VSTEP-based smart pixels

The design features and characteristics of a laser-mode vertical-to-surface transmission electro-photonic (VSTEP) device with high-intensity light output and narrow optical beam divergence are discussed. It is shown that a 20- mu m square VSTEP with an optimized vertical cavity structure demonstrates a low optical switching energy of 2.2 pJ, together with a low threshold current. In order to lower the series resistance, and to improve electrical-to-optical conversion efficiency eta /sub T/, a double mesa structure VSTEP was fabricated. The whole mesa is covered with Au to utilize the threshold reduction by photon recycling. As a result, eta /sub T/ is improved to 11% at 1 mW light output. Two approaches to achieving VSTEP-based smart pixels are presented.>