A buffer layer of zinc telluride or titanium dioxide is formed directly on a silicon substrate. The azo derivatives of the present invention are designed to absorb at the low-energy ultraviolet, visible, or near-infrared region of the electromagnetic spectrum. For example, R1, R2, R3, and R4 each is C1-12 alkyl; Z1, Z2, and Z3 each is a single bond or \u20142\u2014; and ring A is 1,4-cyclohexylene or 1,4-phenylene. The doped areas of the coupled first and second main electrodes comprise an overlap to reduce cross-talk and to reduce silicon area. Each unique combination of binary data corresponds to a unique identity of the microchip.