device technology, the Communications-Electronics Command (CECOM) Night Vision and Electronic Sensors Directorate (NVESD) has been working on a novel technology tool called the NVESD 'microfactory'. This MBE-based (molecular beam epitaxy) materials growth and device-fabrication tool is designed to allow for epitaxial materials growth, device fabrication, and passivation processes to be completed in situ in the vacuum system. However, controlled intentional doping of these layers has been hampered by high n-type background carrier concentrations in some of the layers after the mercury vacancy anneal. In this work we analyzed a number of MBE Hg(1-x)Cd(x)Te layers, bulk Cd(1-y)Zn(y)Te, and CdTe substrates using secondary ion mass spectrometry (SIMS) to qualitatively determine the major species responsible for the high n-type behavior and their possible sources.