VSTEP-BASED SMART PIXELS

With focus primarily on the laser-mode VSTEP (vertical-to-surface transmission electro-photonic device) with high-intensity light ouput and narrow optical beam divergence, the design features such as threshold gain and optical absorptivity, device fabrication, and characteristics such as optical switching are reported. A 20 mum 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(T), a double mesa structure VSTEP is fabricated. The whole mesa is covered with Au to utilize the threshold reduction by photon recycling. As a result, eta(T) has been improved to 11% at 1 mW light output. Then, two approaches to achieving VSTEP-based smart pixels are presented.