High quality substrates are a critical requirement for the epitaxial growth of high performance Group III-V (GaSb, InP, GaAs) or II-VI (MCT) based IR detector structures. Techniques such as MBE, LPE or MOCVD used to grow complex multilayer structures where the bulk and surface characteristics of the underlying substrate strongly influences the quality of the deposited device layers and thus the performance of the detector fabricated too. And whilst for Group III-V substrates, ‘epitaxy ready’ surfaces are very much the norm with no surface pre-treatment required prior to growth, much debate exists over whether it is possible to prepare Cadmium Zinc Telluride (CZT) substrates in the same way with commercially available substrates often etched or pre-polished prior to epitaxial growth. In this work we discuss the key factors which determine the ‘epi-readiness’ of a compound semiconductor substrate and identify the challenges which are associated with polishing ternary materials when compared with binary compounds. We also discuss the role which bulk CZT crystal quality plays on chemo-mechanical polish surface quality and the importance of substrate selection and screening steps to ensure that high quality substrates are obtained. We also compare the maturity level of infrared substrate materials such as GaSb with CZT and propose how CZT substrates can be chemo-mechanically polished in a production setting with the same tool sets as used to produce volume quantities of III-V compound semiconductor substrates in epitaxy ready form, as opposed to smaller scale, bespoke finishing processes. A forward looking view is given on the potential to align II-VI and III-V substrate manufacturing technologies in a way that supports product standardization and conformity at a time when demands for IR specification substrates is forecast to increase. Not only in quantity but also size where more stringent bulk and surface quality is required if state of the art, very large format detectors are to be delivered.
Cadmium Zinc Telluride (Cd1-xZnxTe or CZT) is a ternary II-VI compound semiconductor material that has been widely used in infrared detector applications for many years. Due to its lattice spacing, CZT is the substrate of choice for stabilizing Mercury Cadmium Telluride (Hg1-xCdxTe or MCT) crystal layer growth where the lattice matching reduces stress during detector growth processes for high performance infrared detectors and focal plane (FPA) arrays used in guidance systems and a wide array of IR applications. The manufacturing of high performance MCT IR detectors requires CZT substrates of high quality for both bulk and surface conditions thus enabling high quality MCT epitaxial layer crystallinity and low defectivity. In this work, we report on results on bulk CZT material grown using the Travelling Heater Method (THM) that are suitable for infrared focal plane array (IRFPA) detector applications. This proven crystal growth process has been used to manufacture CZT substrates meeting industry requirements of IR transmission, tellurium precipitate size, dislocations and of larger single crystal area. We will present results on chemomechanical (CMP) polishing of CZT substrates of square, rectangular and state-of-the-art round geometries utilizing standard production tool sets that are identical to those used to produce epitaxy-ready surface finishes on related IR compound semiconductor materials such as GaSb and InSb. Surface quality will be assessed by various analytical and microscopy techniques to validate the suitability of this material for epitaxial growth.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.