Algorithmic Multi-Color CMOS Avalanche Photodiodes for Smart-Lighting Applications

Future smart-lighting systems are expected to deliver adaptively color-tunable and high-quality lighting that is energy efficient while also offering integrated visible-light wireless communication services. To enable these systems at a commercial level, inexpensive and fast sensors with spectral-sensing capability are required. CMOS-compatible silicon avalanche photodiodes (APDs) can be an excellent fit to this problem due to their excellent sensitivity, high speeds and cost effectiveness; however, color sensing is a challenge without resorting to expensive spectral filters, as done in commercially. To address this challenge, we have recently designed and modeled a novel CMOS-compatible dual-junction APD. The device outputs two photocurrents simultaneously, one for each junction, and each junction is controlled independently via a bias voltage so that each photocurrent can exhibit its own avalanche amplification factors and sensitivity. What is unique here is that each APD responds differently to different wavelengths because of (1) the wavelength-dependent nature of the light-absorption profile in the device, and (2) the dependence of the avalanche multiplication process on the location of photon absorptions (and hence on wavelength). The idea is to produce a series of photocurrent pairs, at judiciously prescribed pairs of biases for each acquisition, which would contain sufficient spectral information about the light as well as its intensity, which can be extracted from the data via an algorithm. Modeling shows that we can ideally use a pair of biases to detect the color and intensity within 10 nm spectral resolution in the 440-650 nm wavelength range using a maximum likelihood (ML) algorithm. In practice, however, the spectrum and intensity must be calculated from the series of measured photocurrent pairs using a ML algorithm, which would employ the wavelength and bias-voltage dependent joint probability density function (pdf) of the two photocurrents. The pd