  The Soft Gamma-ray Detector (SGD) on board the NeXT (Japanese future high
energy astrophysics mission) is a Compton telescope with narrow field of view
(FOV), which utilizes Compton kinematics to enhance its background rejection
capabilities. It is realized as a hybrid semiconductor gamma-ray detector which
consists of silicon and CdTe (cadmium telluride) detectors. It can detect
photons in a wide energy band (0.05-1 MeV) at a background level of 5 x 10^-7
counts/cm^2/s; the silicon layers are required to improve the performance at a
lower energy band (<0.3 MeV). Excellent energy resolution is the key feature of
the SGD, allowing it to achieve both high angular resolution and good
background rejection capability. An additional capability of the SGD, its
ability to measure gamma-ray polarization, opens up a new window to study
properties of astronomical objects. We will present the development of key
technologies to realize the SGD: high quality CdTe, low noise front-end ASIC
and bump bonding technology. Energy resolutions of 1.7 keV (FWHM) for CdTe
pixel detectors and 1.1 keV for Si strip detectors have been measured. We also
present the validation of Monte Carlo simulation used to evaluate the
performance of the SGD.
