  The Cadmium Zinc Telluride Imager (CZTI) onboard AstroSat is designed for
hard X-ray imaging and spectroscopy in the energy range of 20 - 100 keV. The
CZT detectors are of 5 mm thickness and hence have good efficiency for Compton
interactions beyond 100 keV. The polarisation analysis using CZTI relies on
such Compton events and have been verified experimentally. The same Compton
events can also be used to extend the spectroscopy up to 380 keV. Further, it
has been observed that about 20% pixels of the CZTI detector plane have low
gain, and they are excluded from the primary spectroscopy. If these pixels are
included, then the spectroscopic capability of CZTI can be extended up to 500
keV and further up to 700 keV with a better gain calibration in the future.
Here we explore the possibility of using the Compton events as well as the low
gain pixels to extend the spectroscopic energy range of CZTI for ON-axis bright
X-ray sources. We demonstrate this technique using Crab observations and
explore its sensitivity.
