AIGaAs/GaAs Heterojunction Charge-Coupled Devices (CCDs) For Visible/Near Infrared Imaging Applications

The use of AlGaAs/GaAs Schottky gate, heterojunction CCDs for visible/NIR imagers offers a number of distinct advantages over the use of silicon MOS homojunction CCDs, several of which are of particular importance for space applications. The use of the heteroepitaxial technology possible with the GaAs/AlAs alloy system allows the design of devices each of whose layers is optimized to a specific functions. A CCD imager, for example, has a wide bandgap electrically inactive AlGaAs layer for optical access to the device, a narrow bandgap p-GaAs layer as an optical absorber for good response to the visible-NIR spectrum, end an intermediate bandgap n-AlGaAs CCD channel for charge transfer and low dark current. adapting glass bonding technology originally developed for III-V photocathodes, a backside illuminated CCD can be realized which eliminates optical obscuration from the CCD gates. Finally, the fundamental properties of the AlGaAs/GaAs system together with the use of Schottky barrier gates eliminates cross-talk and blooming and results in a device which is intrinsically radiation hard. During this presentation, the above considerations will be discussed in detail and the status of the development program at Rockwell International will be summarized. Important demonstrations including glass bonded, backside illuminated imaging and the observation of room temperature dark currents <100 pA/cm2 will be descirbed.