Accumulation Mode Extrinsic Silicon

Since extrinsic silicon photoconductor material has high resistivity at cryogenic temperatures it can be used to form the substrate of an accumulation mode CCD as shown in Fig. 6.11. With an accumulation mode MIS structure the gates are biased so that majority carriers are stored and transferred down the insulator semiconductor interface. Local potential wells are formed under the gates however the dynamics of the charge transfer process will be very different from those for an inversion mode device since with an accumulation mode device the transverse electric fields will extend all the way to the back contact instead of being confined to the depletion region of an inversion mode structure. 

At low temperatures if the substrate has a thickness such that most of the IR radiation is absorbed we can estimate the resistivity by 

An electrode organization with the two well unit cell as shown in Fig. 6.13 allows horizontal and vertical scan registers external to the CID chip to read out the unit cells. Thus an m x CID array would require m -l- n connections to the IR sensitive material. Since the CID is xy addressed, random access to any 

Two well unit cell of a two-dimensional CID array demonstrating the readout and injection sequence. The electrode marked Vc. is attached to an x row line and the electrode marked Fqj, is attached to y column line. The column line will be attached to a preamplifier for readout. Note that the area under can be less than half the area of the unit cell 

SERIES PARALLEL SCAN InSb CID FOCAL PLANE ARRAY 

---

There exists a wide variety of approaches to the use of charge transfer devices in infrared focal planes. We shall discuss five high packing density, high quantum efficiency, approaches appropriate for series-parallel scan 1) IR sensitive CCD, 2) ctirect injection hybrid, 3) direct injection extrinsic silicon, 4) accumulation mode extrinsic silicon, and 5) infrared sensitive CID with silicon CCD signal processing. The reader is referred to a review article by Steckl et al. for a comprehensive discussion of a number of other approaches not discussed here which include indirect injection pyroelectric detectors and Schottky barrier photoemissive injection [6.1]. Three approaches in our list of five do not require... 

---