Real-Time Monitoring and Control of HgCdTe MBE Using an Integrated Multi-Sensor System
Abstract
We present recent progress on the use of an integrated real-time sensing and control system for monitoring and controlling substrate temperature, layer composition, and effusion cell flux during MBE growth of HgCdTe epilayers for advanced IR detectors. Substrate temperature is measured and controlled in real-time using absorption-edge spectroscopy (ABES). This allows the substrate temperature to be maintained at +/-1.5 deg C from the desired setpoint, even during actuation of effusion cell shutters which under conventional thermocouple-based control would produce a substantial (10-15 deg C) temperature change. In situ spectroscopic ellipsometry (SE) is used for monitoring HgCdTe layer composition in real-time. We describe the development of a comprehensive temperature- and composition-dependent SE dielectric function database which can be used for accurate and precise monitoring of Hg(1-x)Cd(x)Te layer composition over a wide range of x-values, from 0.2 to 0.42. The composition changes inferred from the real-time SE measurements obtained during growth of a two-layer structure are in excellent agreement with actual composition vs. depth profiles obtained using post-growth SIMS analysis. Likewise, the accuracy and precision of SE measurements conducted over multiple growth runs are shown to be suitable for robust SE-based composition control. Changes in gas-phase concentration of Cd atoms produced by a CdTe effusion cell are detected using an atomic absorption method (optical-absorption flux monitoring OFM). The OFM method allows changes in HgCdTe layer composition to be correlated directly with variations in Cd flux. The in situ optical sensors are linked using a custom software framework to provide the foundation for integrated, real-time monitoring and control of HgCdTe MBE growth of high performance IR detector structures over a wide range of compositions, layer thickness and substrate temperature.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1998
- Accession Number
- ADA400110
Entities
People
- G. L. Olson
- J. A. Roth
- J. E. Jensen
- P. D. Brewer
- R. D. Rajavel
Organizations
- HRL Laboratories