Development of An On-Chip Semiconducting Readout For Subsurface Optical Data

ABSTRACTA preliminary device was investigated as a first step in making an on-chip electrical readout based on the semiconductor CdS for a novel 3-D optical data storage method. The optical data is stored in glass as subsurface nanometer size defects called voxels. These voxels display secondary harmonic generation (SHG) to 800 nm input light. The device begins with an indium tin oxide film on a glass substrate coated with a film of Al2O3. In this preliminary device the Al2O3 was patterned via optical lithography with a periodic array of 10 micron holes that were filled with electrodeposited CdS. X-ray diffraction, and energy dispersive X-ray analysis were used to characterize the CdS. The device operation depends on the ability of the CdS with a bandgap of 2.4 eV to detect the 3.1 eV SHG light from the voxels while remaining unresponsive to 1.6 eV input light. The electrodeposited CdS was found to absorb 400 nm light at least a factor of 10 times greater than 800 nm light. Light to dark photocurrent ratios of 15 to 63 were observed from the CdS pillars using a 150 W xenon broadband light source. A light to dark ratio of about one was found when a long pass optical filter allowed only wavelengths above 750 nm. Thus the 10 micron CdS pillars have detected 400 nm light while rejecting the 800 nm input light.